Randy Thornhill

University of New Mexico | UNM · Department of Biology

The Evolution of Insect Mating Systems John Alcock and Randy Thornhill More than 30 years ago we wrote The Evolution of Insect Mating Systems. To be invited to comment on the current collection of chapters that update our book is both flattering and sobering—flattering because it is nice to think that we may have stimulated others to study insect m...

A growing literature shows that the features women find particularly attractive in men vary across the ovulatory cycle. Women furthermore appear to more frequently report attraction to men other than primary partners when they are fertile in their cycle than in the infertile luteal phase. Previous studies have shown that men are more vigilant of or...

The parasite-driven-wedge model provides a mechanism of parapatric speciation (the evolution of adjacent species across the range of an ancestral species without allopatric separation). Regionally localized coevolutionary races between para-sites and their hosts result in three locally adaptive antiparasite behaviors: mating and other social prefer...

Comparative methodology is controversial in biology and the related field of research on behavioral and psychological traits across human cultures. We critically examine this controversy. We argue that the widely held opinion of non-independence among historically-related cultures and species errs by not recognizing and incorporating into research...

Women's sexuality, unlike that of most mammals, is not solely defined by sexual receptivity during the short window of fertility. Women demonstrate extended sexuality (in which they initiate and accept sexual advances outside of the fertile phase) more than any other mammalian female. In this light, surprisingly little research has addressed the fu...

This revised version of the figure was supposed to have been published with the manuscript but was overlooked by the editorial office.

Women can conceive an offspring about 6 days of every ovulatory cycle and yet are sexually active throughout the cycle. But why? And are women's sexual interests nonetheless sensitive to hormonal changes across the cycle? This chapter explores these issues, and emphasizes several themes: (a) Women appear to have retained a form of fertile-phase est...

This chapter discusses the theory and research on sexually antagonistic coevolution, considers human sexuality in light of major sexual conflicts, and describes recent research on psychological changes across women's cycles. The selective pressures that led to concealed ovulation and extended female sexuality in humans have been debated for more th...

Over the past 15 years, extensive research has documented that estrus in women is present, not absent due to evolutionary loss, as scholars concluded erroneously by the middle of the last century. Estrus in women is a set of sexual preferences, manifested in the fertile window of the menstrual cycle, for mates with traits that connote male phenotyp...

The human microbiome is considered crucial for human livelihood. As such, the transmission, inheritance, and maintenance of the human microbiome across generations must be the result of direct natural selection favoring the adaptations involved. Or is it? It’s possible that microbiome inheritance results incidentally from social interactions and ot...

The parasite-stress theory of sociality is a new perspective on human social psychology and behavior. As an ecological and evolutionary theory of values or core preferences, it applies widely across domains of human social life and human affairs. We explain and expand the theory, and review a number of findings its application has discovered. Funda...

Parasite adversity was an important source of Darwinian selection in human evolutionary history because parasites selected for a diversity of human behavioral parasite-defenses in addition to the numerous defenses provided by the classical human immune system. We argue for a broader view of behavioral immunity than has been emphasized recently. We...

http://link.springer.com/book/10.1007%2F978-3-319-08040-6 This is link to the ebook where chapter abstracts can be read, front matter can be downloaded free, and other chapters may be purchased. Also i understand that if one's institution has a Springer subscription the whole book can be downloaded as mycopy for 25 US dollars but I am not yet fami...

Evidence across countries indicates that as parasite stress increases, so does introversion and closed-mindedness to new experiences. Also, the number of nonzoonotic human infectious diseases predicted significantly cross-national differences in the personality traits; the number of zoonotic parasitic diseases did so only marginally at best. A foll...

The parasite-stress theory of values offers new perspectives and research directions for the study of interpersonal violence, and provides a theoretical and empirically synthetic foundation that promises to be more encompassing than those used by previous interpersonal-violence researchers. Evidence indicates that parasite stress may be the stronge...

The parasite‐stress hypothesis of economics proposes that variation in infectious disease across regions causes variation in economic productivity by three proximate causes. (1) Infectious diseases cause morbidity, reducing people’s capability to produce. (2) Parasite stress evokes people’s values, which, in turn, cause regional economic parameters...

