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The ABC of demographic behaviour: How the
interplays of alleles, brains, and contexts over the life
course should shape research aimed at understanding
population processes
John Hobcraft
University of York
This paper proposes core innovations in the strategy of research on demographic behaviour. One aim is a
shift of attention away from events and towards a focus on dynamic processes and their interplay: away
from a preoccupation with marriage and divorce, births, deaths, migrations, and household structure
towards a broader perspective that takes account of partnership and intimacy, parenthood, potential and
well-being, position in society and space, and personal ties. Another aim is a much closer engagement with
genetics, neuroscience, psychology, and behavioural economics. A third aim is a strategy that pays more
attention to pathways within the individual, to the processes entailed when the individual interacts with
various contexts, and to progressions that involve the interplay of the pathways and processes through the
life course. These shifts of emphasis, which have already begun to occur, require a systematic reassessment
of priorities for research on demographic behaviour.
Keywords: demographic research; genetics; neuroscience; psychology; behavioural economics; theory;
research strategy; life course
[Submitted September 2004; Final version accepted January 2006]
Prologue
Demographic behaviour is at the core of human
existence, being concerned with the crucial and
intimate aspects of our lives. Research on the
determinants of demographic behaviour needs to
explore the roots of partnership, parenthood, well-
being, position in society and in space, and the
family as a key nexus of caring, intimacy, and
commitment. The ramifications of these essentials
of human existence in the way our lives play out are
reflected in the consequences of demographic beha-
viour. While these propositions are scarcely con-
tentious and are of profound individual and societal
importance, their import is often far from evident in
our research programmes.
This paper is concerned with how we investigate
demographic behaviour. One aim is to broaden the
research agenda in two key directions. The first of
these, covered in depth in Section 2, would entail a
shift towards a focus on dynamic processes and their
interplay, in place of a narrower focus on events. In
part this would require a change in emphasis from a
preoccupation with marriage and divorce, births,
deaths, migrations, and household structure to a
broader perspective that takes explicit account of
partnership and intimacy, parenthood, potential and
well-being, position in society and space, and perso-
nal ties.
The second broadening, covered briefly in Section
1.3 and in more detail in Sections 3.1 and 3.2,
envisages a much greater engagement with genetics,
neuroscience, psychology, and behavioural econom-
ics. Examples of the rapid progress that has been
made in these areas include the completion of the
Human Genome Project, the related extensive
emergent work on geneenvironment interactions,
and the advances in understanding of the key role
of neurotransmitters in human behaviour. These
developments challenge demographers to engage
with them and to enhance their understanding of
demographic behaviour by working in an interdisci-
plinary environment with geneticists and neuros-
cientists.
Population Studies, Vol. 60, No. 2, 2006, pp. 153187
ISSN 0032-4728 print/ISSN 1477-4747 online/06/020153-35 #2006 Population Investigation Committee
DOI: 10.1080/00324720600646410
A further aim is the deepening of the research
agenda that would be entailed in extending it to
encompass the following three domains: pathways
within the person, drawing on genetics (Section 3.1)
and neuroscience (Section 3.2); the processes in-
volved when a person interacts with others (Section
3.3) and with structures (Section 3.4); and the
progressions through the life course or over time,
involving the interplay of pathways and processes
(Section 3.5). The distinction between pathways
within the person and processes outside the person
is partly an expository convenience, since many of
the really interesting challenges and research agen-
das arise from the interplays, feedbacks, and inter-
actions among and within these domains.
These shifts of emphasis have wider implications
for how we approach the study of demographic
behaviour, some of which are sketched in the
remainder of Section 1: more targeted but highly
interdisciplinary prospective studies; a much sharper
focus on conceptualization, measurement, and mid-
level theories to help structure the pathways through
the complexity introduced by this broadening and
deepening; links to other disciplines, especially
genetics, neuroscience, and psychology; a shift
away from ‘monocausal’ approaches towards under-
standing pathways, processes, and progressions.
Many of these shifts of emphasis have already begun
to occur, but their ramifications require an explicit
reassessment of priorities for research on demo-
graphic behaviour. These are considered in a brief
conclusion that reviews some of the key issues raised
by this paper and outlines some of the wider
consequences.
The research agenda considered here is a daunting
one. Demographers are only beginning to engage
with behavioural genetics and have barely engaged
at all with neuroscience or behavioural economics.
Yet the importance of these areas for understanding
demographic behaviour makes it essential that we do
so engage. Within 10 years, it is likely that much
research on demographic behaviour will routinely
incorporate elements of molecular genetics and
neuroscience, and that we shall also have engaged
very explicitly with psychology as a discipline. This
may be a conservative prediction in view of the pace
of change: for example, very little serious new work
on dementia can ignore the APOE gene (Ewbank
2004) and whole journals are devoted to both
molecular and biological psychiatry.
Given the rapidity with which these topics have
emerged, it is impossible for one author to offer a
full prescription of how demography could or should
respond to them. However, it seemed worth making
an attempt to review some of the issues, methods,
and approaches and draw out at least some of the
ramifications for demographic research. This has
involved trying to get to grips with a broad and fast-
moving literature. I hope the results will at least
provide some foundations for further development.
Prospective studies
The complex interplay of phenomena that shapes
demographic behaviour means that our understand-
ing of it needs to be rooted in broad-ranging, large,
and thus expensive prospective studies. Increasingly
our research projects use large-scale, nationally
representative prospective studies to explore some
of the pathways involved in demographic behaviour.
Interesting contrasts can be drawn between the UK,
which has a unique series of nationally representa-
tive birth cohort studies, and the USA, where many
studies did not begin until their subjects were in
their late high-school years or early adulthood and
where childhood was treated as an undesirable
‘black box’. The development of such studies has
increasingly involved the major coordination of
interdisciplinary teams. The following are among
good examples of studies established fairly recently:
the UNECE Generations and Gender Programme, a
comparative study of the family involving extensive
inter-centre and interdisciplinary collaboration; the
English Longitudinal Study of Ageing, which built
upon US experiences with the Health and Retire-
ment Study; the UK Millennium Cohort Study, the
latest in the unique series of birth cohort studies,
which is being used in part to evaluate the Sure-Start
Programme*a social welfare programme that pro-
vides support for deprived families; the Netherlands
Kinship Panel Study, an innovative study of family
networks; the US Fragile Families and Child Well-
Being Study, which has a sharper focus on children
born into less stable partnerships; and the US
AddHealth Study, which has especially rich contex-
tual information.
However, we still have some way to go in
developing studies that are both closely focused on
explaining particular aspects of demographic beha-
viour and sufficiently broad and multidisciplinary in
their compass for the purpose (see Seltzer et al. 2005
for the first fruits of a major investment in designing
a family study for the USA). Such studies could
enable us to make progress in discovering what
really matters and to start disentangling the mediat-
ing routes and feedbacks in the pathways, processes,
154 John Hobcraft
and progressions involved. In doing so, we shall have
to pay much closer attention to genetics, neu-
roscience, and psychology in understanding the
within-person pathways, as well as radically improv-
ing our theory, conceptualization, measurement, and
subtlety in dealing with experiences in both inter-
personal and institutional contexts
Mid-level theory
In order to achieve this transformation, we need to
place much greater emphasis on building and devel-
oping mid-level theories (for useful and quite
different takes on theory in demography see McNi-
coll 1992; Massey et al. 1993; Burch 1996, 2003a,b;
Van de Kaa 1996; Lesthaeghe 1998). The need for
mid-level theories is also emphasized by Seltzer et
al. (2005) in a recent synthesis concerning new
models for explaining family change and variation
(which also pays attention to the need to integrate
biology into our theories of demographic beha-
viour). Mid-level theories avoid the grand theorizing
that Brass (1986, p. 33) was criticizing when he
lauded demography for being ‘specific, pedestrian
and modest*underrated qualities in social science’
and, by implication, saw much social science as
concerned with ‘the speculative, the diffuse, the ill-
defined and the pretentious’. Such grand theories
often purport to explain everything but sometimes
explain very little; their overarching reach makes the
linkage to behaviour all too often an act of faith.
Examples are the trinity of G’s: God, Genes, and
Globalization, all of which are sometimes invoked as
‘ultimate causes’ in this way. In contrast, mid-level
theories remain reasonably targeted to particular
problems; often the steps towards such theories are
better described as frameworks for analysis. Mid-
level theorizing of this kind has received some
attention under the rubric ‘social mechanisms’ (see
Hedstrom and Swedburg 1998) and is closely related
to the concept of ‘middle-range theory’ proposed by
Merton (1957).
Some of these concerns can be illustrated on a
modest scale through the work on understanding
parenthood, undertaken in part with Kathleen
Kiernan. We began by elaborating a mid-level
conceptual framework that addressed the range of
elements we needed to consider in trying to under-
stand the process of becoming a parent and applied
this in a broad sweep to the interpretation of fertility
trends and variations in Western Europe (Hobcraft
and Kiernan 1995). Subsequently the same frame-
work was used in a more detailed consideration of
fertility levels and trends for England and Wales
(Hobcraft 1996). A further step in the process was
an attempt to elaborate the design required for a
much more focused study of the transition to
parenthood (Hobcraft 2002), which has influenced
though not determined the design of the more
omnibus UNECE Generations and Gender Pro-
gramme. More recently, an attempt was made to
elaborate some of the requisite within-person path-
ways that need to be considered (Hobcraft 2003).
But this endeavour to construct a framework for
understanding entry into parenthood, influenced
and informed by the work of many others along
the way, is incomplete. Other sustained attempts to
achieve better conceptual frameworks for under-
standing parenthood include those of Van de Kaa
(1987, 1996, 2004), Lesthaeghe (1995, 1998), and
Seltzer et al. (2005). This kind of conceptualization
and framing of theories is equally required in other
areas of demographic behaviour.
Links to other disciplines
Demography has always been an interdisciplinary or
multidisciplinary enterprise (e.g., Stycos 1987) and
has drawn on a wide range of approaches and tools.
However, we can still learn a great deal from other
disciplines that rarely feature among our collabora-
tors or in our training. In looking to these other
disciplines, I shall emphasize four ways in which we
can derive real benefits from them. Firstly, other
disciplines point to new and instructive ways of
structuring questions and problems. Secondly, they
provide alternative theoretical approaches and tools
for analysis. Thirdly, they provide a basis for new
knowledge and findings. Fourthly, they act as a
source of collaborators and potential recruits for
demographic research.
The biggest shift of focus towards multidisciplin-
ary work on demographic behaviour has come in the
field of ageing and health research (Singer and Ryff
2001; Wise 2001; Johnson and Crow 2005; Waite
2005). Here, although demographers have distinctive
insights to offer and have played a significant part in
developing the new approaches, the work is also very
clearly linked to a wide-ranging research agenda
that draws on many disciplines (e.g., Singer and Ryff
2001; Ryff and Singer 2005; see also Wachter and
Finch 1997 on longevity). Examples of this new
approach are the massive multidisciplinary effort
that went into the US Health and Retirement Study
ABC of demographic behaviour 155
and the newer English Longitudinal Study of Age-
ing. Moreover, many existing ageing studies now
collect biomarkers, including DNA (Finch et al.
2000). This shift in emphasis is beginning to have
an impact on other areas, such as child development
(Shonkoff and Phillips 2000) and underlies the
recent ‘NIH Roadmap’ for future research priorities
in the USA (Zerhouni 2003). The beginnings of this
wider approach are also evident in relation to
research on the biodemography of fertility and
family formation (Wachter and Bulatao 2003; Selt-
zer et al. 2005).
Engagement with psychologists and with psycho-
logical research should be an explicit and high-
priority agenda for progress in population research.
Interplays with psychology have already proved both
challenging and productive for economics (Brocas
and Carrillo 2003, 2004; Camerer et al. 2004; Layard
2005). We, too, can gain important insights into
decision processes, choice, and judgement from
behavioural economics. Much of demography is
also bound up with interpersonal relationships and
here we can benefit enormously from interactions
with social psychology (e.g., Fiske 2004) and with
affective neuroscience (Panksepp 1998). This en-
gagement should prove both challenging and fruit-
ful: psychology will not solve all our problems, but
there is a huge potential for the enrichment of our
approaches.
Psychology is the one discipline that grapples
seriously with the range of issues involved in the
programme for population research set out in this
paper. It brings together, sometimes uneasily, beha-
vioural geneticists, cognitive scientists, and social
psychologists, and involves collaboration with ge-
neticists, neuroscientists, and social scientists. Its
crucial concerns include the genome, mind, brain,
emotions, decision-making, the person, relation-
ships, and social context. Some of the best work
explores interplays among these different elements.
