Content uploaded by Graham Budd
Author content
All content in this area was uploaded by Graham Budd on Apr 20, 2018
Content may be subject to copyright.
[16:54 27/9/2013 Sysbio-syt042.tex] Page: 915 913–918
2013 BOOK REVIEWS 915
Stelbrink B., Albrecht C., Hall R., von Rintelen T. 2012. The
biogeography of Sulawesi revisited: is there evidence for a vicariant
origin of taxa on Wallace’s “anomalous island”? Evolution 66:
2252–2271.
VanWelzen P.C., Parnell J.A.N., Slik J.W.F. 2011. Wallace’s line and plant
distributions: two or three phytogeographical areas and where to
group Java? Biol. J. Linn. Soc. 103:531–545.
Van Welzen P.C., Raes N. 2011. The floristic position of Java. Gardens’
Bulletin Singapore 63:335–345.
Wallace A.R. 1880. Island life, or the phenomena and causes of insular
faunas and floras, including a revision and attempted solution of
the problem of geological climates. London: Macmillan.
Williams D.M., Ebach M.C. 2006. The data matrix. Geodiversitas
28:409–420.
Woodruff D.S. 2010. Biogeography and conservation in Southeast
Asia: how 2.7 million years of repeated environmental fluctuations
affect today’s patterns and future of the remaining refugial–phase
biodiversity. Biodiver. Conserv. 19:919–941.
Visotheary Ung, Centre de Recherche en Paléobiodiversité et
Paléoenvironnements (UMR 7207: CNRS MNHN UPMC), 57 rue Cuvier
CP 48, 75005 Paris, France; E-mail: visotheary.riviere-ung@snv.jussieu.fr
Syst. Biol. 62(6):915–917, 2013
© The Author(s) 2013. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved.
For Permissions, please email: journals.permissions@oup.com
DOI:10.1093/sysbio/syt043
Advance Access publication June 20, 2013
The Cambrian Explosion: The Reconstruction
of Animal Biodiversity. By Douglas H. Erwin and
James W. Valentine. 2013. Greenwood Village, CO,
Roberts & Co., x+406 pp. ISBN 978-1-936221-03-5, $US60
(hardback).
Everything about the Cambrian Explosion sounds
exciting: it is the Big Bang of evolution, if you like. Along
with the extinction of the dinosaurs at the Cretaceous–
Paleogene boundary, some 66 Ma, it is the evolutionary
event that sticks in everyone’s mind, when all of the
animals apparently appeared in a well, explosion, over
500 Ma. Given this fame, or even notoriety, it is rather
surprising how poorly the topic is served by book-length
treatments.
Of course, there are books about it, but many of these
turn out to be about particular aspects of the subject
rather than attempting a comprehensive treatment.
Given that a “comprehensive treatment” needs
minimally to span the topics of fossil preservation and
interpretation, oceanic and atmospheric geochemistry,
animal systematics and development, not to mention
ecological theory, sedimentology, and radiometric and
stable isotopic dating (along with a slew of others)
perhaps this is not very surprising. Anyone who sits
down and attempts such a thing must sooner or later be
faced with a feeling of helplessness. That the thing can
be done at all is thus a thing of wonder. That two of the
most experienced and interesting commentators on the
topic have done so is a cause for some celebration, then.
Having said that, one must at once admit, as the
authors themselves cheerfully do in their introduction,
that this volume is not all things to all people. It was
written at the request of Nicole King, so that her graduate
students could have a useful reference guide to the
Cambrian explosion—a role that this volume eminently
fills. It is sturdily constructed, beautifully illustrated,
and does indeed make a fair stab at covering most
of the major issues. After the introductory material,
successive chapters cover the geological context of
the Cambrian explosion, including stratigraphy and
correlation; and approaches to reconstruction of the
late Precambrian–Cambrian world (a transition that
took place around 635–500 Ma). The next chapter
covers an introduction to animal classification, including
molecular phylogenies, and then plunges into a primer
of animal morphology, starting with the likely sister
group to the animals, the choanoflagellates, and ending
with lophotrochozoans. The authors then turn their
attention, in a particularly well-illustrated chapter, to
the enigmatic “Ediacara”-style biota that existed from
about 579 Ma to around the beginning of the Cambrian.
