Evolutionary psychology an introduction 3rd ed 2014

1.2 The application of evolutionary thinking in four disciplines 171.3 Sociobiology, evolutionary psychology and political correctness 21 2.2 Mendel’s original laws of genetics using mod

THIRD EDITION

Written for undergraduate psychology students, and assuming little knowledge

of evolutionary science, the third edition of this classic textbook provides anessential introduction to evolutionary psychology Fully updated with the latestresearch and new learning features, it provides a thought-provoking overview ofevolution and illuminates the evolutionary foundation of many of the broadertopics taught in psychology departments The text retains its balanced andcritical evaluation of hypotheses and full coverage of the fundamental topicsrequired for undergraduates This new edition includes more material on thesocial and reproductive behaviour of non-human primates, morality, cogni-tion, development and culture as well as new photos, illustrations, text boxesand thought questions to support student learning Nearly 300 online multiplechoice questions complete the student questioning package This new materialcomplements the classic features of this text, which include suggestions for fur-ther reading, chapter summaries, a glossary and two-colour figures throughout

Lance Workmanis Honorary Visiting Professor of Psychology at the University

of South Wales

Will Readeris a Senior Lecturer in Psychology at Sheffield Hallam University

Evolutionary Psychology

An Introduction

THIRD EDITION

LANCE WORKMAN AND WILL READERUniversity of South Wales and Sheffield Hallam University

University Printing House, Cambridge CB2 8BS, United Kingdom

Published in the United States of America by Cambridge University Press, New York

Cambridge University Press is part of the University of Cambridge.

It furthers the University’s mission by disseminating knowledge in the pursuit of

education, learning and research at the highest international levels of excellence.

www.cambridge.org

Information on this title: www.cambridge.org/9781107622739

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 Lance Workman and Will Reader 2014

This publication is in copyright Subject to statutory exception

and to the provisions of relevant collective licensing agreements,

no reproduction of any part may take place without the written

permission of Cambridge University Press.

First published 2004

Second edition 2008

Third edition 2014

Printed in Spain by Grafos SA, Arte sobre papel

A catalogue record for this publication is available from the British Library

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Cambridge University Press has no responsibility for the persistence or accuracy of

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accurate or appropriate.

To Anna and Georgia Thank you for all the love you give I love you both.

List of boxes pageviii

7 The evolutionary psychology of social behaviour – kin relationships and conflict 198

8 The evolutionary psychology of social behaviour – reciprocity and group behaviour 222

1.2 The application of evolutionary thinking in four disciplines 171.3 Sociobiology, evolutionary psychology and political correctness 21

2.2 Mendel’s original laws of genetics (using modern terminology) 412.3 The evolution of our species – from ape to early archaic Homo sapiens 452.4 The Human Genome Project – unravelling the code to build a person? 492.5 The evolution of our species – the emergence of modern Homo sapiens 53

3.2 Fisher versus Hamilton–Zuk – attractiveness versus good genes 72

4.1 Bipedalism and pair-bonding part 1 – the provisioning hypothesis 984.2 Bipedalism and pair-bonding part 2 – why do men help out? 101

6.3 Behavioural genetics and the effects of the genes on the environment 177

7.4 The Cinderella Effect – the downside to parental investment? 212

8.4 Criticisms of Edward Wilson’s views on xenophobia 2418.5 A real prisoner’s dilemma – Philip Zimbardo’s prison experiment 245

11.3 Similarities between ourselves and other primates in facial expressions

provide clues about the origins of human facial expressions 337

11.5 Criticisms of the universality of emotions – human pigs and false smiles 346

12.3 Obsessive–compulsive disorder – an overactive verification module? 36912.4 Do women drive other women into a state of anorexia nervosa? 377

(Box 2.3) Human evolution

2.3 DNA

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(Box 2.5) Skeleton of a Homo erectus boy

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3.1 A family of elephant seals

By kind permission of Friends of the Elephant Seal, San Simeon, California 683.2 Harem size in relation to male

3.3 Male barn swallow

3.5 Widowbird average number of nests compared to tail length

(Box 3.5) Reconstruction of Neanderthal male

4.1 Primate evolutionary tree 904.2 Male chimpanzees often collaborate in hunting

4.5 Number of sexual partners desired

5.2 Apparatus used by Baillargeon (1987)

From Ren´ee Baillargeon, ‘Object permanence in 3½- and 4½-month-old

infants’, Developmental Psychology 23(5) (1987), 655–64

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1987 American Psychological Association Reproduced with permission 1325.3 Data from Baillargeon (1987)

From Ren´ee Baillargeon, ‘Object permanence in 3½- and 4½-month-old

infants’, Developmental Psychology 23(5) (1987), 655–64

5.6 How infants scan the human face

5.8 Simon Baron-Cohen’s conceptualisation of different brain types

Reprinted from Simon Baron-Cohen, ‘The extreme male brain theory of

autism’, Trends in Cognitive Sciences 6(6) (2002), 248–54.

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(Box 6.2) Kittens playing

(Box 6.5) Moral dilemmas used by Hauser et al (2007)

Reprinted from M D Hauser, F Cushman, L Young, K Kang-Xing and J

Mikhail, ‘A disassociation between moral judgements and justifications’,

Mind & Language 22(1) (2007), 1–21

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2007, with permission from Blackwell Publishing and the authors 192

(Box 7.3) Amaurobius fenestralis

7.3 Trivers’s model of parent–offspring conflict

8.3 Yanomam ¨o warriors

Photo by Napoleon A Chagnon, reproduced by kind permission 231

8.5 Example of an allocation matrix from Tajfel’s experiment 2439.1 Babbage’s Analytical Engine, 1834–71

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9.3 Shadow illusion by Edward Adelson

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9.4 Sir Frederick Bartlett

By Walter StonemanC National Portrait Gallery, London 2599.5 Amos Tversky and Daniel Kahneman

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(Box 10.3) The different stages of development for a number of hominins