Close attention is sometimes paid to the design of
studies, especially genetically informed designs,
along with rigorous discussions of the issues involved
(e.g., Rutter et al. 2001; Plomin et al. 2003a). A
major focus is on trying to elucidate pathways,
processes, and mediators. The widespread use of
structural equation models forces investigators to
seek conceptual clarity about interlinkages and
pathways that matter. There is sometimes a very
constructive concern with trade-offs between ‘thick’
and ‘thin’ measurement (the rich yield of small-scale
qualitative or observational studies and the humbler
but representative fare of large-scale surveys).
Demography and other social sciences could prob-
ably benefit from some of the more rigorous
techniques used in the small-scale studies, such as
the use of double-blind rating of qualitativeor
observational material.
On the other hand, there are many features of
demographic research that could usefully shape our
engagement with psychology. Paramount among
them is our interest in whole populations, rather
than small-scale unrepresentative samples or the
psychopathologies of individuals. We are already
engaged with the very different style of in-depth
studies used by anthropologists and can benefit from
the enrichment and cross-fertilization offered by
both approaches.
Much of the agenda laid out in this paper also
requires us to engage with the life sciences. We have
much to gain from genetics, neuroscience, endocri-
nology, and evolutionary theory, and from working
with relevant scholars to make progress on bringing
these areas into demographic research in a focused
and precise way. These issues are discussed in much
greater depth in Section 3.
Evolutionary thinking, especially as found in
evolutionary psychology and evolutionary ecology,
has much to reveal about survival, mating, and
reproduction, and it has begun to make some impact
on demography in recent years (e.g., Diamond 1997;
Gangestad and Simpson 2000; Low 2000; Clarke and
Low 2001; Gangestad 2003; Haaga 2003; Kaplan and
Lancaster 2003; Worthman 2003). Bringing together
evolutionary and economic (and other) theories
about mate choice or reproductive behaviour and
examining their (fairly common) basic assumptions,
for example about gender roles, could ultimately
prove quite fruitful (Hobcraft and Kiernan 1995;
Lam 2003). One of the great challenges, though, is to
formulate evolutionary theories in the form of
testable propositions and to sort out the useful
constructs from the enticing speculation (see Lick-
liter and Honeycott (with discussion) 2003; also
Freese and Powell 1999 and the comment by
Kanazawa and reply 2001, and De Waal 2002).
In a different vein, Freese et al. (2003) provide a
very useful review of how work on several of the
topics covered in this paper is of relevance to
sociology*including evolutionary psychology, be-
havioural genetics, and proximate biomarkers such
as testosterone and serotonin. They also predict the
probable emergence of an important role for neu-
roscience and fMRI (functional magnetic resonance
imaging of the brain) in particular. Again, this
material has some potentially useful insights for
demography.
156 John Hobcraft
Understanding, description, and causation
Key themes of this paper are the importance of
pathways rather than single causes, the probably
crucial role of interplays and interactions, and the
need to move away from ‘black-box’ approaches and
capture as much as possible through measurement.
Implicit in this approach is the need to discover
whether and how far relationships are contingent,
both on context and on individual experiences.
Much demographic (and other social) research
mainly explores relationships between demographic
phenomena and omnibus variables, such as educa-
tion, social class, or income. There is a need to
elucidate the pathways by which such variables are
linked to demographic behaviour, to identify the key
components that matter, and to explore the indivi-
dual attributes that mediate responses. This poses
difficult challenges, but arguably will improve our
ability to target policies and certainly will help
towards better understanding.
The use of the term ‘understanding’ throughout
this paper represents a very deliberate attempt to
identify a middle way between description and the
thorny issue of causation. Of course, such sharp
distinctions are not fully achievable since description
and causation overlap with understanding or expla-
nation (see, for example, Chapter 1 of Woodward
2003). The elaboration of progressions and of mid-
level theory is an intrinsic part of this approach and
relates to the burgeoning field of life-course research
(Mortimer and Shanahan 2003, particularly Chap-
ters 1, 6, 18, and 27), which has already had some
impact on demographic research (Shanahan 2000;
Hogan and Goldscheider 2003). An excellent ac-
count of many of the deeper issues involved in
gaining understanding from exploring longitudinal
data is provided by Rutter (1994).
A great deal of recent work in econometrics has
been focused on the challenging task of trying to
assess whether an observed association between
(often only) one antecedent and an outcome is
causal. This work is often ingenious and technically
sophisticated (e.g., a summary statement from one of
the major contributors*Heckman 2000; for differ-
ent takes on similar issues see Winship and Morgan
1999, and Little and Rubin 2000; for accessible
accounts of the issues aimed at demographers
see Moffitt 2003, 2005). However, causality cannot
be established through ever more technical tricks
in statistical models: ‘... there is no mechanical
algorithm for producing a set of ‘‘assumption free’’
facts or causal estimates based on those facts’
(Heckman 2000, p. 91). It is salutary to note that
there is increasing recognition of the fact that even
randomized controlled trials cannot reveal relation-
ships that are heavily contingent and involve path-
ways through time: ‘randomized trials can never
estimate channels for the effects of treatment’
(Moffitt 2003, p. 453). Rosenzweig and Wolpin
(2000) provide a deep discussion of some of the
related problems in assessing ‘natural experiments’
and O’Connor (2003b) gives an insightful psycholo-
gical slant on ‘natural experiments’. A clear distinc-
tion between self-selection and social causation has
also penetrated psychology, though, unlike much
econometric work on these issues, with an emphasis
on understanding pathways and on measurement
(Caspi 2004) rather than on modelling and unobser-
vables (which are all too often only unobserved).
These deep and unresolved issues of causality
have spurred much debate from a wide range of
disciplines (see Freedman 1991; McKim and Turner
1997; Cartwright 1999; Pearl 2000; Glymour 2001;
also Fricke 2003; Moffitt 2003; and Smith 2003 on
demographic research). Although such issues are of
profound importance we shall not attempt to cover
them in further detail here.
In a fascinating and thoughtful paper Lieberson
and Lynn (2002) advocate biology as providing a
more appropriate paradigm for sociology than
physics (mediated through economics). They suggest
that a more applicable approach to linking research
and theory would be to adopt several key elements
of Darwin’s approach to evolution. The key features
of the Darwinian programme that Lieberson and
Lynn (2002, p. 1) identify and endorse at some
length are: ‘... drawing rigorous conclusions based
on observational data rather than true experiments;
an ability to absorb enormous amounts of diverse
data into a relatively simple system that did not
include a large number of what we think of as
independent variables; the absence of prediction as a
standard for evaluating the adequacy of the theory;
and the ability to use a theory that is incomplete in
both the evidence that supports it and in its
development.’
The emphasis on a holistic approach or on a
system rather than on variables is related to, but
subtly different from, the recent emphasis among
many psychologists on ‘person-centred’ as opposed
to ‘variable’ approaches to analysis (e.g., Bergman et
al. 2000; Singer 2001). Lieberson and Lynn also
make important points about the nature of causal
chains, the role of time (which is relevant to the
‘stickiness’ of early fertility decline), and the im-
portance of engaging with other disciplines. All of
ABC of demographic behaviour 157
their discussion is also highly relevant to how we do
demographic research.
Of particular relevance is the distinction between
understanding (or explanation) and prediction. Even
if we succeed in obtaining a complete explanation
for past partnership or reproductivebehaviour, this
would not be likely to make possible the prediction
of what would happen to partnership or fertility
behaviour in the future since too many other
predictions would be required. However, we would
be better placed to answer contingent (or ‘what-if’)
questions and would probably be better able to
predict the effects of policy.
Processes not events
Why should we concentrate on processes and not
just events for research into understanding demo-
graphic behaviour? A narrow concentration on
events has certain analytic advantages, including
ease of measurement, convenience for analysis, and
clarity of focus. However, though valuable as a
descriptive tool, the life table or a set of fertility
rates (and their more sophisticated cousins such as
baseline hazards) make very little contribution to
understanding. The limitations of traditional ap-
proaches to describing group differentials are well
recognized. Demography needs to move further
towards dealing with the understanding of dynamic
processes. A key goal is to enrich and deepen our
understanding of the pathways involved in determin-
ing demographic behaviour and its consequences.
This goal requires greater attention to theoretical
frameworks and to processes. A second goal is to
broaden the terrain we consider, in acknowledge-
ment of the fact that such processes (e.g., becoming
a parent or maintaining health) require a wider
focus than has typically been used to date. Such
considerations can also usefully challenge existing
orthodoxies.
Although such events as marriage, birth, or death
are of importance in their own right and often have
clear symbolic meanings, it is imperative that we
recognize that they are not the only elements in
changes of state or status that matter for demo-
graphic behaviour, or that have widely differing
consequences. The implications of parenthood alter
with family size, age of the child, and in relation to a
whole host of other factors. The shift to cohabitation
or the fuzzier shifts in time allocation, degree of
autonomy, or level of attachment during a partner-
ship are all of consequence both for partnership
breakdown and for choices about entry into parent-
hood or for childrearing arrangements. Subtle shifts
in health and well-being status have important
implications for living arrangements, employment,
transfers of time and money, and many other aspects
of life. The process of deciding (or not) to change
place of residence (or job) is complex and involves
many steps (or events) along the way, but also
interplays with many other important processes,
both demographic and other. These other processes
range from environmental triggers for gene expres-
sion, or brain plasticity, through to shifts in institu-
tional or other contextual influences on the person.
Recognition of these complexities not only poses
formidable analytic challenges, but also makes it
much more necessary that we identify the factors
likely to be important in determining demographic
behaviour or its consequences. This requires greater
conceptual clarity. We need to spend more time
thinking through and sifting evidence on what may
be the important connections across a wide range of
disciplinary perspectives and to pay greater atten-
tion to issues of ‘causal ordering’ or mediating
routes through the many elements involved. This
requires clarification of what may be the proximate
real determinants, what may be the intermediate
prior antecedents, and so on backwards to possible
‘ultimate’ causes (see Bronfenbrenner 1986).
To give but one example in the realm of parent-
hood and its relationship to values, beliefs, attitudes,
and ideas, it seems highly plausible to propose that
those explicitly relating to parenthood are likely to
be the most directly influential; a step backwards
might look at channels through world views or
religiosity, and then there are more remote questions
as to how globalization (or genes or evolution or
neuroendocrine systems) might act through these
(and other) mediating routes. All elements in the
chain of influence could be the subjects of legitimate
research questions, but we have to make greater
efforts to track through the chain. Miller et al. (2004)
provide a valuable contribution to elaborating such
pathways in their traitsdesiresintentionsbeha-
viour framework for a couple’s fertility motivation
(see also Ajzen 2001). I believe that when headway
is led by demographers it will usually begin with the
proximal determinants and gradually trace routes
backwards (Hobcraft 2003).
But tracing the routes forwards is an equally
important enterprise, perhaps led by those in other
disciplines (e.g., behavioural geneticists), but where
demographers should have important and influential
inputs. Even where we do not exert this influence,
we nevertheless need to monitor and absorb results
from elsewhere and be equipped to criticize and
158 John Hobcraft
inform those who over-interpret their findings. It is
interesting that a psychiatrist and a demographer
quite independently chose differing propensities for
risk-taking behaviour as an illustrative example of
potentially important genebrainbehaviour path-
ways for aspects of human reproductive behaviour
(Hobcraft 2003; Rutter 2003a). Both emphasized the
multiple and reinforcing effects that could arise for
reproduction through the life course, for example, in
adolescent sexual activity, inadequate contraception,
infidelity, and divorce.
Moreover, improvements in knowledge, measure-
ment, and understanding have increasingly made
clear that most ‘events’ are relatively fuzzy and very
often part of more prolonged processes. One illus-
trative example is the study of leaving the parental
home, which began to receive serious attention
during the 1980s (Grebenik et al. 1989). It is clear
that, for many families, the departure of children is a
protracted process with complex and repeated
departures and returns.
Partnership and intimacy not just marriages and
divorces
Demographers working on developed societies have
been forced to abandon their focus on formal
marriage because of the rapid changes in partnership
behaviour that have occurred over the past few
decades. Our roots in civil or parish registration
and simplistic questions in censuses and surveys
inhibited understanding. Those working on less
developed countries that lacked registration systems
had long been more aware of consensual unions and
those working in the Caribbean in particular had
been aware of long-term visiting unions. Developed-
country demographers have relabelled consensual
unions as cohabitation and visiting unions as ‘living
apart together’ (LAT) or ‘romantically involved’
relationships. The meaning and nature of marriage
has altered quite radically in much of the world.