The countries of the world vary in their position along the autocracy–democracy continuum of governance. We hypothesize that the variation in values pertaining to the autocracy–democracy dimension arises fundamentally out of human species-typical psychological adaptation that manifests contingently, producing values and associated behaviors that fu...

We treat the scientific procedures and assumptions used throughout the book. The scholarly study of aesthetic judgments, including those about the attractiveness/unattractiveness of values, initially arose as a branch of philosophy. We criticize the philosophical method as a way of knowing the causes of values. The scientific method, developed in p...

Researchers have studied extensively regional variation in religious commitment and participation (religiosity). Such research, whether based on economic theory or evolutionary theory, emphasizes the high costs to individuals of religiosity. We have offered a new hypothesis of religiosity based on the parasite-stress theory of values. It relies on...

The parasite-stress theory of values/sociality is presented in detail. Humans have two immune systems: the classical physiological, cellular, and tissue-based defense system and the behavioral immune system. Only recently has the latter been investigated in detail; it is comprised of two parts: (a) psychology and behavior for infectious-disease avo...

This chapter documents the applicability of the parasite-stress theory of values to the frequencies of occurrences of the major types of within-nation intergroup conflict across contemporary countries: civil wars, non-state wars (intrastate wars in which warring groups do not include the government of the state), and coups and revolutions. Collecti...

The parasite-stress theory of sociality includes a theory of biodiversity: the parasite-driven-wedge model. Regionally localized coevolutionary races between parasites and their hosts result in three anti-parasite behaviors: preference for in-group affiliation and interaction, out-group avoidance (xenophobia), and philopatry. These three behaviors...

The parasite theory of sexual selection, originated by Hamilton and Zuk in 1982, is a subcategory of the more general and encompassing parasite-stress theory of sociality. Across indigenous societies, parasite-stress is correlated positively with the degree of polygyny. This is expected because high parasite stress generates high variation in the p...

The overall goal of our book is to create a synthesis or unity, based on the parasite-stress theory of values/sociality, of many topics that traditionally have been viewed and studied as distinct. The book presents the utility of the parasite-stress theory for unification of areas of research and knowledge ranging from parasitology, immunology, mor...

The particularistic method of cultural analysis relies on a region’s specific cultural history to explain why the region’s culture is the way it is. The particularistic method assumes incorrectly the popular view that culture is passively accepted by future generations. A very different perspective on culture sees people as evolved cultural strateg...

As predicted by the parasite-stress theory of values, variation in parasite stress correlated with collectivism–individualism across nations, USA states, and indigenous societies. In regions with high adversity of infectious diseases, human cultures are characterized by high collectivism, whereas in regions of low parasite stress cultures are highl...

The large scientific literature on human values produced prior to the recent publication of the parasite-stress theory of values is reviewed and analyzed. The major causal frameworks in that literature—climate and wealth—are not alternatives to the parasite stress of values—they are complementary, proximate causes of values. The parasite-stress the...

This book develops and tests an ecological and evolutionary theory of the causes of human values-the core beliefs that guide people's cognition and behavior-and their variation across time and space around the world. We call this theory the parasite-stress theory of values or the parasite-stress theory of sociality. The evidence we present in our b...

Women in the fertile phase of their menstrual cycle show an enhanced sexual preference for masculine expressions in behavioral, morphological and scent traits. These masculinity preferences may be associated with testosterone (T) levels in males and hence connote male quality as a sire. Thus, a scent preference of fertile-phase women for T is predi...

Hackman & Hruschka (2013) have criticized our studies across USA states of the cultural variables homicide, child maltreatment, religiosity, and family ties. We published analyses of these variables in relation to parasite adversity in Thornhill & Fincher (2011) (homicide and child maltreatment) and Fincher and Thornhill (2012a, 2012b) (religiosity...

Fast life histories, not pathogens, account for state-level variation in homicide, child maltreatment, and family ties in the U.S. Evolution and Human Behavior, 34,118–124 Hackman & Hruschka (2013) have criticized our studies across USA states of the cultural variables homicide, child maltreatment, religiosity, and family ties. We published analyse...