From John L Locke and Barry Bogin, ‘Life history and language: Selection in

development’, Behavioral and Brain Sciences 29(3) (2006), 301–311

10.5 Ratio of neocortex to group size in non-human primate communities

(Box 11.3) A Chimpanzee smiling

(Box 11.3) B Facial signals in primates

11.1 The orbitofrontal cortex and the limbic system of the human brain 339

(Box 11.6) Nesse’s evolutionary tree of emotions

Reprinted from R M Nesse, ‘Natural Selection and the Elusiveness of

Happiness’, Philosophical Transactions of the Royal Society of London Series

13.1 Hans J ¨urgen Eysenck and Michael William Eysenck

(Box 13.3) Receptivity to evolutionary theory by year and birth order

Reprinted from Frank J Sulloway, ‘Birth order and evolutionary psychology:

a meta-analytic overview’, Psychological Inquiry 6(1) (1995), 75–80

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1995, by permission of Taylor & Francis Ltd, www.tandf.co.uk/journals 42213.3 Cristiano Ronaldo

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13.4 Primitive African bushman teaching a child how to track prey

14.2 The antimicrobial properties of different spices and herbs 446

14.4 A schematic diagram of the causal factors that led to the development of

advanced civilisation

(Box 2.1) Mendel’s demonstration of colour dominance in pea plants page40

4.2 Human mean mate preference scores in 9,474 people from 37 different

6.4 A proposed list of five moral ‘domains’ taken from Haidt and Joseph (2004)

Reprinted from Jonathan Haidt and Craig Joseph, ‘Intuitive ethics: how

innately prepared intuitions generate culturally variable virtues’, Daedalus

133(4) (2004), 55–66.C 2004, American Academy of Arts, with permission

7.1 Documented acts of apparent altruism in the animal kingdom 2008.1 Documented acts of apparent reciprocity between non-relatives in the animal

9.2 Percentage of choices in the abstract version of the Wason selection task 2789.3 Summary of results from abstract, cheat detection and altruist detection

10.1 Proportion of languages adopting each of the six logically possible word

10.2 The performance of English and Italian sufferers from SLI and controls on a

(Box 10.3) The different stages in human development according to Locke and

10.4 Sanskrit compared to other Indo-European languages ancient and

12.2 Changes to the classification of schizophrenia under DSM-5 381

13.1 The Big Five personality factors with typical characteristics of high and low

13.2 Summary of the different accounts of individual variation depending on theirsource (heritable versus environmental), and its effect (adaptive,

(Box 13.3) Partial correlations of the Big Five personality factors with birth order 42314.1 The peak ages at which individuals from a variety of disciplines were at their

Evolutionary psychology: past, present and future

If we use the 1992 publication date of The Adapted Mind as the birth date of

evolu-tionary psychology then, at the time of writing, it is now 21 years old, traditionallythe age at which children become adults and are expected to make their way inthe big, wide world It therefore seems to be an appropriate time to ask whetherevolutionary psychology has, as it were, become a respectable member of the scien-tific community, or whether it is still metaphorically tied to the apron strings of itsprogenitors at the University of California, Santa Barbara: loved by its parents butignored or even despised by its peers?

Part of an answer to this question can be seen in some subtle changes to this bookcompared to previous editions When we wrote the first edition way back in the late1990s and early 2000s the Santa Barbara version of evolution psychology was pre-

eminent The manifesto that was enshrined in The Adapted Mind proposed domain

specific mental modules that evolved in some mythical time and place referred to asthe Environment of Evolutionary Adaptedness, or the EEA We were enthralled bytales of hunter-gatherers in the Upper Pleistocene, of images of minds festooned withtools like Swiss Army knives, and of the principle that minds adapted for ancestraltasks might be less than successful in the twentieth (as it then was) century Thisprecocious child gained many vocal supporters in the scientific community, philoso-pher Daniel Dennett and psycholinguist Steven Pinker to name just two prominentmembers But there were many critics and many points of criticism DevelopmentalistAnnette Karmiloff-Smith, for example, questioned the notion of innate mental mod-ules, evolutionary anthropologists such as Eric Alden Smith pointed at problems withthe concept of the EEA and David Buller, well, David Buller seemed to dislike all of it.Not to be outdone by his erstwhile colleague, philosopher Jerry Fodor – who startedthe whole modularity movement in the first place – wrote a book with MassimoPiattelli-Palmarini which attempted to show that the whole concept of evolution bynatural selection was philosophically untenable (an argument that was dismantled

by two other philosophers, Ned Block and Philip Kitcher, who managed to keep theirfaces admirably straight throughout)

This third edition sees a subtle change in emphasis Rather than presenting theSanta Barbara school as the definitive version of evolutionary psychology, we discussother versions – some more influenced by behavioural ecology – that make noappeal to modularity, domain specificity and the EEA This should not be seen as us

xviii Preface to the third edition

distancing ourselves from the Santa Barbara school, but more our recognising whatthe core principles of an evolutionary psychology are and pointing out that a version

of evolutionary psychology can survive even if the aforementioned assumptions areproved to be incorrect As the philosopher of science Imre Lakatos might say, theseassumptions are part of the protective belt rather than the hard core of evolutionarypsychology These changes appear in many chapters, but particularlychapter 1

As well as these scientific and philosophical objections there are those who seeevolutionary psychology to be politically distasteful, particularly the research on sexdifferences in mate choice which is seen as merely reinforcing patriarchal stereotypes

of men and women Such a point seems to imply that evolutionary psychology issome kind of political dogma which provides us with rules as to how we should liverather than a field of scientific enquiry We hope we have addressed this issue inrevisions tochapter 1

Some adopters of our text have requested more primate comparative material inorder to help illuminate our understanding of the evolution of human reproductivestrategies In chapter 4 (mate choice) we have greatly expanded our coverage ofthe social and reproductive behaviour of primates by incorporating new material

on gorillas, bonobos and baboons In particular we feel that the discussion of femalecoalitional behaviour adds balance to the male-centred common chimpanzee materialpresented in earlier editions

Chapter 6on social development includes more recent research on the fascinatingnotion that children base their future reproductive strategy on the environment inwhich they develop, a hypothesis that gives the lie to those who think that evolu-tionary psychology is nothing more than a blind and mechanical unfurling of a rigiddevelopmental manifesto Evolution has not only made us sensitive to environmentalconditions, but it may also have given us a plan to help us deal with it