Entry into a partnership has always been a
process, with many steps along the way. The locus
of control in the process has often shifted away from
parents, other relatives, and community leaders to
the individuals concerned, but the identification and
sifting of potentially suitable partners is an intrinsic
part of what goes on, even where the couple first
meet at the time of the marriage (as happens
frequently in upper rural Egypt, for example *see
Hussein 2002). There are almost always clearly
identifiable transitions along the way, although the
sequencing of attachment, sexual intercourse, living
together, and any formal betrothal or marriage can
vary significantly, with the latter elements some-
times being optional. Yet these sequences surely
have major implications for the nature of the
relationship. Contrast an arranged marriage in a
patrilocal society, when the partners first meet at the
marriage and the bride moves to a distant village
away from her friends and family, with one where
the couple form an ongoing attachment and become
sexually intimate before cohabiting and eventually
deciding to marry. Marriage in these two contexts
does not even have the same symbolic meaning, let
alone constituting the same key precursor of in-
timacy and reproduction. The partnership context of
parenthood in this sequence can also vary signifi-
cantly and the desire to become a parent may play
an important part in decisions to cohabit or marry.
Societal and gender structures clearly deeply affect
the nature of these processes and also partly
determine the consequences of marriage for the
individuals concerned.
Decisions about reproduction also have roots in
the nature of the relationship, which evolves over
time. The shy young bride, for example, in parts of
the Indian sub-continent or rural Egypt, who first
meets her husband at the wedding and then moves in
with his family or into his village gradually adapts
and adopts new behaviour. A generation later she
will have become the mother-in-law who may con-
trol the destiny of her son’s new bride. In between a
wide variety of experiences, which may range from
domestic violence to attachment and intimacy,
emerging autonomy, and success in childbearing
and childrearing may all have played a part in
changing the nature and meaning of the relationship,
as will employment, land tenure, and a range of
external forces. Although much of the negotiation
process may take place before cohabitation or
marriage, a similar evolution in the nature of
intimate relationships takes places for the modern
Western couple.
Emotions play an important part in any long-term
relationship. A ‘good’ partnership can successfully
meet many of our basic needs for sex, for nurture,
and for intimacy (Panksepp 1998). On the other
hand intimate partnerships are sometimes also
associated with basic emotions of fear, disgust, or
anger (Fiske 2004). Demographers need to engage
with neuroscience and gain a better understanding
of the role of emotions in relationships (see also
Massey 2002). Moreover, we need to pay attention
to suggestions that pair bonding and love generate
lasting changes in brain structure (Young 2003). In
ABC of demographic behaviour 159
other words, the key importance of feedback loops
in relationship formation and breakdown need to be
included in our considerations. These issues are
discussed at greater length in Section 3.2.
Clearly partnership breakdown is a process too,
partially recognized by the distinction often made
between separation and divorce. The gradual dete-
rioration of a relationship can encompass many
elements, including sudden shocks such as the
discovery of infidelity, but breakdown also often
has lasting effects on all the individuals concerned,
differentially affecting the emotional, physical, and
socio-economic well-being of both partners and of
children. The opportunities and constraints of part-
nership breakdown also need to be incorporated
into our understanding. How far do the options for
dealing with a deteriorating relationship include all
of ‘exit, voice, and loyalty’? (see Rusbult et al. 1991
for an adaptation of Hirschman’s 1970 classic frame-
work in the context of relationships). What is the
relative importance of these options and their
consequences for the man and, usually more sig-
nificantly, the woman?
Since the pioneering work of McLanahan and
Bumpass (1988) and Kiernan (1992) on the con-
sequences of divorce for children, using nationally
representative samples, the recognition of the pre-
disruption stresses for children of a decaying part-
nership has been evidence of attention to process
(Cherlin et al. 1991). But partnerships break down in
avariety of ways, ranging from acrimonious and
possibly violent disputes following which the part-
ners hate each other, want no contact, and use child
custody as a weapon, to those in which the decision
to part is harmonious, and in which the partners
remain friends, have frequent contact with each
other, and share childrearing. The implications of
the partnership breakdown for all those involved,
perhaps most importantly for childrearing, are a key
concern.
One of the core features of partnerships that
demographers and others have rarely addressed
properly is their dyadic nature. Two key actors are
involved and both bring legacies of their inheritance,
upbringing, and past circumstances and behaviour to
the relationship. Yet all too often it is only the
characteristics of one partner that are examined
(examples of exceptions are Johnson and Booth
1998; Felmlee 2001). Moreover, both for dyads and
for the individuals involved, little attention has been
paid in large-scale studies to moderately stable
characteristics, such as personality traits (but see
Robins et al. 2000 and the useful review by Karney
and Bradbury 1995). A framework covering the
diversity of genetic, evolutionary, neural, and psy-
chological pathways and processes involved in part-
nership formation is given by Miller and Rodgers
2001; also see Spotts et al. 2004.
Parenthood not just births
It is curious how demographers have lost sight of
reproductivity, one of the key themes of work in the
subject up to the 1950s (e.g., Hajnal 1950). The
concentration on births as the key events is domi-
nant. Yet it is surely the case that few individuals or
couples choose to have a baby per se, although some
interpreters would see having a birth as fulfilling a
basic need to nurture (e.g., Foster 2000; Morgan and
King 2001; Hobcraft 2003). Rather, they have the
goal of producing socialized, healthy, and successful
or fulfilled adults, and perhaps also of satisfying
lineage obligations. For parents, even the traditional
demographic notion of reproductivity, which merely
requires survival, is inadequate. Possible motivations
for reproduction are also partially captured in the
evolutionary notion of fitness, which is concerned
with successful reproduction of the genes. The
concern with parental investments in a broad sense
also features strongly in discussions of behavioural
ecologists and evolutionary psychologists (e.g., Ka-
plan and Lancaster 2003; Worthman 2003). In
economics some of these concerns are encapsulated
in the notion of quality quantity trade-offs (Becker
1991; for a recent review linked to evolutionary
biology, see Lam 2003).
But, as argued at greater length elsewhere (Hob-
craft and Kiernan 1995; Hobcraft 2002, 2003), this
notion of becoming a parent and the long-term
nature of the investment should deeply affect the
way we view and analyse decisions about child-
bearing. In particular, over and above responses to
current circumstances, those who make choices
about becoming a parent need to make judgements
about prospects for the next 20 years or so, both at
the individual and societal level, and changes in
these mid-term security prospects have played a
significant part in fertility trends in the developed
world (Hobcraft and Kiernan 1995; Hobcraft 1996).
The mid-term security factors identified include
shifts in partnership stability, in welfare smoothing
over the life course, in child services, in income and
employment security, in housing circumstances, in
worklife balance, moneytime trade-offs, and
gender relations. The contribution of changes in
security (e.g., in employment, housing, and welfare
160 John Hobcraft
provision) to an understanding of the recent collapse
in fertility in Central and Eastern Europe is fairly
evident, although the relative balance between
short-term and mid-term elements is still unclear.
Moreover, there is a need for demography to
come to terms with the issues involved in rearing and
nurturing ‘successful’ citizens as part of our realm of
study. At the very least, these are among the key
consequences of the narrow demographic behaviour
of the event of a birth. As such, they form a
legitimate and important focus for our attention,
though we too often neglect the consequences of
demographic behaviour at the micro-level (these
issues have received some significant attention, for
example, Preston 1984; McLanahan 2004). Recogni-
tion of the potential importance of the fluidity of
partnership contexts early in the life of the child has
recently become a focus of attention both in the
USA and in the UK (Sigle-Rushton and McLanahan
2002; Kiernan and Smith 2003).
The process of becoming and of being a parent is
also bound up with a series of legacies of the past for
both parents and is subject to the constraints of
reproductive biology, personality and emotions,
genes, the means of control over reproduction, ideas,
and interpersonal and institutional contexts. More-
over, some cultures and groups (and indeed govern-
ments) still have strong pronatalist stances and there
is unresolved discussion about whether pronatalism
is intrinsic to the individual (Hobcraft and Kiernan
1995; Foster 2000; Morgan and King 2001). More-
over, as will be discussed in Section 3.2, individuals
differ in their weighting of immediate against future
consequences of their actions and in the extent to
which they believe they have anything to lose from
immediate childbearing, as well as in their responses
to accidental or unwanted pregnancies (e.g., Edin
and Kefalas 2005).
Potential or well-being not just death
We are all familiar with the WHO definition of
health as being a state of complete physical, mental,
and social well-being and not just the avoidance of
disease or death. Yet much demographic analysis,
using our staple tools of life tables and survival
analysis, is concerned just with death as an event.
However, owing in part to the influence of the US
National Institute for Aging, demographic research
on ageing has moved a considerable way towards
adopting a broader focus (e.g., Wise 2001 and
several earlier volumes; and the summary volume,
Waite 2005), though there is still an emphasis on
disease and morbidity rather than on positive health
(but see Singer and Ryff 2001).
The broad health agenda, involving the need to
increase cooperation across disciplines ranging from
molecular genetics through neuroscience, psychol-
ogy, public health, and medicine to the social
sciences is well encapsulated in Singer and Ryff
(2001). The same integrative theme is further devel-
oped later in this paper. However, in an influential
earlier paper, Ryff and Singer (1998) put forward a
persuasive case that resonates with this section (my
italics): ‘Positive human health is best construed as a
multidimensional dynamic process rather than a
discrete end state. That is, human well-being is
ultimately an issue of engagement in living, invol-
ving expression of a broad range of human potenti-
alities: intellectual, social, emotional, and physical’
(p. 2).
We need to learn from and engage in such
research. In particular, demographers have hardly
linked into nor learnt from research on hedonism
and eudaimonism (see Ryan and Deci 2001 for an
excellent and wide-ranging review). Briefly, hedon-
ism is concerned with happiness or subjective well-
being (see Diener et al. 1999), whilst eudaimonism is
concerned with the broader fulfilment of potential,
though there is a danger that cultural relativism
affects definitions of the latter (for example, a
tendency to overemphasize intellectual pursuits).
Well-being and mental health are implicated among
the pathways to physical health (Singer and Ryff
2001); see also the remarkable study of nuns linking
positive emotions early in life to subsequent long-
evity (Danner et al. 2001).
Happiness or subjective well-being has become a
serious research issue for economists recently, partly
in the hope that it might be indicative of utility,
and economists have been especially concerned to
note that subjective well-being and income are not
well correlated, especially among richer societies
(Kahneman et al. 1999; Frey and Stutzer 2002;
Layard 2005). There is some research to show that
subjective well-being is strongly related to, and
probably a consequence of, demographic behaviour:
experience of divorce matters as much as unemploy-
ment for short to mid-term unhappiness (Lucas et al.
2003; Kohler et al. 2005). However, there is also
much evidence that subjective well-being is signifi-
cantly linked to personality traits and that indivi-
duals adapt to changed circumstances within a few
months or years; extreme examples of this adapta-
tion have been shown both for lottery winners and
for paraplegics (Brickman et al. 1978; Frederick and
ABC of demographic behaviour 161
Loewenstein 1999; Ryan and Deci 2001; Layard
2005).
In a broader context, these concerns with positive
health link to a wide range of recent agendas,
including a human development approach (UNDP
annual), poverty alleviation and health (World Bank
2000), social exclusion as a concept in Europe and
elsewhere, and an approach to development that
emphasizes capabilities and functioning (Sen 1993,
1999). Ultimately living is about life not death. In
these approaches, the concerns are usually with
trying to ensure good functioning and development
of the capabilities required, rather than with the
culturally relative extremes of assessing eudaimonic
well-being.
Position not just migrations
The great majority of changes of residence are
bound up with other life processes, whether enforced
through persecution, repeated crop failure, impri-
sonment, or failure to pay rent or mortgage, or
chosen through change of or search for a job, search
for a better school catchment area, changed health
status, or on marriage. Location per se is rarely the
prime motivational factor, though amenities or
facilities can be important. But migration is part of
a class of processes that are bound up with social
position in society. This includes not just residential
stratification, but job and social hierarchies too. It is
no accident that much of the pioneering work on
social or occupational mobility was done by demo-
graphers (Hogben 1938, part II; Glass 1954; Blau
and Duncan 1967). Evolutionary demographers also
place great emphasis on the role of status and
hierarchy in mating and reproductivebehaviour
(Low 2000; Kaplan and Lancaster 2003).
The decision to move entails an ongoing evalua-
tion of alternatives, though this is not likely to be a
continuous preoccupation. The evaluation of current
position (job, housing, location, friendship network,
etc.) is almost inevitably better informed (by experi-
ence) than the evaluation of (multiple) alternative
positions (except for returnees) can be. Thus, usually
an informational asymmetry exists and we ought
therefore to pay greater attention to the perceptual
and risk-taking aspects of such behaviour (see
Section 3.2). How did pioneer migrants from Europe
to the USA or Australia evaluate the benefits of
such a move? They would have had much greater
certainty about possible push-factors (e.g., the Irish
potato famine) than about the trials and tribulations
and gains that awaited them if they survived the
journey. This kind of informational asymmetry
affects almost all choices about position (and many
other demographic choices too, for example, part-
nership and parenthood).