This leads naturally into a very substantial chapter
covering the Cambrian faunas, including some excellent,
if on occasion somewhat disturbing, reconstructions of
Cambrian animals. Perhaps, we can be grateful that the
recent description of Spartobranchus tenuis (Caron et al.
2013) came just too late for inclusion in the book. The
authors also struggle here with the problematic nature
of many Cambrian organisms, taking deuterostomes,
lophotrochozoans, and arthropods as their examples. In
a short closing summary, they then attempt to present
what they think the data mean in terms of diversity,
which is relatively straightforward, and disparity, which
is not.
The following section deals with the evolutionary
processes that might lie behind these patterns. First up
come the ecological patterns of change, where the topic
of “ecosystem engineering” features prominently, and
then an informed discussion of the genetic basis for
body plan development and its possible involvement
in body plan evolution. Finally, in a relatively brief
section of the book, the authors sum up their views on
the missing “ghosts”—organisms that we know must
have been present at some time but that have left no
trace—and the implications this has for the integration
of the data they discuss in the book, especially that from
developmental sources. A substantial appendix records
first evolutionary appearances of phyla and classes.
Such is a (very brief) outline of the contents. How
should it be judged? First some quibbles. Like many
first editions, it suffers from its (inevitable) fair share of
slips—for example, veterans of the Cambrian literature
on the hunt for misspellings of Stefan Bengtson’s
name will not be disappointed. The specimen of
Cloudina illustrated is not from Namibia but China;
Downloaded from https://academic.oup.com/sysbio/article-abstract/62/6/915/1709635
by guest
on 20 April 2018
[16:54 27/9/2013 Sysbio-syt042.tex] Page: 916 913–918
916 SYSTEMATIC BIOLOGY VOL. 62
and some of the small shelly fossil assignments are
somewhat surprising—for example, a figure caption
claims that what I think is probably Mobergella is a
“stem bivalve,” which is certain to raise some eyebrows.
The summary “best guess” phylogeny on page 75 is
peculiar—apart from (I assume) inadvertently placing
the protostome–deuterostome boundary in the wrong
place (between echinoderms and hemichordates!), it also
has some rather strange sister-group relationships, such
as between brachiopods and rhabditophorans. In any
case, it is flatly contradicted in many places by the
microRNA tree on the very next page.
As well as presenting the basic evidence for the
Cambrian explosion, the authors also have a thesis
to defend. This is that the fossil record of the early
Cambrian shows a marked clumping of taxa—and they
point out how dissimilar the fossil record is compared
with known ecological radiations, such as that of, for
example, cichlid fish (a pattern that was pointed out as
long ago as 1850 by Adam Sedgwick, incidentally). As
a result, they consider that to think of the Cambrian
explosion as an adaptive radiation is to stretch the term
to its breaking point. As a general rule, this may or
may not be true—trilobites, the most iconic and diverse
of all Cambrian fossils, hardly seem to follow it (Foote
1990;Budd 2013). However, assuming it is true, what
are we to make of it? Can we take it, as the authors
shyly hint, that the underlying pattern—now lost to
us—was also different from adaptive radiation? The
authors quite rightly reject any notion of “saltational”
leaps in evolutionary organization. However, at the same
time, they want to attribute the large gaps between
the known organisms—their disparity—to a particular
type of evolutionary mechanism related to how the
developmental genome is organized. I have to say that
I find this claim to be problematic, particularly as the
authors themselves (p. 72) seem elsewhere to admit
to these gaps resulting from a failure of the fossil
record to preserve the intermediates that must have
existed. If such intermediates existed but have not been
preserved, then in what sense is the developmental
genome controlling and restricting the known clumped
pattern of morphologies (or rather, how could we know
how to partition the effect between the genome and
preservational vagaries)?