If proof were needed that the Santa Barbara school is alive and kicking chapter

9on cognition presents research that our memories might be sensitive to something

called s-value, or survival value Items that are presented under a context relevant

to conditions in the EEA seem to be more memorable than those presented in a EEA relevant context, even when the latter context is more familiar to participantsthan the former The fact that these results have been replicated by a team led bylong-standing memory researcher Henry Roediger III, who has no evolutionary axe

non-to grind, make these somewhat startling results all the more compelling Later in thechapter research by Tooby and Cosmides on deontic problem solving reinvigoratesthe notion of cheater detection as a means for understanding why some problems aredifficult and others easy A proposition that had previously been given something of

a pummelling by some of the big names in logical reasoning research

The ‘social chapters’ (7 and 8) both have new material that reflects current areas

of debate Chapter 7 now considers the ‘Cinderella Effect’ (the notion that parentsinvest more in ‘biological’ than in ‘non-biological’ offspring), while chapter 8 has

added a new pre-industrial culture – the Ach´e to add balance to debates concerninghow levels of reciprocation vary between different human societies The changes

to chapter 9 on language are rather more modest Here we include more on theapparent ability of prairie dogs to generate novel, mutually comprehensible ‘words’for things they have never encountered before, a re-evaluation of Chomsky and more

on FOXP2 and Specific Language Impairment We have included some new material

on the evolution of schizophrenia in chapter 12 alongside a recent evolutionarybased explanation for the eating disorder anorexia nervosa We anticipate that theseexplanations will appeal and disturb in equal measure

Chapter 13contains new material on the hunt for ‘candidate genes’ that are sidered to play a role in individual differences We are less positive about the findingshere than we were in previous editions, since these proposed single gene effects havenot stood up well to scrutiny or where they appear to do so the amount of variationthey account for between people appears to be really quite small Finallychapter 14

con-on culture re-evaluates the status of memes in cultural transmissicon-on and has a newsection on the importance of cultural specialisation to our rapid cultural develop-ment In many ways it is the topic of culture which sees evolutionary psychology

at its most inter-disciplinary, with contributions from historians, anthropologists,economists, biologists and philosophers as well as psychologists, and at its mostambitious: the attempt is to use evolution to partially explain how we got where weare now as twenty-first century hominins, the ape that tweeted, we might say

So where are we now? The above should make it clear that to us evolutionarypsychology is not an only child The offspring of Santa Barbara is still doing welland if it is not universally loved, well that is a result of its reluctance to adhere

to the status quo But its siblings (or half-siblings) that are perhaps not so strident

in their pronouncements, not so fundamentalist in their commitment to particularassumptions such as modularity or the EEA, are finding a voice too

Who should read this book?

We have designed this book for those with a background in psychology Unlike manybooks on the same topic we do not require readers to have prior knowledge of theintricacies of natural selection, genetics or inclusive fitness theory We have also tried

to relate evolutionary theory, where relevant, to some of the classic studies and ries familiar to readers with a psychological background – the ‘Robber’s Cave’ study,Piaget’s developmental theory, Bartlett’s research on memory to name but three Wehave also, where possible, organised the chapters in this way: developmental psy-chology, social psychology, individual differences, cognitive psychology and so on.This said, we also explain the traditional psychological concepts too, so the bookwill be accessible to anybody with an interest in evolutionary psychology whatevertheir background

theo-xx Preface to the third edition

Pedagogical features

We hope that the book’s greatest pedagogical feature is the book itself We have tried

to explain the relevant concepts and research as clearly as we can We also hope that

we have tried to convey our enthusiasm for evolutionary psychology tempered with

a critical eye when we think things don’t quite add up In addition to this we have

included extra critical thinking questions at the end of each chapter which can be

used – for example – for seminar discussion points Perhaps the biggest change from

previous editions is that we have written 240 multiple-choice questions (twenty per

chapter) for either formative or summative assessment

Acknowledgements

Finally, once again we would like to take this opportunity to thank all of the tors and students who have made use of the first and second editions of our bookand in particular to those who have provided useful feedback In particular we wouldlike to thank Richard Andrew, Gordon Bear, Jannes Eshuis and Fred Toates At Cam-bridge University Press we would especially like to thank Valerie Appleby, MartinBarr, Joanna Breeze, Charles Howell, Hetty Marx and Carrie Parkinson

instruc-1 Introduction to evolutionary psychology

K E Y C O N C E P T S

the Environment of Evolutionary Adaptedness (EEA) • proximate and ultimate levels of explanation • the inheritance of acquired characteristics • particulate inheritance • eugenics • the Great Chain of Being (scala naturae) • sociobiology

• modularity

Evolutionary psychology is a relatively new discipline that applies the principles of winian natural selection to the study of the human mind The principal assumption of evolutionary psychology is that the human mind should be considered to be an organ that was designed by natural selection to guide the individual in making decisions that aid survival and reproduction This may be done though by species-specific ‘instincts’ that enabled our ancestors to survive and reproduce and which give rise to a universal human nature But equally the mind is an organ which is designed to learn, so – contrary to what many people think – evolutionary psychology does not suggest that everything is innate In this chapter we trace the origins of evolutionary psychology, and present some of the argu- ments between those who hold that the mind is a blank slate and those who believe that human behaviour, like that of other animals, is the product of a long history of evolution.

Dar-The origins of evolutionary psychology

The fundamental assumption of evolutionary psychology is that the human mind

is the product of evolution just like any other bodily organ, and that we gain abetter understanding of the mind by examining evolutionary pressures that shaped

it Why should this be the case? What can an understanding of evolution bring topsychology? After all, scientists were able to learn a great deal about bodily organssuch as the heart and the hand long before Darwin formulated the theory of naturalselection Unfortunately, not all body parts are as easy to understand as heart andhand A classic example is the peacock’s tail This huge structure encumbers the

2 Evolutionary Psychology

animal to the extent that it makes it difficult to escape from predators and requires aconsiderable amount of energy to sustain it – energy that might otherwise be used forreproduction Darwin was similarly troubled by this and in a letter to his colleagueAsa Gray remarked that ‘The sight of a feather in a peacock’s tail, whenever I gaze at

it, makes me sick’ (Darwin, 1859) Or to take another even more perverse example, the

male Australian redback widow spider (Latrodectus hasseltii) who sacrifices himself to the female following copulation: why would you design an animal to do that? These

types of questions are known as ultimate questions as they ask why a particular behaviour exists at all These are usually contrasted with proximate questions which

ask about, for example, how a particular behaviour develops, what are its neural orcognitive underpinnings or whether it is acquired or innate