How do we deal with this in modelling and
understanding the positional behaviour of indivi-
duals (and some collectives)? What can we learn
from psychology and other relevant disciplines
about the nature of such decision-making? For
example, how relevant is the research on prospect
theory that suggests that decision-making is refer-
ence-dependent (and thus incompatible with ex-
pected-utility theory) and risk-averse concerning
gains, but risk-seeking for losses? (see Kahneman
2003 for a summary and further discussion in Section
3.2).
Personal ties: Family, kinship, intergenerational
and friendship links not just household structure
Co-residence in households is of considerable im-
portance for a reasonable fraction of (reciprocal)
transfers of time, money, and emotional support and
can have particular ramifications for the nurture of
children. However, key aspects of demographic
behaviour can be just as affected by such transfers
across household boundaries, through individual
transactions, public and private provision of welfare
and child services, and tax and benefit systems. We
cannot hope to understand the nature of demo-
graphic choice properly without looking at this wider
connectedness (see Seltzer et al. 2005).
These interlinkages have been made increasingly
complex and important by rising partnership fragi-
lity, especially for any children involved. Reports of
the necessity to examine the experiences of children
connected to up to eight grandparents or step-
grandparents (or occasionally even more) are no
longer implausible. Step-siblings and half-siblings
have also become fairly commonplace. Vastly differ-
ent arrangements of time, money, and nurture can be
involved.
Similar points can be made about transfers in old
age. There is some demographic research and much
more theorizing on old-age security as one rationale
for childbearing in traditional societies and on the
risks for those, especially widows, with no surviving
(and often co-resident) children (e.g., Cain 1986 and
the review by Das Gupta 1993). But this ignores the
lifetime or post-marriage reciprocal kinship and
friendship networks beyond the household that exist
162 John Hobcraft
in any long-standing (rural) community. Transfers of
care, emotional support, food, and other resources
across household boundaries are normative and yet
somehow ignored in much demographic and evolu-
tionary theorizing on these issues. If you do not look,
you do not find these links. They are rarely even
discussed or contemplated, let alone explored.
In developed societies too, inter-household trans-
fers, often reciprocal, play a large part in people’s
support networks and systems. This connectedness is
increasingly being recognized and incorporated in
survey instruments (e.g., the UNECE Generations
and Gender Programme or the US Health and
Retirement Survey; see also Seltzer et al. 2005).
There are important questions as to how much
differences in the balance between intra-household,
intra-family, other interpersonal, privately pur-
chased, and public provision of care, services, and
money have an impact on childbearing decisions,
partnership stability, well-being, and position. More-
over, it is possible that the source of such support
(e.g., public, private sector, or family) is of secondary
importance to its availability and accessibility.
Alleles, brains, and context: The ABC of
demographic behaviour
This section considers firstly some of the insights and
questions that arise from genetics for demography,
especially from behavioural genetics and taking
account of the shift towards measured genes. Sec-
ondly some of the relevant research relating to the
brain, mind, and endocrine system is reviewed, with
particular emphasis on affective neuroscience and
selected developments in behavioural economics.
Thirdly, it considers the wide range of contexts that
exert external influences on the person. Finally there
is a brief discussion of the importance of bringing
these elements together in comprehensive analyses
that try to elicit information about pathways and
feedbacks from evolutionary origins, through genet-
ics and the neuroendocrine system and their inter-
plays with context or environment.
It is essential to make clear that any apparent
separation of pathways within the person from the
processes outside the person is an expositional
artefact. Much of what I have to say will emphasize
the growing awareness of the critical importance of
interplays between the person or phenotype and
external or ‘environmental’ influences and of feed-
backs, interactions, and correlations. Gene expres-
sion can be determined by such feedback, frequently
from the external environment (for a clear account
see Chapter 9 of Rutter 2005). Evidence is beginning
to accumulate that specific variations (polymorph-
isms) in alleles substantially condition sensitivity to
environmental stress (see Caspi et al. 2002, 2003;
Johnson and Crow 2005; and, for a useful and
readable summary, Ridley 2003). (An allele is an
alternative form of a gene at a specific site (or locus)
on the chromosome (or genome).) There is also
growing evidence that external stimuli evoke endo-
crine responses that can bring about lasting, but not
necessarily permanent, changes in brain structure
(LeDoux 2003). The deep and unresolved issues
concerning the interplays of evolution, free will, and
instinct in cognitive processes (Dennett 2003) and
some of the work on decision-making heuristics will
also feature (Brocas and Carrillo 2003, 2004). Least
attention will be paid to reproductive biology,
because this is the area already most familiar to
many demographers (see Cameron 2003).
Genetics and demographic behaviour
This section reviews selected issues in behavioural
genetics and its link to demographic behaviour (a
very accessible general account of many of the issues
covered is provided in Rutter 2005). The first part
covers quantitative behavioural genetics, which is
about partitioning the variance in behaviour into
three components: genetic, shared environment, and
non-shared environment. These are ‘black-box’
approaches that tell us nothing about the pathways
involved. However, there has been some recent
work in demography using these approaches, and
this is briefly reviewed. This work has proved very
contentious (e.g., Vetta and Courgeau 2003) and
thus a careful discussion of the assumptions and
methods is warranted.
The second part of this section shifts attention to
molecular behavioural genetics, or behavioural geno-
mics, which is concerned with measured genes (from
DNA) and measured environments, and thus moves
beyond ‘black-box’ variance partitioning. A brief
review is provided of the demographic work in this
emergent area, which is especially rare in the
exciting field of gene environment interactions.
Since such work is rare, we again discuss some of
the methods and emerging research in related fields
in order to provide pointers for future demographic
research.
There has been some work using behavioural
genetic models to explore the extent to which
genetics plays a part in various aspects of demo-
ABC of demographic behaviour 163
graphic behaviour. Most of this work relies on
quantitative genetic (or ACE) models, using designs
such as twin or adoption studies that, in principle,
can separate the sources of variability in behaviour
into an Additive genetic component (A), a Common
or shared environment component (C), and a non-
shared Environment element (E) (see Plomin et al.
2000; Rutter et al. 2001; Rutter 2003a). The beha-
vioural genetic literature is most extensive in rela-
tion to IQ and mental health, especially
psychopathologies. Because I havereviewed the
studies that relate to fertility, divorce, and age at
first intercourse at some length elsewhere (Hobcraft
2003), the discussion here will be limited to some of
the major underlying issues.
Those who are sceptical about the role of genes
can make a powerful case for the lack of genetic
influences only through studies that explicitly in-
clude a genetically sensitive design (Rutter et al.
2001). Moreover, it is not possible to demonstrate
unequivocal ‘environmental’ effects on behaviour
except through such designs, since the dual-inheri-
tance aspect of genetic and shared family environ-
ment otherwise confounds the two. Some ingenious
work is now taking place using identical twins to
demonstrate unequivocal ‘environmental’ effects
(see, for example, Caspi 2004). Moreover, as will
be discussed later, there is currently a major shift of
emphasis towards molecular behavioural genetics
(or behavioural genomic) modelling (see Plomin et
al. 2003a; Moffitt et al. 2005).
Before discussing some of the major issues that
need to be taken into account for behavioural
genetic models, it is worth clarifying some key
concepts that refer to the interplay between genes
and environment (or context). One key distinction is
between geneenvironment correlations, denoted
rGE, and geneenvironment interactions, denoted
GxE (for fuller discussion of the concepts and
measurement issues see Plomin 1994, Chapter 4;
Rutter and Silberg 2002). Further, three types of
rGE are distinguished: passive, reactiveorevocative,
and active. A passive rGE arises from children
receiving parental genotypes that also affect the
family environment created by the parent (e.g.,
harsh parenting that is genetically mediated by the
parental genes). An active rGE arises from the
person with the genotype seeking or creating en-
vironments that are conducive to their genotype
(e.g., choosing a partner or job compatible with their
own genotype). Evocative or reactive rGE arises
from others reacting to the person on the basis of
their genetic propensities (e.g., being chosen as a
partner by someone seeking compatibility with their
own genotype). It is harder to separate these three
types of rGE analytically than to make the con-
ceptual distinction between them (see Plomin 1994;
Rutter and Silberg 2002; Eaves et al. 2003). Lastly
geneenvironment interactions arise from geneti-
cally influenced individual differences in sensitivity
to specific environmental (or contextual) factors
(e.g., stressful events bringing about differences in
the incidence of depression according to a specific
polymorphism in the serotonin transporter gene,
Caspi et al. 2003).
Despite their manifest strengths, quantitative
behavioural genetic models do have a number of
limitations. The genetic component almost always
includes all geneenvironment interplays, and this
may overstate the direct role of genes, possibly
substantially (Rutter and Silberg 2002; see also
Eaves et al. 2003, for an approach to separating
out geneenvironment interactions and correla-
tions). The more homogeneous the population the
smaller will be the ‘environmental’ elements and
thus the higher the measured heritability (perhaps
accounting for the higher heritability of IQ among
high socio-economic status groups *see Guo and
Stearns 2002; Turkheimer et al. 2003). Geneenvir-
onment interactions can complicate this further
(Rutter and Silberg 2002). The ‘shared’ environment
is essentially the role of common experiences. There
is a large literature concerned with the evidence that
this fraction of the variation is small (Plomin and
Daniels 1987; Dunn and Plomin 1990; Maccoby
2000; Plomin et al. 2001). Concomitantly, the share
of variability attributed to the non-shared environ-
ment is often quite large, though this share includes
any residual unexplained variance, a fact that is not
always acknowledged (see Turkheimer and Waldron
2000).
The models depend quite heavily on an assump-
tion that children reared in the same family experi-
ence equal environments, but this assumption raises
a number of questions when it is applied to twin
studies (Rutter 2003a). The assumption often made
is that identical twins have more similar environ-
ments because they are genetically and physically
indistinguishable; this would lead to an understate-
ment of the genetic component. I am not aware of
any serious discussion of the extremely plausible
idea that twins, and especially identical twins,
actually try much harder than other siblings to
differentiate themselves from each other and
thus to shape their environments to be more
different (see Segal 1999; for an interesting and
relevant treatment of this issue in the context of IQ
scores see Feldman et al. 2000). This would be an
164 John Hobcraft
interesting example of a negative active gene
environment correlation (see Plomin 1994). More-
over, studies of twins reared apart and adoption
studies usually pay very little serious attention to the
issues of sample selection through selective place-
ment in higher-status environments (Kamin and
Goldberger 2002). This selective placement in
homogenous environments could account for the
genetic sources of variance in adoption studies being
overstated by about a third compared with the
general population (Stoolmiller 1999).
There have been a few quantitative behavioural
genetic studies of fertility, including some innovative
attempts to examine changes over time in the
variance components of the genetic, shared, and
non-shared environment of Danish twins (Kohler et
al. 1999; Rodgers et al. 2001a,b; Kohler and Rodgers
2003), though the interpretation and instability of
their results has been questioned (Hobcraft 2003). It
is, of course, unlikely that any heritability would
remain in fecundity or in other fitness-related traits,
so that we can be reasonably certain that any ‘black-
box’ genetic heritability components are attributable
to fertility-related behaviours (Hobcraft 2003; Rut-
ter 2003a).
Behavioural geneticists have also provided a
couple of studies examining variance components
for divorce (McGue and Lykken 1992; O’Connor et
al. 2000), though McGue and Lykken ignore incon-
venient elements in their findings (for example, for
both men and women, MZ (identical) twins show a
lower overall correlation in risk of divorce than do
DZ (non-identical) twins) and selectively stress
results that do give some indication of genetic
heritability.
It is perhaps surprising that demographers have
not made fuller use of the genetically informed
designs of some major US longitudinal surveys (e.g.,
the NLSY studies, AddHealth, and the Wisconsin
Longitudinal Study), all of which could have been
used for quantitative behavioural genetic modelling,
rather than solely as a way of removing sibling or
other similarities through fixed-effects models (for
exceptions and a description of some of the pro-
blems with NLSY, see Rodgers et al. 1999; Rodgers
and Doughty 2000).
The very use of the term ‘behavioural genetics’
(when actually referring to evolutionary theorizing)
by Morgan and King (2001) in the context of fertility
behaviour led to a lively exchange (see Capron and
Vetta 2001; Kohler 2001; see also the comments by
Rutter 2003a and a broader attack on the use of such
models in demography by Vetta and Courgeau
2003).
