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hedeemsuniversalandcrucial forhumanculture.Heclaimsthat animals behave like ‘psychopaths’ in that they show noremorse, empathy, anxiety, or guilt. This latter statementflies in the face of much modern primate biology, althoughthere are no doubt interesting differences that need to bemapped more carefully, rather than assumed. Sterelny, inthe last chapter, recognises ‘the complaint (by some contri-butors of this volume) that as soon as an apparently dis-tinctive human capacity is found not be distinctive after all,it ceases to count as a criterion of culture’. I concur, and see itas a positive sign, as cleverly designed experiments andimpressive longitudinal datasets seem to be constantlyrefining the mapping of these boundaries.

What remains to be done? Studying the interactionsbetween the three main sources of geographic variation inbehaviour (genetic predispositions, ecological conditionsand social transmission of innovations) in nature is apriority. Having established that observational forms ofsocial learning have a role in geographic variation in greatape behaviour, how dowe estimate its relative importance?Of all suggestions put forward in the book, two are mostpromising. First, a cultural approach requires that thebehavioural variants begin as rare innovations – anassumption that should now be tested with naıve animalsin captivity [7]. Second, correlations between pairs ofanimals (of the same or different populations) in theirrepertoires of behavioural variants can be used to revealthe relative importance of genetic similarity, ecologicaloverlap or social association. Future work on animal cul-ture would benefit from rigorously addressing ecologicaland genetic factors. That kind of data will be available soon

Corresponding author: Surridge, A.K. (aks59@cam.ac.uk).

for great apes and cetaceans, and will undoubtedly movethe debate forward.

On an ultimate level, culture can only have lastingevolutionary consequences if it leaves a genetic legacybehind, for instance, trait changes occurring potentiallyas a result of interactions of organisms with theirenvironment. The book does not cover these aspects ofcultural evolution at all, but perhaps the time is not yetripe. With the advent of new genomic tools, such as next-generation sequencing, decoupling variation in behaviourcaused by genetic selection and drift from that generatedthrough social learning might become a realistic targeton a much finer scale. With these exciting developmentsat hand, I hope that Laland and Galef can entitle theirnext collaborative effort ‘The Answers to Animal CultureQuestions’.

References1 Whiten, A. et al. (1999) Culture in chimpanzees. Nature 399, 682–6852 van Schaik, C.P. et al. (2003) Orangutan cultures and the evolution of

material culture. Science 299, 102–1053 Krutzen, M. et al. (2005) Cultural transmission of tool use in bottlenose

dolphins. Proc. Natl. Acad. Sci. U. S. A. 102, 8939–89434 Laland, K.N. and Janik, V.M. (2006) The animal cultures debate.Trends

Ecol. Evol. 21, 542–5475 Krutzen, M. et al. (2007) The animal cultures debate: response to Laland

and Janik. Trends Ecol. Evol. 22, 6–166 Fragaszy, D.M. and Perry, S., eds (2003) The Biology of Traditions.

Models and Evidence, Cambridge University Press, (Cambridge, UK)7 van Schaik, C.P. et al. (2006) Innovation in wild Bornean orangutans

(Pongo pygmaeus wurmbii). Behaviour 143, 839–876

0169-5347/$ – see front matter � 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.tree.2009.06.004 Available online 10 August 2009

Book Review

Snaking through primate evolutionThe Fruit, the Tree, and the Serpent: Why We See So Well by Lynne A. Isbell. Harvard University Press, 2009.US$45.00/£33.95 hbk (224 pages) ISBN 13: 978 0 674 03301 6

Alison K. Surridge

Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK

Adaptations that have occurred through-out the course of primate evolution and

the influence of snakes on primate evolution in general andprimate visual adaptations in particular.

those that are ultimately thought to ‘makeus human’ hold a fascination for many.Tool use, language, large brain size andenhanced visual acuity are among suchtraits that are studied extensively byanthropologists, but it is the latter thatis the focus of The Fruit, the Tree, and theSerpent. The author’s research interests

in social dispersal led her to the discovery that Asian

primates have a retrovirus closely related to that carriedby the venomous Russell’s viper [1], indicating a sharedantagonistic history. So began a ten-year investigation into