The answers to these questions highlights a deep-rooted problem in the foundations

of traditional psychological thinking To the extent that psychologists ever considerwhy we perform particular behaviours – and this, admittedly doesn’t happen veryoften – they usually concern themselves with the benefit to the individual whoperforms the behaviour But current Darwinian theory turns this thinking on its head

We are not necessarily the beneficiaries of our own behaviour: the beneficiaries ofbehaviour are, in many cases, our genes

It is worth pausing for a second to reflect upon this point and considering itsimplications The peacock dragging his tail behind him might well prefer – should

he be able to consider such things – to be rid of it The male redback widow spidermight choose, on reflection, to forgo indulging the cannibalistic urges of his erstwhilesqueeze But placing the individual at the centre of the action in this way doesn’talways give us the complete picture Modern evolutionary theory sees the individual

as merely an ephemeral and transient bit-player in the theatre of existence, actingout a script that was not of his or her writing, a script written in the language

of the genes Richard Dawkins probably best summarised this when he made thefamous replicator–vehicle distinction (see chapter 2) ‘We are survival machines –robot vehicles blindly programmed to preserve the selfish molecules known as genes’(Dawkins 1976, p xxi) If you think about it this has to be the case Life originatedfrom replicating chemicals – precursors of DNA – and only after many millions ofyears did these chemicals start to build structures around them to form the precursors

of cells: unicellular organisms became multicellular, tissue became organs until weeventually ended up with animals with brains and behaviour So bodies and brainsclearly benefited DNA otherwise they wouldn’t have been produced; they would havebeen outcompeted by the brainless and the bodiless So our genes aren’t for ourbenefit, we are for their benefit Dawkins goes on to say ‘[t]his is a truth which stillfills me with astonishment’ If you aren’t astonished, you haven’t understood it, butdon’t worry, we discuss this further and in greater depth inchapter 2

It is worth adding a caveat to all of this: the above only applies to evolved behaviour(or organs); any behaviour which has not evolved, such as a purely learned behaviour,

may not benefit genes at all Deciding exactly which behaviours are evolved andwhich are not (and which are a bit of both) is a difficult task and one to which wereturn many times throughout the subsequent chapters.

In terms of psychology, we have only scratched the surface in trying to applyevolutionary thinking to understanding behaviour Many of the ideas expressed inthis book will doubtless be proved wrong in the fullness of time, but if we are toproperly understand humanity in all its shapes and sizes, loves and hates in sanityand madness, then we need an understanding of basic evolutionary principles and,

in particular, the gene-centred view of life

It is said that science has presented humans with three hammer blows to its sense

of self-importance Copernicus taught us that the Earth was not at the centre of theuniverse; Freud showed us that our instincts are emotional and sexual rather thanrational and godly; and Darwin demonstrated that we were descended not from angelsbut from apes To this we might add the gene-centred view of life which shows that

in many cases we are not the final beneficiaries of our own behaviour; the buck stopsnot with us but our genes

A history of evolutionary thinking

Evolution before Darwin

For millennia humans have been fascinated by the natural world, not just the plexities of the organisms that constitute it, but the interdependencies that existbetween different species Flowers provide food for insects that are eaten by birdsthat are consumed by small mammals that are preyed upon by larger animals thateventually die and provide food for the plants that produce flowers and so the cyclecontinues Surely such a complex system could not have arisen by accident? Surelythis must have somehow been designed, created by some all-powerful being? Theidea that nature in all its complexity was created all at once held sway for a longtime, not just as religious doctrine but as a true account of the origin of Everything

com-It still does hold sway in the minds of many today Debates about the scientific status

of creationism and intelligent design have recently approached boiling point and, inthe United States, entered the courtroom In December 2005 Judge John Jones ruledthat intelligent design was not science and therefore it is not permissible to teach

it as science in the classroom More recently the so-called ‘new atheist’ movement,headed by Daniel Dennett, Richard Dawkins, Sam Harris and the late ChristopherHitchens (sometimes referred to as the Four Horsemen) have written provocative and,

in some cases, inflammatory anti-religious texts However, the purpose of bringing

up religion in this chapter is not to ultimately bury it, but to show how many religions

4 Evolutionary Psychology

were grappling with the same problems as many scientists: to understand where lifecame from, and what it means

Not every ancient belief system proposed steady states and immutability The

Ancient Greek philosopher Thales (c.624–545BC) tried to explain the origins of life interms of natural as opposed to supernatural terms He also proposed that life ‘evolved’out of simpler elements with the most basic element – from which all else ultimatelyderived – being water Later another Ancient Greek, Empedocles (495–435BC), sug-gested that in the beginning the world was full of bodily organs which occasionallycame together and joined up, driven by the impelling force of Love The results ofmost of these unions were ‘monstrosities’ and died out, but a minority were suc-cessful and went on to reproduce, producing copies of themselves Although we canclearly recognise this as being fanciful in that we now see love as a human emotionrather than as an impelling force of nature, Empedocles’ mechanism has conspicuoussimilarities to natural selection (see chapter 2) In particular, the idea that changeoccurs over time by a gradual winnowing of less successful forms Aristotle (384–

322 BC) seemingly killed off evolutionary thinking for some time by proposing thateach species occupied a particular space in a hierarchical structure known as the

Great Chain of Being or scala naturae In this scheme, which was later adopted by

the Christian religion, God occupied the topmost rung of the ladder followed by

angels, then the nobility (males then females), then ordinary men, ordinary women,

animals, plants and finally inanimate objects Moving from one rung to anotherwas not permitted which meant that there was a natural order of things Aristo-tle’s view was not merely descriptive (describing the way the world is) but was also

prescriptive (this was deemed to be the way the world should be) so any change

to the established hierarchy would lead to chaos until the order was re-established

By fixing the hierarchy in this way Aristotle’s view effectively closed down debateabout evolutionary change, not only would such an approach be considered theo-retically incoherent, it was also considered morally wrong to question the waythings should be

Much more recently in 1798 the German philosopher Immanuel Kant wrote in his

work Anthropology that:

[A]n orang-utan or a chimpanzee may develop the organs which serve for walking, graspingobjects, and speaking – in short, that he may evolve the structure of man, with an organ forthe use of reason (Kant,1798)

In direct contradiction of Aristotle, Kant imagines how one organism can changeover time, perhaps acquiring the characteristics of other organisms Notice also thatKant does not merely refer to physical change: ‘an organ for the use of reason’ is

a psychological faculty In this way Kant presaged evolutionary psychology by twocenturies

Figure 1.1 Erasmus Darwin

Darwin’s own grandfather, Erasmus Darwin (1731–1802), wrote that all livingthings could have emerged from a common ancestor (what he called ‘one livingfilament’) He also suggested that competition might be the driving force behindevolution He saw this competition occurring between different species and within aspecies between members of the same sex (presaging the theory of sexual selection

proposed in 1871 by his grandson) In The Laws of Organic Life, he states:

The final course of this contest among males seems to be, that the strongest and most activeanimal should propagate the species which should thus be improved (Darwin, cited in King-Hele,1968, p 5)

Although we can see close similarities between these ideas and Darwin junior’s theory

of evolution, Erasmus failed to produce a plausible mechanism for evolutionarychange

A contemporary of Erasmus Darwin, Jean-Baptiste Lamarck (1744–1829), proposedjust such a mechanism to account for change Lamarck’s first law suggested thatchanges in the environment could lead to changes in an animal’s behaviour which,

in turn, might lead to an organ being used more or less The second law was that suchchanges are heritable Taken together these laws prescribe an organism’s continuousgradual change as the result of the interaction between the organism’s needs and the

environment Most evolutionary biologists agree that the inheritance of acquired

characteristics, as Lamarck’s theory has since been called, is incorrect Although the

environment can indeed affect bodily organs, for example increased exercise canincrease the capacity of the heart and lungs, such changes cannot be passed on to

6 Evolutionary Psychology

the organism’s offspring Although Lamarck’s theory has fallen from favour, CharlesDarwin did cite Lamarck as a great influence in the development of his theory ofevolution: natural selection

Darwin and natural selection

Natural selection depends on two components: heritable variation (individuals within

a population tend to differ from each other in ways that are passed on to their

offspring) and differential reproductive success (as a result of these differences some

individuals leave more surviving offspring than others) You can see this processlaid bare in asexual species where an individual reproduces simply by producing anidentical copy of itself In such cases, the overwhelming majority of offspring will

be identical to the parent, but a few will be different in some way due to errors inthe copying process Should these different offspring survive and reproduce, then the

majority of their offspring will be identical to them and the process repeats itself.

However, copying errors seldom have positive consequences To see this, imaginethat you make an error copying down a recipe: there is a good chance that thiserror will make no noticeable difference to the end product (for instance you mightadd two grinds of pepper rather than one) On the other hand, it may make the endproduct substantially worse (adding a tablespoon rather than a teaspoon of salt);only very rarely will an error actually improve the recipe Similarly, in the naturalworld, copying errors would probably have no effect or would lead to the individualfailing to pass on its genes On very rare occasions, however, an error might produce

an organism that is actually better fitted to the environment than its parents or itmight be able to exploit some property of the environment that its ancestors couldnot In such cases, barring unfortunate random accidents, this individual will tend

to produce more offspring and the ‘error’ will soon become the norm In some casesthe new lineage might outcompete the old, and come to replace it In other cases,particularly if the two variants become geographically separated, both versions mightcoexist and ultimately form two different species

As we shall see inchapter 3, the state of affairs is somewhat more complicated fororganisms that reproduce sexually For asexual species, variation only comes fromcopying errors (or mutations) Sexually reproducing species combine the genes of twoindividuals during reproduction, meaning that offspring will always be different fromeither parent The increased variation produced by sexual reproduction is thought to

be one of the reasons why sex evolved in the first place

Mendel and the birth of genetics

Darwin knew nothing about genetics, and for good reason: at the time of Darwin’sdeath, no one on earth knew about genetics except the Austrian monk Gregor Mendel

Figure 1.2 Gregor Mendel

Between 1858 and 1875 Mendel conducted a series of breeding experiments on hybridpea plants in the garden of his monastery in Brunn

One of Mendel’s greatest insights was that inheritance was particulate Darwin

presumed that the traits of an individual were some sort of blend of the traits of themother and father, as might happen when mixing paint Some observations seem tosupport this belief In many species, the result of a mating between a comparativelylarge female and a small male will tend to produce offspring whose size is somewhere

in between the two: a fact that animal breeders had known for some time Mendeldemonstrated that the blend model is incorrect He found that if two pea plants werecrossed, one having white flowers and one having red flowers, the offspring would

8 Evolutionary Psychology

be either red or white, never pink, as might be expected if the two traits blended Thereason why some traits, such as height or skin colour, seem to blend is because theyare controlled by a number of genes, for traits controlled by single genes, inheritance

is always particulate

In truth, it probably didn’t need Mendel’s data to highlight the inadequacies ofthe blend model Any child who has mixed the colours in a paint set will soon realisethat after a few mixes you always end up with the same dirty brown colour Likewise

if sex merely blended traits, after a sufficiently large number of generations everyonewould end up being the same, reducing variation Since natural selection depends

on variation to work, evolution would soon grind to a halt Darwin was certainlyaware of the shortcomings of the blend model (Dawkins,2003), but did not produce abetter theory to replace it, although he did come close; in a letter to his friend AlfredWallace (and co-discoverer of the theory of natural selection) in 1866 he wrote that:

I crossed the Painted Lady and Purple sweetpeas, which are very differently coloured varieties,and got, even out of the same pod, both varieties perfect but none intermediate [ ] [T]ho’these cases are in appearance so wonderful, I do not know that they are really more so thanevery female in the world producing distinct male and female offspring

Unfortunately Darwin never made the next step that would have enabled him tounderstand the true mechanism of inheritance, nor, it seems, was he aware of Mendel’swork There were rumours that Darwin possessed a copy of the journal containingMendel’s article ‘Versuche ¨uber Pflanzenhybriden’ (‘Experiments in plant hybridisa-tion’) but no copy was found in Darwin’s extensive library now housed at CambridgeUniversity Generally, the scientific community was rather slow to realise the signif-icance of Mendel’s ideas and biology had to wait until the twentieth century beforeMendel’s work was rediscovered The subsequent fusion of genetics and evolution-ary theory led to what in biology has become known as ‘the modern synthesis’ (seechapter 2)

From evolution to evolutionary psychology

Although most of Darwin’s examples in The Origin of Species concerned physical

traits, he also believed that natural selection had a role to play in the evolution ofbehaviour Darwin appeared to see the human mind as being explainable by the samefundamental physical laws as other bodily organs, in terms of mechanistic principles

In one of his early notebooks, written in 1838, he speculated that:

Experience shows the problem of the mind cannot be solved by attacking the citadel itself –

the mind is function of body – we must bring some stable foundation to argue from.