Molecular behavioural genetics
The goal should be to identify the pathways through
which genes work or interplay with the ‘environ-
ment’, rather than to use ‘black-box’ models that
simply partition the variance. The exploration of
these pathways has been made possible by advances
in molecular biology, although the process can be
very complex and time-consuming (Plomin and
Crabbe 2000; Risch 2000; and Rutter 2003a in the
context of fertility behaviour). It is likely that the
role of genes in most complex behaviours that are
not pathological will result from an accumulation of
small effects over several genes, rather than from a
large effect over a few genes (Plomin et al. 2003a).
Increasingly the availability of microarrays or ‘gene
chips’ (Lockhart and Barlow 2001; Carpenter and
Sabatini 2004) and new methods of analysis (Butte
2002) make the search for multiple genetic markers
faster, cheaper, and more feasible. Moreover, there
are already clear indications that major longitudinal
demographic surveys will collect DNA, making such
molecular genetic analysis possible (e.g., in the UK
both the 1946 and 1958 birth cohort studies have
collected genetic material).
A few molecular genetic analyses related to
demographic behaviour have already been under-
taken, although the links are correlational and the
pathways and processes involved remain unex-
plored. One study has shown an association between
multiple marriages and the 7-repeat allele of the
dopamine D
4
receptor gene (Rowe 2003), which is
also linked in some studies to ADHD (attention
deficit hyperactivity disorder; see Faraone et al.
2001, 2005; Thapar 2003) and to novelty-seeking or
risk-taking behaviour (see Keltikangas-Ja¨rvinen et
al. 2004 for evidence on geneenvironment interac-
tions). Other studies have begun to explore linkages
of the dopamine D
2
receptor gene and low fertility
for men (e.g., MacMurray et al. 2003) and of the risk
allele for G6PD-deficiency in females to poor
intrauterine growth and possible lower fecundity
(e.g., Gloria-Bottini et al. 2003). All of these early
findings require replication and longitudinal studies
are needed to explore geneenvironment interac-
tions more fully (see Moffitt et al. 2005). Ewbank
(2000, 2004) has worked extensively on bringing
demographic insights into the understanding of the
links of allelic variation in the APOE gene to
Alzheimer’s disease. There is already an extensive
literature on geneenvironment interactions in
health (see Shostak 2003; Hunter 2005; Johnson
and Crow 2005; Ryff and Singer 2005).
ABC of demographic behaviour 165
Several problems hinder this search process,
although significant progress is being made. Firstly,
most such searches treat the effects associated with
the various markers as being additive (i.e., as
conforming to the broader general linear model
without interactions, a practice that also plagues
much social and behavioural research). At present,
sample sizes and statistical procedures can identify
associated individual markers that account for about
1 per cent of variance (as good as many of our own
predictors) but it is anticipated that many genes will
account for smaller components of variation (see
Plomin 2003; Plomin et al. 2003a; Plomin and
Spinath 2004 provide an excellent account of the
issues and approaches in relation to IQ; Faraone et
al. 2005 provide empirical evidence with respect to
ADHD).
Secondly, there is emerging evidence for the
importance of genegene interactions (epistasis) in
many contexts, including the link of the APOE gene
to coronary artery disease (see Brodie 2000; Tem-
pleton 2000; Grigorenko 2003; Carlborg and Haley
2004). There is also accumulating evidence for
epistatic interactions without identifiable ‘main’
effects of the individual genes (Grigorenko 2003).
Thirdly, gene expression is often triggered by
events external to the phenotype and there is
much concern among researchers about the impor-
tance of geneenvironment interactions and corre-
lations (Rutter and Silberg 2002 on emotional and
behavioural disturbance; Rowe et al. 1999, Guo and
Stearns 2002, and Turkheimer et al. 2003 on IQ;
Reiss 2000 on adolescent development). Most ge-
netic screening efforts do not have good measures of
these external factors (strictly external to the
genome, but usually in this context external to the
phenome or person).
Some of the most compelling evidence to date for
geneenvironment interactions at the molecular
level comes from the Dunedin study. Firstly, a
genotype conferring high levels of expression of
the neurotransmitter-metabolizing enzyme mono-
mamine oxidase A (MAOA) appears to moderate
the effects of child maltreatment on the subsequent
development of antisocial behaviour (Caspi et al.
2002). Secondly, individuals with one or two copies
of the short allele of the 5-HTT promoter poly-
morphism (in the serotonin transporter region) are
more likely than those homozygous for the long
allele to show depressive symptoms and to experi-
ence diagnosable depression, and suicidality follow-
ing stressful life events (Caspi et al. 2003). The latter
finding was guided by the role of serotonin reup-
take-inhibitor drugs in treating depression (provid-
ing a ‘candidate gene’) and is more plausible as a
consequence of this known link. A very helpful
discussion of the steps required to establish interac-
tions between measured genes and measured envir-
onments is provided by Moffitt et al. (2005), who
also refer to replications of these studies. A third
study from the same team has shown that cannabis
users with the COMT valine allele were more likely
than users with two copies of the COMT methionine
allele to exhibit psychotic symptoms (Caspi et al.
2005a). Helpful reviews of emergent research on
geneenvironment interactions in physical health
are given by Johnson and Crow (2005).
Demographers potentially have much to contri-
bute to the process of teasing out or replicating
molecular biological measured-gene-by-measured-
environment interactions in prospective population
studies using representative samples that collect
DNA. Indeed, Kohler, Yashin, and Vaupel have all
already contributed to the development of the
methods of behavioural genetic modelling (Tan et
al. 2003, 2004; Rodgers and Kohler 2005). And this is
likely to happen because our knowledge of (and
some ownership of) important population-based
longitudinal studies provides useful leverage and
we have a long record of engaging with the
biosciences. However, as Moffitt et al. (2005) stress,
the search for gene effects and especially for gene
environment interactions can be an arduous and
demanding task that requires insights into the
probable underlying biologically mediated path-
ways.
Unlike behaviour, experience, or attitudes, on
which retrospective information is often difficult or
impossible to collect, the invariant nature of DNA
permits collection at any point in time. On the other
hand, there are reasons to suppose that some
processes involve gene expression at particular
developmental stages of the life course (for a
discussion of the issues see O’Connor 2003a; for an
example of testing for such interplays see Rutter et
al. 2004). Thus some attention needs to be given to
evidence that might suggest that geneenvironment
interactions for some behaviours occur at a particu-
lar developmental stage only.
Brain, mind, and endocrine systems
In addition to engaging with behavioural genetics,
demographers have much to gain from knowledge
of and interaction with neuroscience, cognitive
and affective psychology, and with behavioural
166 John Hobcraft
economics. Demographic behaviour usually entails
choices and our understanding of choice processes
will be fatally incomplete if we ignore developments
in these fields. Moreover, the bonding processes
involved in both childbearing and childrearing and
partnership or mating behaviour clearly involve
lasting, though not necessarily permanent, changes
in the brain.
This section begins with a discussion of selected
findings from affective neuroscience, paying parti-
cular attention to a series of interrelated animal and
fMRI human studies on bonding and mating beha-
viour. The discussion illustrates how engaging with
such research can help in selecting ‘candidate genes’
that can then be explored using behavioural geno-
mics. The key role of neurotransmitters in human
behaviour is stressed.
The second part of this section covers material
drawn from behavioural economics. Again there has
been very little demographic research in this area,
except some work on mating heuristics. The section
mainly aims to draw attention to a few areas of
research on behavioural economics that seem ripe
for demography to engage with, including the
evaluation of decision heuristics, prospect theory
and loss aversion, and framing effects.
Affective neuroscience
We should be able to secure insights into mating and
reproductivebehaviour from research in affective
neuroscience (Davidson et al. 2003; see also Pank-
sepp 1998, especially the chapters on ‘The Varieties
of Love and Lust: Neural Control of Sexuality’ and
on ‘Love and the Social Bond: The Sources of
Nurturance and Maternal Behaviour’). Since much
of the research in neuroscience is based on animal
studies we also need to take account of the inter-
plays between innate systems and ‘free will’ and the
likelihood that these interact and feed back in
complex ways through evolutionary (see Dennett
2003), developmental, and short-term features of
brain structure and response (e.g., links between the
amygdala and the pre-frontal cortex for short-term
interplays*LeDoux 2003). Evidence is also accu-
mulating for lasting synaptic changes that result
from stimuli, including emotions, from outside the
person (e.g., LeDoux 2003, who makes the bold
claim that ‘we are our synapses’); and that brain
plasticity continues well into old age (Stern and
Carstensen 2000). A superb and insightful account
of the role of genes in the development of the brain
is given by Marcus (2004).
The aspects of brain structure that demographers
are most familiar with are those linked to sexual
dimorphism. Udry’s (1994) controversial PAA Pre-
sidential address or his even more controversial
article (Udry 2000) and the heated exchanges that
followed in the American Sociological Review (Fire-
baugh 2001; Kennelly et al. 2001; Miller and Costello
2001; Risman 2001; Udry 2001), are an attempt to
produce a biosocial theory of gender. Sexual di-
morphism also plays a significant role in much
evolutionary theory on partnership and reproductive
strategies (Diamond 1997; Low 2000; see also Zuk
2003 for a challenging and wide-ranging account)
and more implicitly in economic theory on fertility
(Becker 1991; Lam 2003). Key to the emergence of
sexual dimorphism is the role of testosterone,
mediated by aromatase to create the oestrogen
that masculinizes the brain and mediated by 5-
alpha-reductase to create the dihydrotestosterone
that masculinizes the body (Panksepp 1998; Schulkin
1999). Some of those neuroscientists who work
solely on animal studies forget that humans (and
other primates) have much more developed frontal
lobes than other species and are thus much more
likely to modify innate tendencies by exerting
control (applying ‘free will’). That mistake is espe-
cially evident in attempts to understand reproduc-
tion (e.g., Simerly 2002, who entitles his review
‘Wired for Reproduction’). There is little doubt that
sexual dimorphism can result in exquisite mechan-
isms that relate sex and reproduction (Cameron
2003), but there seems to be more evidence that
humans (and other animals) have a basic need to
have sex rather than to reproduce, though a basic
need to nurture is also identified (Panksepp 1998;
for different perspectives on this issue see Hobcraft
and Kiernan 1995; Potts 1997; Foster 2000; Morgan
and King 2001; Hobcraft 2003; Worthman 2003).
Some evidence is emerging from animal studies,
especially from contrasts of monogamous prairie
voles with promiscuous montane voles (Panksepp
1998, Chapter 12; Young 2003) about the neuroen-
docrine bases of monogamy (Young et al. 2002)
and pair bonding (Curtis and Wang 2003). For
female prairie voles, oxytocin released during copu-
lation acts on the oxytocin receptors in the brain to
induce lasting pair bonding and key elements of
parental behaviour. For male prairie voles the
release of vasopressin during orgasm similarly acts
on vasopressin receptors to produce lasting bonding
and parental behaviour. These results have been
fairly thoroughly substantiated using a variety of
ABC of demographic behaviour 167
techniques. Differences among a wider range of vole
species in social organization have also been linked
to differences in patterns of brain-receptor binding
of oxytocin and vasopressin. Other studies of rats,
sheep, and hamsters also suggest important roles for
oxytocin and vasopressin in maternal imprinting
(Numan and Insel 2003; Insel and Fernald 2004).
Thus there seem to be reasonable grounds for
proposing that studies of bonding and mating
behaviours in human populations should explore
links to the allelic variation in the markers for
oxytocin (OXTR; 3p26.2) and vasopressin (AV-
PR1a; 12q14-q15) receptors. Oxytocin and vasopres-
sin receptors are particularly dense in the prelimbic
cortex and nucleus accumbens, regions of the brain
that are also involved in the mesolimbic dopamine
reward pathway, suggesting a further role for dopa-
mine D
2
receptor (DRD2; 11q23) markers (Insel
and Young 2001; Young et al. 2002; Insel and
Fernald 2004). This suggestion is predicated on it
being easier to explore these issues for human
populations through the genetic markers that code
for the receptors than through direct observation of
the brain by fMRI (and certainly not through the
invasive approaches used in animal studies). Differ-
ences in relevant alleles for males and females
encoding for these receptors (AVPR1a, OXTR,
and DRD2) would thus be ‘candidate genes’
for the study of sexuality, bonding, partnership
breakdown, and parenting. For the human male,
sexual arousal leads to a short-term peak in blood
plasma levels of vasopressin, whilst ejaculation is
associated with a short-term increase in plasma
arginine-vasopressin (Murphy et al. 1987; as adapted
in Panksepp 1998). I have not found evidence
showing that these neurotransmitters bind to rele-
vant receptors in the brain to promote bonding in
humans, though it may exist. However, one twin
study of self-reported infidelity of females and
number of sexual partners found no evidence of a
link to the vasopressin receptor, AVPR1a (Cherkas
et al. 2004).