We recently proposed a new model to explain cross-national variation in the frequency of intrastate conflict based on the parasite-stress theory of sociality. In regions of high pathogen severity, cultures are characterized by xenophobia and ethnocentrism, which function in the avoidance and management of infectious disease. The xenophobia expresse...

Throughout the world people differ in the magnitude with which they value strong family ties or heightened religiosity. We propose that this cross-cultural variation is a result of a contingent psychological adaptation that facilitates in-group assortative sociality in the face of high levels of parasite-stress while devaluing in-group assortative...

In the target article, we presented the hypothesis that parasite-stress variation was a causal factor in the variation of in-group assortative sociality, cross-nationally and across the United States, which we indexed with variables that measured different aspects of the strength of family ties and religiosity. We presented evidence supportive of o...

Researchers using the parasite-stress theory of human values have discovered many cross-cultural behavioural patterns that inform a range of scholarly disciplines. Here, we apply the theory to major categories of interpersonal violence, and the empirical findings are supportive. We hypothesize that the collectivism evoked by high parasite stress is...

In this study, we tested the parasite-stress hypothesis for the distribution of intelligence among the USA states: the hypothesis proposes that intelligence emerges from a developmental trade-off between maximizing brain vs. immune function. From this we predicted that among the USA states where infectious disease stress was high, average intellige...

Research over the past decade has documented clear, robust changes in women's sexual preferences and interests across the ovarian cycle. When fertile, women are particularly attracted to a number of masculine male features (e.g., masculine faces, voices, scents and bodies) and other traits, and especially when they evaluate men's “sexiness” rather...

A substantial body of work demonstrates that women's mate preferences change across the ovulatory cycle. When fertile in their cycles, women are especially attracted to masculine features (e.g., faces, voices, bodies), socially dominant behavior, and male scents associated with body symmetry and social dominance. Women may also find intelligent men...

We propose that consanguineous marriages arise adaptively in response to high parasite prevalence and function to maintain coadapted gene complexes and associated local adaptation that defend against local pathogens. Therefore, a greater prevalence of inbreeding by consanguineous marriage is expected in geographical regions that historically have h...

In this study, we hypothesize that the worldwide distribution of cognitive ability is determined in part by variation in the intensity of infectious diseases. From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks. Usi...

Certain loud calls made by female red junglefowl and Lapland longspurs are given most frequently immediately after egg laying, when a copulation should have the highest probability of fertilizing the next egg to be laid. In these species there is considerable male-male interaction for access to fertilizable females, and males are attracted to or fo...

Reproductive-effort theory predicts that parents of any given age should expend more parental effort (1) as their residual reproductive value declines, and (2) as the reproductive value of offspring increases. An observational and experimental study of nest defense by captive red jungle fowl hens was used to examine these two predictions. Both youn...

The parasite-stress model of human sociality proposes that humans' ontogenetic experiences with infectious diseases as well as their evolutionary historical interactions with these diseases exert causal influences on human psychology and social behavior. This model has been supported by cross-national relationships between parasite prevalence and h...

Geographic and cross-national variation in the frequency of intrastate armed conflict and civil war is a subject of great interest. Previous theory on this variation has focused on the influence on human behaviour of climate, resource competition, national wealth, and cultural characteristics. We present the parasite-stress model of intrastate conf...

Senescence arises from age-specific deterioration of the soma as a consequence of optimization of life history, and such effects of senescence should appear when comparing species that differ in intensity of sexual selection, as well as when comparing, within a species, the two sexes that often differ in intensity of sexual selection. However, any...

Despite the importance of extrapair copulation (EPC) in human evolution, almost nothing is known about the design features of EPC detection mechanisms. We tested for sex differences in EPC inference-making mechanisms in a sample of 203 young couples. Men made more accurate inferences (φmen = 0.66, φwomen = 0.46), and the ratio of positive errors to...

The countries of the world vary in their position along the autocracy–democracy continuum of values. Traditionally, scholars explain this variation as based on resource distribution and disparity among nations. We provide a different framework for understanding the autocracy–democracy dimension and related value dimensions, one that is complementar...

Why are religions far more numerous in the tropics compared with the temperate areas? We propose, as an answer, that more religions have emerged and are maintained in the tropics because, through localized coevolutionary races with hosts, infectious diseases select for three anticontagion behaviours: in-group assortative sociality; out-group avoida...