That stable foundation was materialism, the approach adopted by modern cognitive

psychology that sees the mind as being ultimately reducible to the activity of the

brain, or as Steven Pinker puts it, ‘the mind is the information processing activity ofthe brain’ (Pinker,1997) This materialism is important to evolutionary psychologybecause if the mind is just the activity of the brain, then the brain, being a physicalorgan, is subject to the pressures of natural selection Therefore the mind and hencebehaviour is also, at some level, the product of evolution by natural selection (seechapter 9).

Darwin did make some forays into psychology In The Expression of the Emotions

in Man and Animals (1872; see chapter 11 in this book), Darwin theorises on the

evolutionary origins of emotions and their expressions In 1877 Darwin wrote A Biographical Sketch of an Infant based on his observations of his infant son This last

work, however, is largely descriptive and although it speculates on the instinctualbasis of early crying and sucking behaviours, it makes no mention of the role ofevolution and natural selection in shaping such behaviours

Early attempts at an evolutionary psychology

Francis Galton

Figure 1.3 Sir Francis Galton

Darwin’s cousin (also a grandson of Erasmus Darwin) Francis Galton (1822–1911)(seefigure 1.3) was much influenced by the theory of natural selection:

10 Evolutionary Psychology

The publication in 1859 of the Origin of Species by Charles Darwin made a marked epoch

in my own mental development, as it did in that of human thought generally Its effect was

to demolish a multitude of dogmatic barriers by a single stroke, and to arouse a spirit ofrebellion against all ancient authorities whose positive and unauthenticated statements werecontradicted by modern science (Galton,1908, p 287)

Galton was a very important figure in the history of psychology; he proposed thatcharacter and intelligence were inherited traits and developed some of the first intel-ligence tests to explore these issues He was, in many respects, the father of what

is now known as psychometrics He also anticipated the method of experimentalpsychology by emphasising the need to use quantitative data from large samples ofindividuals Galton also proposed that traits that may have been useful in ances-tral times might be less useful in contemporary (in this case, Victorian) society Forinstance, he suggested that during ancestral times evolution had favoured humanswho were group-minded or gregarious Humans live in groups, he reasoned, so thosewho thrived under such circumstances would leave more surviving offspring thantheir less gregarious counterparts However, in Galton’s time, when greater emphasiswas placed upon self-reliance and personal industry, gregariousness might be a lessdesirable trait (seechapter 13)

The argument that traits that were important in hunter-gatherer communitiesmight be suboptimal in contemporary society is a familiar one in modern evo-lutionary psychology Such an observation is comparatively uncontroversial andshould be judged as a scientific theory that stands or fails on the basis of theevidence More controversial was Galton’s attempt to apply his scientific findings

to help the greater good of society He suggested that one way that society might

be improved would be to engage in a little selective breeding He suggested thatthose individuals whose traits might benefit society (the innovators, the highlyintelligent, etc.) be encouraged to produce many offspring, and those whosetraits are seen as less desirable (the less intelligent, the indolent, etc.) be discour-

aged from reproducing, a controversial programme that he called eugenics (see

box1.1)

William James and the concept of instinct

William James (1842–1910) is one of the most influential psychologists of alltime He made the distinction between short- and long-term memory used to thisday by modern cognitive psychologists, studied attention and perception, had akeen interest in the nature of consciousness and was also very much interested inapplying Darwin’s ideas to human psychology In particular he outlined instinctssuch as fear, love and curiosity as driving forces of human behaviour and proposedthat:

Box 1.1 Eugenics

The word ‘eugenics’ coined by Francis Galton comes from the Greek wordeugenesmeaning ‘well born’ The idea was also Greek InThe Republic Plato proposed thatalthough friendships between the sexes should be permitted, procreation should becontrolled by the government with the aim of breeding a better society In a sense, allsexual beings participate in a form of eugenics, albeit unconsciously There is evidence

to suggest (see chapters3and4) that when an animal (including a human animal)selects a sexual partner it does so, among other things, on the basis of characteristicsthat are indicative of good genes Good looks, it appears, are not arbitrary But

eugenics is rather more than that; it was developed as a method of trying to dictatewho breeds with whom and, in extreme cases, who doesn’t breed at all

There are two forms of eugenics, often called positive and negative Positive eugenicsoperates by encouraging people with high fitness to mate together and produce manyoffspring The word ‘fitness’ here is used in a quasi-Darwinian sense, and can be treated

as meaning ‘possessing characteristics which are thought to be good for society’ This

is probably the most benign form of eugenics although it has to be said that even thisform of eugenics is anathema to most people Negative eugenics, on the other hand,attempts to curtail or prohibit reproduction among those who are considered unfit.When Galton founded the Eugenics Education Society in 1907 (later the Eugenics

Society and finally the Galton Society in 1989) the goal was to improve the humanspecies by positive means:

If a twentieth part of the cost and pains were spent in measures for the improvement ofthe human race that is spent on the improvement of the breed of horses and cattle, what

a galaxy of genius might we not create! We might introduce prophets and high priests ofcivilization into the world, as surely as we can propagate idiots by matingcretins Menand women of the present day are, to those we might hope to bring into existence,what the pariah dogs of the streets of an Eastern town are to our own highly bred

varieties (1864, pp 165–6)

Charles Darwin’s son Major Leonard Darwin took over the eugenics society from Galtonand instigated the transition from positive to negative eugenics He proposed that apolicy of segregation should be implemented whereby the fit were separated from theunfit ‘Compulsion is now permitted if applying to criminals, lunatics, and mental

defectives; and this principle must be extended to all who, by having offspring, wouldseriously damage future generations’ (L Darwin,1925)