Other tantalizing evidence is beginning to emerge
on the link between opioid reward systems in the
brain and social attachments. Reward systems are
likely to be important in feedback mechanisms that
establish lasting synaptic responses to a partner or
child involved in long-term nurturance or pair
bonding. Using fMRI, Bartels and Zeki (2000)
examined responses in the brains of 17 subjects
who were ‘deeply in love’ to photographs of the
loved one and of other friends of the same sex. They
found that differential increased brain activity when
viewing the photograph of the loved one compared
with that of the friend was, perhaps surprisingly,
restricted to very few areas. Bartels and Zeki
conclude: ‘It is however striking that studies of
cocaine-induced and mu-opioid agonist-induced eu-
phoria have shown increased activity in foci that
seem to overlap with all foci activated in our study:
the anterior cingulate cortex, the insula, the caudate
nucleus and the putamen. This suggests a potentially
close neural link between romantic love and eu-
phoric states’ (p. 3833).
Bartels and Zeki (2004) have also carried out a
similar study comparing neural responses of mothers
to photographs of their own children, another
known child, an unknown child, their best female
friend, and a female acquaintance (they were also
shown photographs of their partners, but the results
of this are not reported). There was a considerable
overlap with the romantic love study in several brain
activation regions, but some differences too. Inter-
estingly, brain activity related to ‘romantic’ and to
‘maternal’ attachments overlapped with sites that
are rich in oxytocin and vasopressin receptors,
although one such area (the periaqueductal (central)
grey matter) was linked to maternal but not roman-
tic love (Bartels and Zeki 2004). These results seem
to tie in fairly well with those from the animal
studies discussed earlier, although the regions of the
brain involved differ somewhat, possibly suggesting
that different stimuli (visual, by design for the
Bartels and Zeki studies and the olfactory bulb in
the study of the prairie vole), whilst acting through
the same neurotransmitters, operate on different
specific brain sites. In both the animal studies and
the human brain scans, there is at least some
evidence for the roles of vasopressin and oxytocin,
as well as of the dopamine reward system, through
DRD2 pathways.
It is not yet clear how the short-term responses
observed by Bartels and Zeki for individuals for
whom an attachment already existed and for whom
there must have been some lasting change in brain
structure (otherwise there would be no long-term
bond and response to a photograph of a specific
child or partner), relate to the animal studies in
which it is the bonding itself that is the response, one
that induces lasting changes in the olfactory system
for voles, but relies on visual cues for mammals,
including sheep (Insel and Fernald 2004).
Perhaps we shall soon see emerging evidence from
brain scans of ‘happily’ married couples in long-term
relationships that have lasted beyond the first burst
of romantic love and of couples undergoing separa-
tion or divorce, which may give us greater insights
into the neural pathways involved in attachment and
168 John Hobcraft
partnership breakdown (see also Diamond 2004
on the distinctions between romantic loveand
sexual desire). Moreover, longitudinal studies using
appropriate scanning techniques may provide a
better understanding of whether there are identifi-
able lasting changes in brain structure connected
with bonding.
One other key theme of relevance to sexuality,
partnership behaviour, personal ties or connected-
ness, and parenthood is the apparent need to nurture
or care (in this context see Foster 2000; Hobcraft
2003). Nurturance or care is seen as one of the core
emotional systems (Panksepp 1998, 2005; Taylor
2002; Numan and Insel 2003). The reciprocity
involved in such interplays is also captured by the
‘core social motive’ of ‘belonging’ (identified by
Fiske 2004 as having primacy among her five core
social motives for behaviour, the others being under-
standing, controlling, enhancing self, and trusting).
An interesting attempt to integrate human bonding
processes from their possible evolutionary origins,
through neural pathways and onward through their
psychological elements is given by Miller and
Rodgers (2001).
Behavioural economics
A major source of recent and exciting developments
has been the interaction between psychology and
economics, including behavioural economics (see,
for example, the collections of readings in Brocas
and Carrillo 2003, 2004; Camerer et al. 2004; see also
Glimcher 2003). Because this burgeoning field is too
large to cover fully, some topics that are worthy of
further exploration by demographers will be selec-
tively discussed, with a particular emphasis on work
that is concerned with choice, especially some recent
linkages to neuroscience.
Much demographic behaviour is about choices
made under constraints: to enter a partnership, to
reproduce, to migrate, or to achieve well-being (for a
pioneering attempt to get demography to engage
with decision-making, see Burch 1980). In making
such choices people often use heuristics or intuitive
judgements since ‘rational models are psychologi-
cally unrealistic’ (Kahneman 2003, p. 1449). Kahne-
man and his long-term collaborator Tversky played
an extraordinarily influential role in demonstrating
that many elements of standard neoclassical rational
choice models were unrealistic, including the use of
and biases in decision heuristics, prospect theory and
loss aversion, and framing effects on choice (see, for
example, Kahneman’s 2003 revised Nobel lecture for
a useful summary).
Gigerenzer et al. (1999); see also Todd and
Gigerenzer 2000 for a lively discussion) place great
emphasis on the effectiveness of ‘simple heuristics
that make us smart’ or ‘fast and frugal decision
making’. Of possible interest to demographers are
the two attempts contained in this work to apply
simple simulated heuristics to mate search (Blythe et
al. 1999; also Todd and Billari 2003; Todd et al. 2005)
and to parental investment (Todd and Miller 1999),
though the simulations rely on highly simpli-
fied evolutionary theory. There is a sharp distinction
between the two approaches to decision-making
heuristics: Gigerenzer et al. try to show that these
heuristics work well, whereas Kahneman
and Tversky, in a treatment that is more careful
and thorough, demonstrate some of the failings and
biases of heuristics in addition to their power and
accuracy (see Gilovich et al. 2002; Kahneman 2003).
If we are to make real progress in understanding
how demographic choices are made, we shall need to
engage with this work. For example, there is a
potential for taking account of prospect theory
concerning a greater aversion to losses than to risk-
seeking preference for gains (Tversky and Kahne-
man 1992; Usher and McClelland 2004). It would be
fascinating to explore these domains for partner
choice, reproductive choice, and migration decisions,
where there is a clear informational asymmetry and
choice under uncertainty.
Another topic worthy of more exploration by
demographers is related to choices about timing of a
benefit, known as intertemporal choice in the
relevant literature (Loewenstein et al. 2003). There
is evidence that individuals differ in their propensity
to postpone gratification or in discount rates for
time, and thus in time perspectives or decision-
making horizons. Moreover, recent work has linked
delayed gratification to separate neural systems
(McClure et al. 2004), suggesting that immediate
rewards are evaluated by parts of the brain different
from those that deal with delayed rewards. Related
work discusses the roles of ‘hot’ or emotional
processing and ‘cold’ or rational processing and the
probable linking systems within the brain to deal
with trade-offs between the two systems (Metcalfe
and Mischel 1999; Mischel et al. 2003; also more
generally LeDoux 2003). A better understanding of
the processes underlying future discounting is also
emerging (Trope and Liberman 2003). Neurobiolo-
gical links are also usefully discussed by Manuck et
al. (2003), who provide a very clear discussion of the
evidence and probable pathways for an important
ABC of demographic behaviour 169
mediating role of serotonin and impulse control in
making choices about timing; this in turn links to
recent findings on the role of serotonin in increasing
trust (Kosfeld et al. 2005), since delayed gratification
clearly involves some trust that the gain can be
realized.
Choice about the timing of a benefit is of
relevance to demographers’ understanding and as-
sessment of early childbearing. For example, the
need for immediate gratification without time dis-
counting that is probable among deprived mothers
who start childbearing early may help us to under-
stand the qualitative work of Edin and Kefalas
(2005) and also relate to the ‘nothing to lose’
hypothesis advanced and tested by Harris et al.
(2002) in the context of risky behaviour in adoles-
cence. It is also of clear value in trying to assess
variation in how far and how much mid-term
security considerations play a part in decisions about
becoming a parent (Hobcraft and Kiernan 1995).
Choice about the timing of a benefit has been
explored in the context of health behaviours (Chap-
ters 1316 in Loewenstein et al. 2003). Some
discussion of hot/cold systems and partnership
maintenance is given by Mischel et al. (2003).
Demographers may also wish to consider the
speculations of Hobcraft (2003) and Rutter (2003a)
about the possible genetic predispositions for risk-
taking behaviour and the resulting pleiotropy (multi-
ple influences for one gene) that is likely to occur for
many aspects of reproductive behaviour (early child-
bearing, contraceptive failure, sexually transmitted
infection, partnership instability); the possible lin-
kages to (subsequent) disadvantage through job
instability and less informed choices may also be
relevant in understanding the consequences of
demographic behaviour. The neurobiological aspects
of risk-taking in this context are clearly likely to
matter too. In particular, the importance of the
development of the pre-frontal cortex in late adoles-
cence and its role in self-control may well be linked
to a wide range of risky adolescent behaviours,
including early sexual activity, partnership, and
parenthood (Steinberg 2004, 2005; for a populist
account see Strauch 2003). It is likely that decision-
making about the timing of a benefit and risky
behaviour are connected.
Context: Other persons
Evidently demographic behaviour is deeply bound
up with the person or phenotype interacting with
other persons. Children are born into families and
are reared by parents and other adults. Cohabitation
or marriage, reproduction, and sexual activity quin-
tessentially involve interactions with other persons.
Beyond these clear and directly relevant interperso-
nal demographic linkages, there are many other
potentially important contexts where the interplay
with other persons matters and may shape the
values, attitudes, health, and behaviour of the
phenotype and generate feedbacks within the per-
son, through synapses or geneenvironment inter-
plays. These important social contexts include family
and kinship networks, peer groups, friendship or
support networks, care and service providers, em-
ployers and workmates, members of the local com-
munity, and the personnel of a wide range of the
institutions of civil society. Yet research on demo-
graphic behaviour does not often address these
issues. A similar plea for much greater attention to
context is made by Seltzer et al. (2005).
Let us begin with the partnership dyad. Sex,
cohabitation, marriage, partnership breakdown,
and decisions about childbearing all involve both
members of the dyad and inevitably involve inter-
plays and behavioural adjustments. Both partners
bring to the union their phenotype at the time the
relationship is formed. Yet we typically know and
study only the most superficial aspects of these
characteristics, paying little attention to such diverse
and possibly important issues as the following:
previous partnership experiences (not just occur-
rence, but including relationship quality for exam-
ple), personality traits, peer and family pressures,
genetic predispositions, perhaps including the major
histocompatibility complex and possible links
through pheromones (e.g., Jacob et al. 2002; and
comments by Wedekind 2002 and reply by McLin-
tock et al. 2002; and from an evolutionary perspec-
tive Thornhill et al. 2003), etc. Of course, there is
interesting demographic work on partnership dyads,
including bargaining models (Bergstrom 1996;
Lundberg and Pollak 1996, 2003), and studies of
assortative mating (Kalmijn and Flap 2001).
Analyses of divorce or partnership breakdown
that simply examine the background of one partner
(e.g., whether they experienced parental divorce, or
their age at entry into the union) clearly omit all of
the background of the other partner and the
intimate and life-course interplays involved during
the partnership. This applies equally to the extant
attempts to examine the potential roles of genes and
behaviour in divorce. It is rare indeed to find careful
studies that begin to explore these aspects, though
see Robins et al. (2000) on how personality traits of
170 John Hobcraft
both partners are linked to relationship quality and
Jaffee et al. (2003) on an interesting interaction of
divorce consequences with the father’s antisocial
behaviour. Relationships evolveover time and much
of their changing character will be attributable to the
joint experiences and interpersonal interplays of the
two actors: this can involve shifting power relations,
patterns of intimacy, consequences of childbearing
and parenting, employment or health shocks, and
shocks from infidelity, among others (see, for
example, Karney and Bradbury 1995; Johnson and
Booth 1998; Rogers and Amato 2000).
Similarly, most decisions to bear and rear a child
involve two parents: this is a biological or genetic
certainty, but not necessarily a behavioural one
albeit predominantly so. Since reproduction is such
an essential component of evolution and of demo-
graphic behaviour, it is really quite surprising how
little attention is paid to the dyadic aspect of
childbearing decisions (though there are now a few
studies on this, for example, Thomson 1997). At the
biological level the fecundity of both partners
matters and genetic mismatches play a part in
inhibiting reproduction (Gangestad 2003). But we
need to move well beyond reproductive biology. In
particular we need to begin to pay much more
attention to how decisions on reproduction are made
and what roles are played in these decisions by
genes, brains, structural constraints, and interperso-
nal relationships. This undoubtedly requires major
research projects that involve behavioural geneti-
cists, neuroscientists, psychologists, social scientists,
and demographers at the very least. So does the
study of partnerships. A key requirement of progress
over and above this necessarily multidisciplinary
approach is the development of clever ways of
designing studies that recognize the dyadic nature
of these processes. We also need to sift the evidential
clues available in order to identify paths or frame-
works that seem likely to allow progress. For a useful
attempt to set out many of the issues involved for
human bonding see Miller and Rodgers (2001); see
also Miller et al. (2004) for a phenotype-level
discussion of a framework for pathways of fertility
motivation in couples.