For many people, snakes evoke irrational feelings offear, despite having no previous negative experiences.Among primates, humans are not unique in this response.Winding its way through the central thesis ofThe Fruit, theTree, and the Serpent is the ‘snake detection theory,’ whichargues that our morbid fascination with snakes and theirprominence in religion and folklore is a consequence of along evolutionary history of predation. It is an interestingconcept that a fear of snakes and an ability to react rapidlyto them was hard-wired into our neural circuitry early inprimate evolution. Isbell argues that selection by snakes aspredators lead to a large number of neural and visualadaptations and (rather tenuously) might even have ledto the origins of pointing and language. The theory is a

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contentious one, but this book aims to illuminate evidencein its favour from a wide range of scientific disciplines.

One startswith an overviewof primate biogeographyandadaptation.Reachingandgrasping, orbital convergenceandforward-facing eyes separate primates fromothermammalsand the various existing theories to explain these traits arecovered concisely. The chapter on primate vision aims toexplain complex neurophysiology in simple terms, which isimportant because it enables the nonspecialist reader tomake up their ownmind regarding the evidence in favour ofthe snake detection theory. The mechanism by which thevisual system is involved in the recognition of fear in thefaces of conspecifics is mentioned in passing. Given theimportance of social interactions in primate evolution andprimate brain expansion, I would have liked to see moreinformation provided on the parts of the visual pathwayandprocessing networks that are involved in facial recognitionanddetectionof emotions in conspecifics.Thismightprovidean alternative explanation for why certain systems haveevolved in complexity. The author goes on to discuss theorigin ofmodernpredators andwhy snakes in particular areimportant. She also explains by what means the visualsystem links to fear, the ways in which anthropoid primateevolution was modified beyond that of more ‘primitive’primates by exposure to venomous snakes and why onlyprimates have evolved these adaptations in response tosnake predation. The final chapters cover ways in whichthe snake detection theory might be tested and its implica-tions for human evolution.

There are problems that can be found in the reasoningthroughout this book, if the reader chooses to look for them.For example, it is mentioned several times that enhancedvision comes at a cost to olfaction (i.e. there is a trade-off).This is used as evidence for why only primates have

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increased their visual acuity in response to snakes: theirdiet of fruit and flowers ‘permitted’ the loss of olfaction,which was presumably too costly for other mammals to dowithout. For me, it is difficult to reconcile the idea that onesense must be lost for another one to be gained. It might bethat olfactory systemsdeclinedaftervision improved simplybecause they were not needed anymore (see [2]). However,The Fruit, the Tree, and the Serpent also highlights fascinat-ing areas of research which are waiting to be studied in anevolutionary framework. Patterns that inadvertentlysimulate snakeskin characteristics can stimulate relevantneurons (e.g. Ref. [3]), which might have evolved for rapidsnakedetection.This ideahasyet tobe investigateddirectly.

The snake detection theory is largely untested and thereare inevitably a lot of ‘ifs’ and ‘buts’ required to make theinformation presented in The Fruit, the Tree, and theSerpent fit the theory. Even so, I would recommend thisbook to anyone with a general interest in primate evol-ution. Sections will be controversial to experts in certainfields and the author acknowledges that her book is likelyto rankle some. However, I found the book to be an enjoy-able read with broad scope and simple explanations. Isbellshould be commended for moving the field forward and forinspiring the testing of new hypotheses.

References1 Anderson, P.R. et al. (1979) Evolutionary relatedness of viper and

primate endogenous viruses. Science 204, 318–3212 Gilad, Y. et al. (2004) Loss of olfactory receptor genes coincides with the

acquisition of full trichromatic vision in primates. PloS Biol. 2, 120–1253 Okusa, T. et al. (2000) Cortical activity related to cue-invariant shape

perception in humans. Neuroscience 98, 615–624

0169-5347/$ – see front matter � 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.tree.2009.07.001 Available online 27 August 2009