In the early part of the twentieth century, hundreds of thousands of people were

sterilised worldwide on the grounds that they were deemed psychologically unfit In theUnited States alone it was reported that by 1960 almost 60,000 individuals had

undergone involuntary sterilisation (Reilly,1991) Undoubtedly the largest and most

12 Evolutionary Psychology

systematic programme of eugenics occurred in Nazi Germany Beginning withsegregation and sterilisation and finishing with the systematic slaughter of millions,Hitler tried to ensure that the genes of the ‘unfit’, mainly Jews but many others as well,would not make it to the next generation

Curious to think in these post-holocaust days that eugenics was once considered to be

a respectable enterprise Members of eugenics societies included the eminenteconomist John Maynard Keynes; John Harvey Kellogg of Kellogg’s corn flakes fame;Lord William Henry Beveridge, producer of the Beveridge report on social insurance inthe United Kingdom; psychologists Cyril Burt, Hans Eysenck and Charles Spearman; thesexologist H Havelock-Ellis; and geneticist Ronald Fisher

Undoubtedly, many eugenicists probably felt that they had humanity’s best interests atheart However, today most would probably feel that even positive eugenics with itsattempt to coerce or interfere with an individual’s freedom of choice of sexual partner

is an infringement of civil liberties and therefore abhorrent Eugenics societies are stillwith us today, but technology has presented us with different if related issues Currentlythere is controversy about the role of genetic engineering in determining human traits

It is already possible to screen foetuses for genetic disorders, and soon it will bepossible to replace ‘defective’ genes to produce a healthy infant Such gene therapy, as

it has been called, has been heralded as being of potential benefit for humanity, butsome worry that genes might be replaced that are not medically deficient, merelyundesirable If it were possible to detect genes that influence criminality, or antisocialpersonality, would it be ethical to change such genes for the common good? Would it

be morally right to genetically manipulate genes for intelligence, or good looks?The eugenics controversy has cast a shadow over the use of Darwinian theory inexplaining human behaviour (see box1.3); it has been all too easy for all evolutionarytheories to be dismissed as inherently racist, supremacist or otherwise politicallyincorrect This is unfortunate Darwinian thinking could well prove to be the frameworkthat unites the social sciences (Wilson,1998) in the same way that it unified thedisparate areas of biology in the early part of the last century (seechapter 2) We mustnot reject it simply on the grounds that some people have used it for nefarious means,any more than we should reject sub-atomic physics for its role in the production ofnuclear weaponry The fact that we do not like the implications of a particular theorydoes not affect its truth On the other hand, it would be a mistake to think that scienceexists in a vacuum, and it is incumbent on all of us – including scientists, perhapsespecially scientists – to guard against those who might wish to use the results ofscience for their own political ends

Nothing is commoner than the remark that man differs from the lower creatures by the almosttotal lack of instincts and the assumption of their work by reason (James,1890, p 389)

He went on to add that human behaviour might be characterised by more instinctsthan other animals rather than fewer, an idea that has been embraced by modernevolutionary psychologists such as John Tooby and Leda Cosmides James’s argumentrelating to instincts was so influential that in 1921 psychologist Ellsworth Faris, acritic of the instinct approach, was able to comment that:

So well did he [James] argue for the existence of instincts in man that we may now say:Nothing is commoner than the belief that we are endowed with instincts inherited from thelower creatures Whole systems of psychology have been founded on this assumption (1921,

p 184)

Many students of psychology know of William James’s work on memory, attention,consciousness and learning, but his views on instincts are less widely known Infact, the concept of instinct was dropped from social scientists’ terminology in thetwentieth century partly because it was considered too imprecise a term to be sci-entifically meaningful (see Bateson,2000) Furthermore, many so-called instinctivebehaviours are capable of being modified by experience, in which case it is difficult

to see where an instinct finishes and learning begins A final reason why the concept

of instinct fell out of favour is that a new approach to the social sciences denied theirexistence and saw culture rather than biology as being the principal determiner ofhuman behaviour This is what we turn to next

The rise of culture as a causal force in human behaviour

Two of the instigators of the recent emergence of evolutionary thinking in psychology,John Tooby and Leda Cosmides, have called the traditional non-evolutionary socialscience approach the Standard Social Science Model (SSSM) The SSSM makes thefollowing assumptions about human behaviour and culture

r Humans are born as blank slates: knowledge, personality traits and cultural valuesare acquired from the cultural environment

r Human behaviour is infinitely malleable: there are no biological constraints as tohow people turn out

r Culture is an autonomous force and exists independently of people.

r Human behaviour is determined by a process of learning, socialisation or nation

indoctri-r Learning processes are general in that they can be applied to a variety of nomena The same processes underlie mate selection, for example, as underlie foodselection

phe-14 Evolutionary Psychology

Many of these ideas can be seen in the work of anthropologists such as MargaretMead, sociologists such as Emile Durkheim and psychologists such as Albert Bandura.The establishment of the SSSM can be seen, at least in part, as a reaction to some ofthe more extreme claims of the biological determinists of the late nineteenth and earlytwentieth century (see box1.1) Many took Darwin’s theories and used them to demon-strate that certain races were less highly evolved than others When experiments wereperformed to test these ideas they usually took the form of presenting individualsfrom such cultures with Western-style intelligence tests On finding that the respon-dents tended to fail such tests spectacularly, it was adduced that this was evidencethat they occupied a lower rung on the evolutionary ladder than did the people ofthe West Of course, these studies were fundamentally flawed in that the tests wereculturally specific, requiring individuals to spot missing components from gramo-phones and tennis courts (see Gould,1981) Such ideas were common in The History

of Creation, in which the great biologist and naturalist Ernst Haeckel stated that

The difference in rationality between a Goethe, a Kant, a Lamarck, a Darwin and that of thelower natural men – a Veda, a Kaffer, an Australian and a Papuan is much greater thanthe graduated difference between the rationality of these latter and that of the intelligentvertebrates, for instance, the higher apes (1969)