Family networks, including both kin and partner
kin, are also linked with demographic behaviour,
though the pathways are often more diffuse. The
influence of parents or of parents-in-law on resi-
dence, on partnership formation, particularly for
arranged marriages, and on fertility behaviour is
claimed more often than carefully documented. The
roles of kin and partner kin in childrearing can also
be considerable. One of the issues that demographic
studies do not yet address is the relative importance
of genes and behaviour in such linkages. We have
virtually no evidence, for example, on the extent to
which the observed intergenerational linkages in
out-of-wedlock childbearing or in partnership break-
down are transmitted through nature, nurture, or the
interplay of both.
In an interesting extension of the role of social
networks, Felmlee (2001) examines their implica-
tions for ‘dyadic stability’. Other interesting work on
the roles of social networks in relation to demo-
graphic behaviour are given by Bearman and
Bru¨ ckner (2001) and Bearman et al. (2004) on
adolescent sexuality, by Rindfuss et al. (2004) on
fertility, by Kohler et al. (2001) and Behrman et al.
(2002) on contraceptive use, and by Watkins et al.
(2003) on HIV/AIDS.
Early and quite thoughtful explorations of com-
munity effects on child health and fertility-related
behaviours were hampered by the necessity to define
sample clusters as communities (Casterline 1985).
The important and oft-neglected issue of exploring
the interplays between levels in such multi-level
models was addressed by examining whether
mothers with different levels of education responded
differentially to access to services. More recently
analysts still have to face the conceptual difficulties
posed by having to equate sample clusters with
community (a particularly difficult assumption in
urban areas) but now do more to clarify the path-
ways and interplays likely to be involved between
different measures at the community level and
between these and measures of individual attributes
(e.g., Kravdal 2002, 2004; Whitworth and Stephenson
2002; Moursand and Kravdal 2003). There has also
been a rapid and related growth of interest in
neighbourhood effects, spurred in part by the avail-
ability of multi-level modelling packages (see
Brooks-Gunn et al. 1997; Harding 2003; Browning
et al. 2004).
Two interesting studies have explored multiple
contexts. Duncan et al. (2001) used the very rich
contextual information in the AddHealth Study to
explore upper bounds for the correlations of differ-
ent contexts or groups with adolescent development.
They found uniformly low correlations for school
and neighbourhood contexts, but some stronger peer
correlations although they rightly caution about the
degree of self-selection involved in the choice of
‘best friends’. The family correlations, which con-
flated the shared genetic and environmental compo-
nents, were consistently strong. It is a pity that they
did not go the further step of using a behavioural
genetic model to attempt partition of these within-
ABC of demographic behaviour 171
family (sibling) correlations, but they caution that
the differences observed between the MZ and DZ
twins suggested that instability was likely. Cook et al.
(2002) explored a range of these interpersonal
effects and their impact on early adolescent devel-
opment, looking at the joint influence of neighbour-
hoods, nuclear families, friendship groups, and
schools. Interestingly, the individual contexts each
appeared to show weak influence, but the joint
influence was large.
We still have a long way to go in conceptualizing
and measuring interpersonal contexts and their
probable paths of influence on demographic beha-
viour. The current uses of multi-level models (clearly
one useful tool) often suffer from a lack of con-
ceptual clarity about the levels and groups identified
and about the pathways likely to be involved,
especially the differential responses that are likely
to the group-level influences for individuals with
differing characteristics. Moreover, without identify-
ing measures at the higher levels of aggregation (and
this may well not be enough) it is not possible to
distinguish the influences arising from interpersonal
interplays from those arising from structures: is it
community or neighbourhood that matters; school
environment and teachers or fellow pupils; carers or
transfers (see Duncan et al. 2001; Cook et al. 2002)?
Most demographers could benefit from a close
reading of two classics on the topic of macromicro
interplays that did pay close attention to conceptual
issues and pathways: Blalock and Wilken 1979;
Coleman 1990; see also Cacioppo et al. 2000 in the
context of neuroscience).
Contexts: Structures, institutions, opportunities,
and constraints
There are also a large number of potential influences
on demographic behaviour that arise from social,
political, and organizational or institutional struc-
tures, rather than from interpersonal relationships,
although much of the influence of structures on
individuals can be and is mediated through inter-
personal relationships. These structural elements,
too, can operate at quite different levels of aggrega-
tion. One evident example, reported in the family
planning and health literature, is the role of provi-
sion and accessibility of services (for early examples,
see Casterline 1985). These services often impinge
most directly on the individual’s reproductive beha-
viour or health outcomes at a fairly local level, but
are shaped and constrained by issues as diverse as
national (and sometimes international or sub-na-
tional) policies, political will, supply chains, and
management structures.
In the context of health and well-being there are
important and only partially resolved questions
about how differing health systems and differences
in public/private mixes of health provision matter,
about the pathways and mechanisms through which
public health measures affect well-being, and about
the ways in which these structural features are
mediated by individual attributes, including beha-
viours, socio-economic status, and genetic predispo-
sitions (see Singer and Ryff 2001 for a useful and
thorough review of progress and the challenges
ahead). More broadly, potential is affected by
disease ecologies, welfare systems, labour markets
(often fairly localized), education and training
opportunities, cultures and norms, regulation, gov-
ernance, and human rights.
Partnership and parenthood are also influenced
by a variety of structures at differing levels of
aggregation: education and training make demands
that compete with family formation; housing mar-
kets shape and constrain choices; welfare regimes
and child service provision affect parenting decisions
and choices; gender, class, ethnic, and intergenera-
tional structures exert their impact; cultural pres-
sures and government interference in or support for
sexual and reproductive rights and choice all matter
too (see, for example, Esping-Andersen 1999, espe-
cially Chapter 4, on welfare regimes; McDonald
2000 and Neyer 2003 on gender; Van de Kaa 1987,
1994, 2004; Lesthaeghe 1989, 1995).
Cultures and social contexts influence much
demographic behaviour. The flourishing field of
anthropological demography pays close attention
to these issues (see Greenhalgh 1995; Kertzer and
Fricke 1997; Fricke 2003). An interesting approach
to integrating cultural and economic approaches to
fertility was proposed by Pollak and Watkins (1993).
Binmore (2005) addresses the issues of the emer-
gence and roles of culture much more broadly, using
game theory, and elaborates the enticing proposition
that cultures determine which game-theoretic equi-
librium solution is chosen in a particular society.
Other institutional factors have also received atten-
tion in the context of demographic behaviour (see,
for example, McNicoll 1980 for an influential study)
and Smith (1989) elaborated some of the theoretical
issues.
There are considerable difficulties in demonstrat-
ing and teasing apart these structural influences on
demographic behaviour. Firstly, as is clear from the
brief discussion above, there is a wide range of such
172 John Hobcraft
elements, each of which may have a small impact,
but these may accumulate to become a much larger
influence, partly through interplays. A simple ex-
ample is the potential interplay between school
hours and meal provision and normal hours of
work for decisions about becoming a parent. Sec-
ondly, many issues themselves cross-cut each other:
parenting decisions may be highly dependent on
child services being available, affordable, and acces-
sible, but may be unaffected by whether such
provision is from the public sector, the private
sector, or the family. Another illustration comes
from the recent activities of those European govern-
ments that are trying to raise fertility with one-off
cash incentives for having babies, payments that are
usually quite small compared with the real long-term
costs of rearing a child. Serious explorations are
urgently required into the differential responses to
be expected by income or socio-economic status, of
potential perverse incentives for risk-takers, and of
the unintended consequential burdens for the wel-
fare state. (Of relevance here is the discussion of
time discounting above and, for example, Harris et
al. 2002; Edin and Kefalas 2005.)
In order to make real progress in documenting
and disentangling such complexities we need clearer
mid-level theories or frameworks that help to shape
and structure data collection and analysis (see also
Seltzer et al. 2005). Moreover, since many of these
influences often do not vary much within a single
country, we shall have to use clever and fairly
descriptive approaches based on comparable infor-
mation to tease out their relative importance. The
UNECE Generations and Gender Programme con-
tains an important contextual component that
should enable some progress to be made in under-
standing many family-related behaviours by the
combination of prospective panel data with a con-
textual database for all of the participating countries.
But these topics are conceptually and analytically
difficult.
Progression of the person through the life course
Throughout the discussion so far, we have empha-
sized that genes, brain, mind, person, other persons,
and structures all interplay over time, both within
and across these domains. Understanding human
behaviour, including demographic behaviour, thus
demands attention to multiple dynamic processes
and involves many complex feedbacks and interac-
tions. As we progress in our understanding we shall
surely find that a whole series of ‘life packages’,
sequential chains, key precursors, and conditional
triggering or moderating events will be involved.
The key actor to be considered as the focus in this
study is the individual person or phenotype. Ulti-
mately, most human behaviour involves decisions or
choices made by individuals. As nicely put by Fiske
(2004), these individuals need to belong (and thus
interact with other persons), to understand (in order
to relate and to make choices more informed), to
control (their own lives and perhaps the interplay
with others and structures), to enhance themselves,
and to trust (other persons and institutions). Indivi-
dual capacities, traits, and attributes change through
the life course (Mortimer and Shanahan 2003)
involving continuous interplays and feedbacks
within the person and between the person and the
environment (Bateson and Martin 1999). Even
apparently fixed characteristics such as sex at birth
or race change their meaning and are mediated
through gender structures or discrimination accord-
ing to the life-history and temporal and spatial
context of the individual concerned. DNA is also
fixed, but gene expression often varies over time,
reacting to and shaping behaviour, experiences, and
the context or environment; such variations in gene
expression may also be heritable (known as
epigenesis*see Rutter 2005, Chapter 9); equally
brain structures remain plastic, although signifi-
cantly shaped by our genes (Marcus 2004). Thus, at
any one time, individuals bear the legacies of their
genetic inheritance, familial endowments, and past
experiences and these affect and constrain any
current choice or behaviour (e.g., Mortimer and
Shanahan 2003).
A great deal of emphasis in demographic research
is on either the current characteristics of the person
or what they were at the time of a recent event: for
example, income and other measures of socio-
economic status, housing status, marital status,
parity, age. Yet clearly the pathways by which this
status was reached (often referred to as trajectories
in the life-course literature) matter too. Does the
current socio-economic status reflect recent (or
longer-term) upward or downward movements?
These directional changes may have profound im-
plications for decisions about housing mobility,
partnership co-residence, or becoming a parent.
Some shocks that have received attention are those
resulting from (other) demographic processes: un-
planned babies, infant and child deaths, divorces,
and bereavements. Others involve the interplay with
unemployment or with the massive institutional
changes in the Central and Eastern European
ABC of demographic behaviour 173
(CEE) countries. Discovering whether and how far
the influence of such changes on behaviour is
different for people with different alleles on relevant
genes will need to be a prominent feature of the
research agenda in the future.
Some attention has been paid to attempts to
capture more lasting attributes: for example, human
capital, ‘permanent income’, or social class (usually
based on current or most recent occupation). The
proliferating set of concepts around cumulative
‘capital’, including wealth, human capital (Becker
1964), social capital (Coleman 1988), health capital
(Grossman 1972), and sexual capital (Michael 2004),
also reflect a greater attention to the person’s life
course. Other attempts to capture more lasting
characteristics have employed measures, however
imperfect, of the ‘big five’ personality traits (Extra-
version, Agreeableness, Conscientiousness, Emo-
tional stability or Neuroticism, and Intellect or
Openness to experience, see Costa and McCrae
1992; McCrae and Costa 2002), of IQ or ‘general
ability’ (Plomin 2003), and more recently the con-
cept of emotional intelligence (Goleman 1995) (see
Caspi et al. 2005b for a useful review on trait
stability). There is also a huge psychological litera-
ture on resiliency*the characteristics that can serve
to protect individuals experiencing risk from enter-
ing disadvantage or that can promote easier exit
from disadvantageous circumstances (Luthar et al.