The problems with such a view can be seen in other
ways as well. The authors want to loosely correlate levels
of change within the developmental genome with the
Linnean hierarchy. Valentine has published more clearly
than anyone else that, although both are hierarchies,
they are very differently structured, and thus one cannot
simply map one on to the other. What I would like
to see is not the usual lineup of “phyla-classes-orders”
with “kernels-gene batteries,” etc. but, rather, a mapping
of the attainment of developmental mechanisms onto
a phylogenetic tree of the phyla. As soon as you try
to do this, the problems of asserting a hierarchical
developmental control of evolutionary morphological
conservation become apparent—the phyla simply do
not appear on the tree in the right way in order
for this to make sense. In other words, it seems to
me that the approach taken in the book—it is by
no means necessarily an invalid one, incidentally—
is developmentally an “extantist” one—by making
the assumption that the developmental maintenance
of today’s organs and systems is the same as their
developmental origin. But if we are to gain any insights
from the field of “evo-devo” today, surely one must
be that development must itself have evolved—a point,
however, that is curiously resisted by many of its
practitioners.
One of the good things about the book is the insistence
on the importance of all aspects of development,
phylogeny, ecology, and environment in coming to a
mature understanding of the Cambrian Explosion—in
contrast to some previous efforts at “explaining” it that
can, I think, remain nameless. There is, for them, no
magic bullet that is the ultimate fix for this problematic
event. In perhaps the most interesting part of the book,
the authors grapple with the problems of ecosystem
engineering and niche construction—the complex
feedbacks between organisms and environments that
enable and shape radiations. It is an eerie thought, of
the first mobile bilaterians appearing at one place in the
world, and spreading across it, creating epoch-making
change in their wake and adapting on the way. But did
they arrive at the far ends of the earth in the same
shape as they left its departure point or had they already
massively diversified into the virgin territories they
encountered—telegraph, or Chinese whispers, if you
like? Such timing differences might have had significant
effects on all subsequent evolution, as in the former case
diversification would be into ecospace that was in some
sense already occupied, and in the latter without such
constraint.
One of the frustrating things about the Cambrian
Explosion, which the authors (perhaps understandably,
given their target audience) politely do not fully bring
out, is how poorly constrained the critical time period
still is. As a result, it is simply impossible at the current
time to get answers to apparently sensible questions
like “where did the first burrowing trace fossils appear?
Which trilobite genus is the oldest?” and so on. Yet, if
we really want to understand the delicate interactions
between environment and evolution that may stand
behind all subsequent events, it might well be that it is
exactly this detail that we need—and this is some way off.
In other words, although we can see the spectacular
painted backdrop against which the Cambrian
Explosion is played out—the Neoproterozoic
glaciations, the continental collisions and break-up,
and the wild fluctuations in geochemistry throughout
the period—it remains difficult to see how these relate
in any detailed and interesting way to evolutionary
innovations at the base of the bilaterian animals and
before. (Unlike the authors, I find it hard to image the
sponges arising almost 200 myr before the base of the
Cambrian.) Erwin and Valentine quite sensibly do not
offer any glib answers here, but their compilation and
enlightened discussion of much of the relevant data in
Downloaded from https://academic.oup.com/sysbio/article-abstract/62/6/915/1709635
by guest
on 20 April 2018
[16:54 27/9/2013 Sysbio-syt042.tex] Page: 917 913–918
2013 BOOK REVIEWS 917
one volume will surely open windows for their readers
into the depth and complexity of what they rightly
describe as the “once-in-an-era happening” that is the
Cambrian Explosion.
Erwin and Valentine’s book is a good introduction to
the topic they address, and perhaps the best available.
This is not exactly a book for specialists—and the authors
themselves admit to this. It does not, for example, really
dig into (in particular) the geological data to show
where all of the uncertainties lie, but presents a more
or less optimistic “consensus” view of where we are at
the moment. This geological part has been consciously
written to be accessible to all biologists, and in this it
succeeds, although one might think that some accuracy
has been sacrificed as a result. Conversely, the sections
on gene regulation are quite detailed and would be hard
to follow without a certain amount of background—
again, suitable for readers coming from a biological
background. Readers of Systematic Biology might also
note that, despite the fairly constant references to
phylogeny, the book could have been sharpened by
more rigorous attention to what phylogenies actually
tell us.
REFERENCES
Budd G.E. 2013. At the origin of animals: the revolutionary Cambrian
fossil record. Curr. Genomics 14 (in press).