Eugenicists and their kind used the results of such research to recommend all manner

of atrocities such as forced sterilisation based on the premise that other races andcultures were not so ‘highly evolved’ and therefore wouldn’t feel, for example, pain

in the same way that the ‘more evolved’ Western people would

This is a misunderstanding of Darwin’s ideas In fact, the notion that some isms are ‘more evolved’ than others and therefore more important in some moral waydates back to Aristotle and the Great Chain of Being (see above) As we shall see

organ-in more detail organ-in later chapters, Darworgan-inian thorgan-inkorgan-ing explicitly denies such a notion.Humans are not descended from chimpanzees as is commonly thought; rather, chim-panzees and humans are both descended from a common ancestor It is all too easy

to believe that a chimpanzee is simply a more primitive version of a human, stripped

of the bells and whistles that constitute humanity On the contrary, chimpanzees byvirtue of the nature of their evolutionary trajectory have their own particular adapta-tions (including, no doubt, psychological adaptations) that we do not As an analogy,the railway train and the automobile share a common ancestor – the horse-drawncart – but it makes no sense to assume that a car is a more sophisticated railwaytrain (or vice versa) since each has its own specific adaptations to suit the purposefor which it was designed

Cultural relativity

The founder of what was to become cultural relativism was the anthropologist FranzBoas (seechapter 14) Boas argued that many differences between people were due

Figure 1.4 Chimpanzees have specialised adaptations of their own

to differences in their culture and if one wished to understand people one mustnecessarily understand their culture This represented a step change in the socialsciences that is still of great importance today No longer do we assume that,for instance, working-class people speak differently from middle- and upper-classpeople because they are biologically inferior; we know now that it is an effect ofculture

16 Evolutionary Psychology

From these honourable beginnings cultural relativism dominated thinking to theextent that many social scientists developed an almost pathological fear of biologi-cal explanations of human behaviour, a disposition that sociologist Lee Ellis (1996)

termed biophobia There are various reasons for this One is that once a scientific

paradigm is established it is difficult for researchers to consider alternative tions that lie outside the paradigm as they are seen as old ways of thinking Another

explana-is that the eugenic atrocities of the Second World War made people fearful of sure; advancing explanations based on human nature was seen as advocating genetic

cen-determinism and eugenics, as the sociobiology movement soon discovered (see next

section and box1.3)

Despite the misgivings of the social scientists, outside psychology Darwinianthinking was alive and well in disciplines such as ethology (Tinbergen, 1951) andbehavioural ecology (Krebs and Davies,1978) (see box1.2), but the orthodoxy withinpsychology was still cultural relativism Even psychologists who studied animalbehaviour – where Darwinism can be least controversially applied – tended to ignorespecies-specific behaviour Learning theorists such as Pavlov, Watson and Skinnerwere concerned with studying the general mechanisms of learning, using the prin-ciples of classical and operant conditioning This framework viewed human beings

as just more complex versions of rats, pigeons and sea slugs and proposed that if

we could understand these simpler organisms, then we could scale up the findings tounderstand humans Interestingly, two researchers engaged in this enterprise, Kellerand Marian Breland, found that animals’ instinctive behaviour kept getting in theway of the supposedly species-general processes of association and reinforcement.Using Skinnerian methods they were engaged in training animals for the advertisingindustry teaching different animals to put dollars in piggy banks, for example Whatthey found was that despite their best efforts the animals kept reverting to instinctivebehaviours instead of depositing them in the container as required: pigs attempted toroot the dollars with their snouts (a natural pig behaviour) whereas raccoons wouldrub the coins together (an instinctive food-washing behaviour) Breland and Breland(1961) open their paper by stating that:

There seems to be a continuing realization by psychologists that perhaps the white rat cannotreveal everything there is to know about behavior (p 1)

It would be incorrect to attribute the failure of psychology to embrace Darwin asresulting solely as a result of the political correctness of the dominant cultural rel-ativist school Psychologists have tended to focus on proximate questions such as

‘how do people form impressions of other people?’, or ‘how does memory work?’ or

‘what risk factors are important in the development of eating disorders?’ rather thanthe ultimate questions for which a Darwinian framework is best suited Given thetypes of questions that concerned psychologists cultural relativism – or what Toobyand Cosmides refer to as SSSM – provided a perfectly workable framework; there was

behaviour The danger is that although there are differences in approach, subject

matter and method there is a great deal of overlap too The descriptions below shouldtherefore be seen as a rough guide rather than the final word on the matter

Ethology

Description

The term ethology is derived from the Greek ethos meaning character or habit

Although many people see ethology as the invention of Lorenz, Tinbergen and vonFrisch, during the 1930s, the term has been around for at least 300 years What Lorenz,Tinbergen and von Frisch did was to take a largely descriptive discipline and add

academic rigour to it via systematic observation and recording of behaviour followed

in a given environment These models are then used to derive predictions and

compared against actual animal behaviour

While sociobiologists and evolutionary psychologists tend to emphasise genetic

constraints, behavioural ecologists emphasise the flexibility that genes provide In thisway ecological pressures select behavioural responses

Key figuresGeorge Williams, John Maynard Smith, John Krebs, Irven DeVore, Donald Symons,Richard Alexander, Nicholas Davies, Richard Dawkins, Robin Dunbar.

Sociobiology

DescriptionThe term sociobiology had been around for at least twenty years before E O Wilsondefined it more rigorously in his bookSociobiology: The New Synthesis as ‘thesystematic study of the biological basis of all social behaviour’ Grew out ofdevelopments in ethology during the 1960s and 1970s Very much overlaps withbehavioural ecology – in fact most of the names listed under sociobiology could alsoappear under behavioural ecology and vice versa

ApproachDeals with the evolution of social behaviour and uses functional explanations of pro-and antisocial behaviour The term functional is used here to mean how currentbehavioural responses occur because of the usefulness they had to an individual’sancestors Considers human social organisation developed through natural selection.Most sociobiologists are interested in non-human species – but applying the conceptsfrom this area to explain human behaviour led to heated debate during the latter years

of the twentieth century

Key figuresEdward O Wilson, William Hamilton, Robert Trivers, Randy Thornhill, Margo Wilson,Martin Daly, David Buss

Evolutionary psychology (Santa Barbara school)

DescriptionThe birth of evolutionary psychology was marked by the publication ofThe AdaptedMind It generally takes the principles of sociobiology and combines them with a