Over a dozen studies now report increases in women's preferences for various male traits at high fertility points in the menstrual cycle — namely, traits that, purportedly, were ancestral indicators of good genetic quality. Very few studies have examined the proximate mediators responsible for these preference shifts. The current study was designed...

Parasite–host coevolutionary races are spatially variable across species’ or human cultural ranges. Assortative sociality, biased toward local conspecifics, and limited dispersal (philopatry) in humans and other organisms can be adaptive through reduced contact with dangerous contagions harbored by distant/non-local conspecifics. These factors can...

Pathogenic diseases impose selection pressures on the social behaviour of host populations. In humans (Homo sapiens), many psychological phenomena appear to serve an antipathogen defence function. One broad implication is the existence of cross-cultural differences in human cognition and behaviour contingent upon the relative presence of pathogens...

For several decades, scholars of human sexuality have almost uniformly assumed that women evolutionarily lost oestrus--a phase of female sexuality occurring near ovulation and distinct from other phases of the ovarian cycle in terms of female sexual motivations and attractivity. In fact, we argue, this long-standing assumption is wrong. We review e...

SummaryA Darwinian adaptation is an organism's feature that was functionally designed by the process of evolution by selection acting in nature in the past. Functional design rules out explanations of drift, incidental effect, phylogenetic legacy and mutation. Elucidation of the functional design of an adaptation entails an implicit reconstruction...

Conservatives and liberals have markedly different ideologies. Conservatives, in comparison to liberals, are risk averse and prefer social inequality, traditionally established and familiar in-group values, and familial allegiance. Liberals are risk prone, are open to new views and ways, value equality and out-group relations, and exhibit high inde...

Preferences for mates that possess genes dissimilar to one's own at the major histocompatibility complex (MHC), a polymorphic group of loci associated with the immune system, have been found in mice, birds, fish, and humans. These preferences may help individuals choose genetically compatible mates and may adaptively function to prevent inbreeding...

Testosterone (T) appears to facilitate what biologists refer to as mating effort--the investment of time and energy into same-sex competition and mate-seeking behavior. Multiple studies show that men who are romantically involved (i.e., are paired) have lower T than single men, which may be due to a facultative adjustment by men of T levels in resp...

We investigated aspects of self-reported health history–the number and duration of respiratory and stomach or intestinal infections and the number of uses of antibiotics over the last 3 years–in relation to measured facial masculinity, developmental instability [facial asymmetry and body fluctuating asymmetry (FA)] and facial attractiveness in a sa...

In socially monogamous species in which males heavily invest in offspring, there arises an inevitable genetic conflict between partners over whether investing males become biological fathers of their partners' offspring. Humans are such a species. The ovulatory-shift hypothesis proposes that changes in women's mate preferences and sexual interests...

Recently, several studies have suggested that the biological literature may be biased because studies with particular effect sizes are more likely to get published. However, only one published direct test comparing effect sizes of a representative sample of published and unpublished studies exists in biology. We performed an additional direct test...

Normally ovulating women have been found to report greater sexual attraction to men other than their own partners when near ovulation relative to the luteal phase. One interpretation is that women possess adaptations to be attracted to men possessing (ancestral) markers of genetic fitness when near ovulation, which implies that women's interests sh...

As collaborators of Anders Pape Moller, we were shocked and surprised to read that he was accused of data fabrication (“Ecologists roiled by misconduct case,” G. Vogel, F. Proffitt, R. Stone, News of the Week, 30 Jan., p. [606][1]). We have never had cause to be concerned about any aspect of

The Mecoptera (scorpion flies) comprise c.500 extant species in 32 genera and 9 families. They are known from the Lower Permian and are of supposed ancestral relationship with the Diptera and Lepidoptera. Panorpidae and Boreidae are the dominant families in northern continents, Bittacidae in southern continents. Morphology, development and physiolo...

We studied fluctuating asymmetry (FA) in two generations of the bulb mite Rhizoglyphus robini. We used Procrustes analyses, which allow the comparison of dimensionless shapes of body sides. We found little (<4%) directional asymmetry in either sex. Of the two morphs occurring in this species, fighters, which possess a thickened third pair of legs,...