2000; Rutter 2000, forthcoming; Luthar 2003). This
in turn relates to recent theorizing about social
policies intended to deal with social exclusion (Hills
2002; Hobcraft 2004). The mediating role of genes
and brains in resiliency is also becoming a topic of
interest (Curtis and Cicchetti 2003; Rutter 2003b;
Kim-Cohen et al. 2004). Serbin and Karp (2003,
2004) provide a useful summary on intergenera-
tional aspects of resilience and vulnerability.
Although all of these constructs, measures, and
theories are concerned with lasting features of the
person, all the features are in fact malleable. There is
ever growing documentation of brain plasticity, even
into old age (Stern and Carstensen 2000; Kolb et al.
2003; LeDoux 2003). The effects of serious disad-
vantage can be overcome and studies of the process
provide useful insights into biological programming
for development (as shown for Romanian orphans’
IQ by Rutter et al. 2004). Knowledge and skills can
always be accumulated. On the other hand, the
shocks of unemployment, bereavement, or partner-
ship breakdown can have short and long-term
impacts on well-being and happiness (Lucas et al.
2003; Layard 2005). Moreover, Sampson and Laub
(1993) and Laub and Sampson (2004) show how key
transitions into marriage or military service can act
as turning points in the life course.
Attention to these life-course legacies in the
context of demographic behaviour and with an
interdisciplinary focus is a rapidly growing field.
For example, Chase-Lansdale et al. (2004) brought
together demographers, economists, and psycholo-
gists to review a broad range of issues affecting the
potential for change across the life course and across
generations. Some good work is also being con-
ducted on the disentangling of the pathways to
health (see, for example, Hayward and Gorman
2004; Smith 2004; Case et al. 2005).
One of the main concerns of this paper is that of
how we move towards a better understanding of the
way in which experiences and contexts ‘get under
the skin’ to determine demographic behaviour,
acting through differing deep brain structures that
are affected by genes and differing patterns of gene
expression in response to external stimuli, and how
the differing legacies from endowments and experi-
ence shape interaction with and choice of contexts
(see Marcus 2004 for a very clear account of the
complexities of these interplays for early brain
development; see also Bateson and Martin 1999).
But one goal of science is to structure this
potentially huge set of legacies, current attributes,
and contexts, and to disentangle what really matters
for particular decisions or behaviour. To do so
requires sharper conceptualization and measure-
ment, a multidisciplinary approach, large-scale in-
vestment, and innovative analysis and modelling.
This is a great challenge and there is no simple
recipe for progress. It will require much effort and
some serendipitous or talented individuals to take
the bold steps required.
Conclusion
Ihave argued at some length that demographic
research needs to continue to move in the following
directions: to shift its focus towards the rich tapestry
of pathways, processes, and progressions; to tackle
the difficult and interesting problems of understand-
ing behaviour, rather than undertaking elaborate
description; to pay more attention to mid-level
theories or frameworks, including judgements on
what really matters; to look at mediating and
protective factors; to sharpen understanding of
processes and progressions involving, and distinc-
tions between, proximate, distal, and ultimate fac-
tors; to engage with genetics, neuroscience,
psychology, and behavioural economics; and to
174 John Hobcraft
explore the mutual interplays and feedbacks among
alleles, brains, and contexts in shaping demographic
behaviour.
One of the key judgements involved in working
through the relationships suggested as a priority for
investigation here is how to make real progress. In
exploring the links of DNA to demographic beha-
viour do we moveever further backwards from
demographic behaviour through proximate and then
just less proximate (and so on) factors, or do we
begin with the genome and explore forwards? Both
are probably necessary and will undoubtedly often
meet in the brain (Plomin et al. 2003b). The
forwards approach has been termed behavioural
genomics and a good description of the challenges
and issues is given by Plomin et al. (2003b).
The broad agenda set out here implies significant
shifts of emphasis in the way that we research
demographic behaviour. The emphasis on pathways
will entail collaboration with geneticists, neuroscien-
tists, and psychologists, since we require knowledge
about candidate genes, probable neural pathways,
and the underlying physiology and endocrinology.
But it is also important for these disciplines that we
collaborate with them, since the highly probable
importance of environmental factors triggering neu-
roendocrine responses among those that can cross
the brainblood barrier, and of interplays and
differential expression of these proteins and their
brain receptors and transporters for different alleles,
requires a deep knowledge of the key contextual
linkages too. Moreover, our substantive knowledge
about environmental associations may help in iden-
tifying pleiotropy. We all have much to gain from a
fruitful collaboration of this kind. Such connections
may help to move demographic behaviour into
greater prominence for neuroscientists, geneticists,
and psychologists. As Robert Plomin (2001, p. 1104)
has said ‘the genetics of behaviour is much too
important a topic to be left to geneticists!’
A further implication is the need for significant
improvement in our theories, measures, and data
sources relating to the individual and contextual
areas. For this it is essential to maintain and enhance
existing large-scale prospective panel studies, as well
as establish new ones, that make possible the study
of processes. Moreover, these studies need a major
cross-disciplinary investment, in order to make real
progress in breaking out of narrow disciplinary silos
and reaching some (tentative and revisable) con-
sensus on what really matters and on how to
measure complex processes and constructs simply
enough to make a broad-scale study workable with-
out losing focus and clarity. As those who have been
engaged in such cross-disciplinary endeavours will
readily admit, this process is a challenging one, since
individual disciplines always claim (often with some
justification) that their topic requires very detailed
measurement (e.g., components of income or per-
sonality measures). But these same researchers often
come out of interdisciplinary negotiations with a
much better understanding of the issues involved
and recognize the benefits of meeting the challenge.
Not only do we need complex prospective studies,
we also need to explore the possibilities for making
such studies more sharply focused on specific ques-
tions. We may not make much headway in under-
standing reproductive behaviour from ‘omnibus’
generic surveys that try to meet a very broad range
of needs, even though much useful work has been
done using cohort studies of various kinds. Rather,
we could benefit from studies with a clear and
explicit design and focus that address one issue.
An example would be the US Fragile Families Study
(Sigle-Rushton and McLanahan 2002), which has
drawn a sample very explicitly focused on families in
which the partnership was ‘fragile’ at the time of the
birth of a child. Hobcraft (2002) provides an
illustrative example of a design that might move
towards a better understanding of reproductive
choices. Of course, there is always a problem of
obtaining funding for more narrowly focused large-
scale studies.
There are a whole series of design issues that need
addressing for these specific studies. What is the
appropriate primary unit of observation: woman,
child, or dyad? How do we follow multiple family
members and trace changing circumstances of in-
creasingly complex parenting? At what levels or
from which groups do we need to obtain information
on interpersonal or structural contexts and which
ones matter for specific demographic behaviours?
How do we avoid sample selection and bias in
genetically informed designs (e.g., those used for
adoption studies, sibling studies, twin studies, etc.) or
do we need these designs at all in the post-genomic
era?
Not least among the challenges will be improving
our analytic methods (and borrowing them from or
working with those of a range of other disciplines).
The challenge of separating choice (or self-selection)
from structures and constraints (or social causation)
is an ongoing one (Caspi 2004; Moffitt 2005). Deal-
ing with endogeneity (often an intimate and key part
of the process that requires understanding and
one therefore that should not simply be controlled
away), path-dependence, and ‘life-packages’ is
difficult. In addition better conceptualization and
ABC of demographic behaviour 175
specification of levels of aggregation and of inter-
plays across these levels (both external to and within
the individual) is evidently required. Also difficult
are the specification and interpretation of interac-
tions and interplays (e.g., separating passive, active,
and evocative geneenvironment correlations, see
Plomin 1994) and geneenvironment interactions
(Rutter and Silberg 2002). Prospective or long-
itudinal studies are an essential component of this
endeavour, but the challenges of imaginative and
informed uses of such information are substantial
(see the illuminating discussion by Rutter 1994). The
availability of ever improving tools for multi-level
and for multi-event, multi-process modelling will be
helpful here, as will the use of psychology’s struc-
tural equation and behavioural genetic modelling
approaches. Nevertheless, these tools and models
are only as good for understanding demographic
behaviour as measurement and conceptualization
permit.
We also need to theorize more. The agenda for
disentangling the plethora of factors discussed in this
paper is truly daunting and cannot be progressed
without judicious simplification. This requires care-
ful evaluation of available evidence and some
innovative and speculative exploration of a variety
of potential pathways and processes, mainly through
empirical research but sometimes also through a
variety of theoretical and agent-based simulation
modelling approaches (e.g., Billari and Prskawetz
2003). Careful attention is also required to allow the
identification of candidate genes and biologically
plausible pathways (Moffitt et al. 2005). As with
most scientific endeavours, it will prove essential to
enable several groups to explore the same themes in
order to discover what really matters and permit
replication. The themes and more specific sub-
themes will address such questions as why do we
move, or enter a partnership, or become parents?
The Human Genome Project was a massive and
expensive collaborative undertaking and has con-
tributed hugely to the potential for research (Ca-
valli-Sforza 2005). The sharing of scientific
information permits relatively easy access to up-to-
date findings (Stein 2003). Major advances are now
occurring through the following bodies: the Com-
plex Trait Consortium (Members of the Complex
Trait Consortium 2003) on QTLs (quantitative trait
loci*see Plomin et al. 2003b); the International
HapMap Consortium (2003, http://www.hapmap.
org; see also Van den Oord and Neale 2004, and
Sklar 2005 for a discussion of whether and how
haplotypes help in behavioural genetic research); the
Human Epigenome Project (http://www.epigen-
ome.org), which is exploring the DNA methylation
that appears key to epigenetic feedbacks from the
environment to gene expression; and the Human
Proteome Organization (http://211.32. 65.137/hpp/
hppp.htm and http://www.hbpp.org), which is identi-
fying the means by which genes express the much
larger number of proteins in the body and brain than
there are genes and the functions of these proteins
(see also the Allen Brain Atlas *http://www.braina-
tlas.org).
The scale of investment in the human genome
project and its follow-ons will also be needed
soon for a human phenome project. There is a real
need to bring together talented interdisciplinary
teams working on the big issues of human behaviour.
Demographic behaviour is undoubtedly among
these big issues, since both survival and reproduction
(and the search for ecological niches) are essential
elements of evolution (which means biologists
should need little convincing) and policy makers
in both developed and less developed countries are
all too aware of the consequences of human
population movement, health, the family, and re-
production.
The daunting agenda outlined in this paper has
profound implications for the way we teach and
research. It requires refining into proposals for
specific projects, only a few illustrative examples of
which have been suggested in this paper. As stressed
throughout the paper, this major endeavour requires
interdisciplinary teams, progress in theory and
knowledge sharing, and attention to all parts of the
ABC (alleles, brains, and contexts) of demographic
behaviour, as well as to the person(s) engaging in the
behaviour we study. Not everyone in the field will
share my passionate belief that it is essential for
population studies to become an integrative science
of human demographic behaviour, engaging with
other disciplines along the lines outlined here. But I
shall be surprised if the integration of genomics and
neuroscience into the study of demographic beha-
viour is not more common within a decade than is
the attention paid to context today. In achieving this,
the whole field will have had to become more subtle
and focused in dealing with the complexities of the
interplays and feedbacks among alleles, brains, and
contexts.
Note
1 John Hobcraft is Professor of Social Policy and
Demography at the University of York. E-mail: jh511@
york.ac.uk
176 John Hobcraft
Acknowledgements
Work on this paper was facilitated through extended stays
at the Center for Health and Well-being, the Center for
Research on Child Well-being, and the Office of Popula-
tion Research at Princeton University, and the Demogra-
phy Department at the Australian National University.
Both universities provided a stimulating intellectual en-
vironment and access to libraries that covered genetics,
neuroscience, and psychology; my recent move to the
University of York has helped this process further, with
new colleagues John Hey and Andy Young providing
needed reassurance on revised sections of the draft. I am
deeply indebted to friends and colleagues far too numer-
ous to list, for their insights, knowledge, and support in
learning about the issues addressed in the paper over an
extended period. I have benefited from several extended
discussions with Kathleen Kiernan, Bob and Nancy
Michael, Nina Segre, and my many friends in Princeton,
especially over regular dinners with Sara McLanahan, Irv
Garfinkel, Anne Case, and Angus Deaton who provided
much help in clarifying my ideas. I have also benefited
from feedback in seminars at ANU and the Universities of
Chicago, Princeton, and Johns Hopkins, and from a day-
long discussion with Chris Bachrach, Jennifer Johnson-
Hanks, Hans-Peter Kohler, and Phil Morgan on parent-
hood issues whilst revising the paper. Finally, I should like
to acknowledge the valuable comments I have received on
the complete draft manuscript from Tom Burch, John
Bynner, Angus Deaton, Kathleen Kiernan, Steve Martin,
Bob Michael, Mike Rutter, Jackie Scott, and eight
anonymous referees.
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