Caron J.-B., Conway Morris S., Cameron C.B. 2013. Tubiculous
enteropneusts from the Cambrian period. Nature 495:503–506.
Foote M. 1990. Nearest-neighbor analysis of trilobite morphospace.
Syst. Zool. 39:371–382.
Graham E. Budd, Department of Earth Sciences, Palaeobiology,
Uppsala University, Villavägen 16, Uppsala SE-75236, Sweden;
E-mail: graham.budd@pal.uu.se
Syst. Biol. 62(6):917–918, 2013
© The Author(s) 2013. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved.
For Permissions, please email: journals.permissions@oup.com
DOI:10.1093/sysbio/syt046
Advance Access publication July 22, 2013
Phylogenomics: A Primer. By Rob DeSalle and
Jeffrey A. Rosenfeld. New York: Garland Science. 2013.
xiv+338 pp. ISBN 978-0-8153-4211-3, $79 £38 (paperback).
Phylogenomics as a separate field was named 15
years ago (Eisen 1998) and appears to be growing
exponentially, judging from the number of publication
titles containing the term: 27 between 2000 and 2005,
89 between 2006 and 2010, and 76 from 2010 to the
middle of 2013 (Web of Science search on 5 July 2013).
Phylogenomics covers the intersection of molecular
biology and evolution, or perhaps more precisely,
phylogenetics and genomics (Eisen and Fraser 2003).
We are aware of only one other attempt at a textbook
prior to Phylogenomics: A Primer, namely the collection
of protocols and resources compiled by Murphy (2008).
The primer now offered by Rob DeSalle and Jeffrey
Rosenfeld is timely and probably eagerly awaited by
many professors under pressure to offer courses in
phylogenomics. This, at least, was our case.
The book is, according to the authors, intended
for “advanced undergraduate students and graduate
students in molecular biology, comparative biology,
evolution, genomics, biodiversity, and informatics.”
These students may enjoy the easy writing style, and
with guidance they will benefit from parts of this primer.
However, this is not the introduction to the research
questions, approaches, and tools of phylogenomics we
were hoping for. There is too much phylogenetics and
too little genomics.
The first chapter of Phylogenomics starts with a
description of the increasing role of bioinformatics in
the analysis of DNA data, a half page on microarrays
(followed by a long table on microarray data that has no
apparent connection to anything), a paragraph on the
human genome project, and sections on non-parametric
statistical analyses, maximum-likelihood analyses, and
Bayesian analyses. All of this is without citations or
references to later sections of the book, where these
topics are taken up in more depth. Here and throughout,
there is frequent name-dropping without any indication
about why a person’s work is brought up, when it
was done, or how it relates to phylogenomics. Typical
examples are: “This is the basis of science; as Immanuel
Kant stated, ‘Science is organized knowledge’” (p. 11;
this appears to be a confusion with the philosopher
Ernst Cassirer); “Recently the entire genomes of Dr Craig
Venter and Dr James Watson have been sequenced by
using only a fraction of the time and cost expended
in the initial human genome projects” (p. 24; there is
nothing before or after this sentence about these doctors);
and “Interestingly, Charles Darwin and Gregor Mendel
lived around the same time, and if communication at
the time had been more extensive, then each would have
known about the other’s theories and a quicker synthesis
of genetics and evolution might have occurred” (p. 36).
Actually, communication in Old Europe was not what
held things back. Mendel studied The Origin of Species
in a German translation of 1863, and in his personal
copy he made many notes in the margin. Conversely,
Darwin had several opportunities to read Mendel or
Mendel’s results, but seems to have shied away from the
mathematical annotations (Galton 2009). We doubt that
students will benefit from such haphazard strewing in
of the history of biology, especially without mention of
years or even relevant centuries.
Chapter 2 covers the structure of DNA, the codon
code, protein folding, next-generation sequencing, and
microarrays, all in a cursory manner. Chapter 3 covers
microevolution, macroevolution, species concepts, and
Downloaded from https://academic.oup.com/sysbio/article-abstract/62/6/915/1709635
by guest
on 20 April 2018