Previous research indicates that the scent of developmental stability (low fluctuating asymmetry, FA) is attractive to women who are fertile (at high-conception risk points in their menstrual cycles), but not to other women or men. Prior research also indicates that the scent of dissimilarity in major histocompatibility complex (MHC) genes may play...

Current theoretical and empirical findings suggest that mate preferences are mainly cued on visual, vocal and chemical cues that reveal health including developmental health. Beautiful and irresistible features have evolved numerous times in plants and animals due to sexual selection, and such preferences and beauty standards provide evidence for t...

In this paper we respond to two frequent criticisms of our book, A Natural History of Rape (Thornhill & Palmer, 2000). The first criticism portrays the book as little more than a "just-so story" that human rape is an adaptation. We demonstrate that this portrayal is not accurate. The second criticism reflects a common response to the book s challen...

Recently, women have been found to prefer the scent of symmetrical men and relatively masculine male faces more during the fertile (late follicular and ovulatory) phases of their menstrual cycles than during their infertile (e.g., luteal) phases. These findings make most theoretical sense if men's symmetry is associated with the masculinity of thei...

Current theoretical and empirical findings suggest that mate preferences are mainly cued on visual, vocal and chemical cues that reveal health including developmental health. Beautiful and irresistible features have evolved numerous times in plants and animals due to sexual selection, and such preferences and beauty standards provide evidence for t...

This paper treats the topics that have been of long interest to aestheticians. Traditional aesthetics, i.e., aesthetics in philosophy, is broad and diverse, including such topics as the beauty of ideas as well as the beauty of body form, natural landscapes, scents, ideas and so on. Some colleagues have suggested that I provide a succinct definition...

Do women have special-purpose evolved adaptation that functions in pursuing copulations with men other than the main romantic partner, just as they have specialized adaptation for seeing color, estimating object distance, digesting fat, responding to stress, and a multitude of other problems that gave rise to successful selection for functional tra...

The existence of additive genetic variance in developmental stability has important implications for our understanding of morphological variation. The heritability of individual fluctuating asymmetry and other measures of developmental stability have frequently been estimated from parent-offspring regressions, sib analyses, or from selection experi...

Because ancestral women could have obtained genetic benefits through extra-pair sex only near ovulation, but paid costs of extra-pair sex throughout the cycle, one might expect selection to have shaped female interest in partners, other than primary partners, to be greater near ovulation than during the luteal phase. Because men would have paid hea...

In many studies, fluctuating asymmetry (FA) has been used as a measure of individual differences in developmental imprecision. A model of how variation in developmental imprecision is associated with variation in asymmetry is described and applied to important issues about FA. If individual differences in developmental imprecision exist, asymmetry...

A single trait's fluctuating asymmetry (FA) is expected to be a poor measure of developmental instability. Hence, studies that examine associations between FA and outcomes expected to covary with developmental instability often have little power in detecting meaningful relationships. One way of increasing the power of detecting relationships betwee...

The notion that surface texture may provide important information about the geometry of visible surfaces has attracted considerable attention for a long time. The present study shows that skin texture plays a significant role in the judgment of female facial beauty. Following research in clinical dermatology, the authors developed a computer progra...

The notion that surface texture may provide important information about the geometry of visible surfaces has attracted considerable attention for a long time. The present study shows that skin texture plays a significant role in the judgment of female facial beauty. Following research in clinical dermatology, the authors developed a computer progra...

The ratio between the length of the 2nd and 4th digit (2D:4D) is sexually dimorphic, with mean male 2D:4D lower than mean female 2D:4D. It recently was suggested that 2D:4D is negatively correlated with prenatal testosterone and positively correlated with prenatal estrogen. It is argued that high prenatal testosterone and low estrogen (indicated by...

Testosterone, particularly prenatal testosterone, has been implicated in the aetiology of many extragenital sexually dimorphic traits. It is difficult to test directly for the effect of prenatal testosterone in humans. However, Manning, Scutt, Wilson, and Lewis-Jones (1998b) have recently shown that the ratio of the length of the 2nd and 4th digits...