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Evolutionary Psychology


Dr Richard Stevens


Richard Stevens, The Open University

Evolutionary psychology, with its highly articulate supporters and passionate opponents, is currently creating a few shock waves in the otherwise sedate world of British psychology. Even if you haven't come across this approach to psychology before, you will have undoubtedly encountered many explanations of human behaviour which draw on its assumptions. What evolutionary psychology tries to do is help us understand the ways in which we think and behave in terms of their adaptive value in our evolution. It applies the principles of evolutionary theory to understanding human behaviour and cognition.

Darwin's foundation
Charles Darwin, of course, laid the foundation for our understanding of evolutionary process. Darwin realised that the characteristics of organisms can be passed on through generations by a process of inheritance, and that change could enter this process by spontaneous mutations and also by the mixing of what we now call genes through sexual reproduction. His great breakthrough, stimulated by his observations of different species on different islands in the Galapagos, is the idea of selection. Whether or not a new variation will succeed in terms of being repeated in subsequent generations will depend on whether or not an animal survives
(natural selection) and to what extent it reproduces and leaves surviving offspring who will reproduce in their turn (sexual selection). Darwin himself produced a wealth of evidence to support his ideas (This included fossil remains, the geographical distribution of plants and animals and the physiological and anatomical structures of living species). This evidence has been added to subsequently and the genetic processes underpinning Darwin's ideas have been clarified, so that now, although there may some dispute over details, there are few biologists who would not accept the broad principles that Darwin espoused.

It is evident that Darwin's thesis applies not only to the physical characteristics of different animal species but also to their behaviours such as feeding, courtship and mating, aggression and territoriality. Humans' physical characteristics may clearly be seen in an evolutionary light and we share something like 97% of our DNA patterning with chimpanzees. So we may well wonder how far evolutionary principles may help us in understanding human behaviour as well. Darwin himself thought human behaviour was no exception to the rule and in two books The Expression of the Emotions in Man and Animals (1872) and The Descent of Man (1874) which came after his seminal major work On the Origin of Species (1859), he detailed ways in which our characteristics, emotional expression and behaviours can be understood as inherited and the product of evolutionary processes.

A brief history of interest in the area
Although there was a lot of interest in 'human instincts' in early psychology (see, for example, William McDougall's classic psychology text of 1912), this became overtaken and discredited by the behaviourism which dominated psychology in the USA and to some extent in the UK through much of the twentieth century, with its emphasis on environmental influence on behaviour. This attitude was reinforced, quite independently, by a strong movement in social anthropology, with key figures such as Franz Boas and Margaret Mead who were also opposed to any attempt to see any human social behaviours as having a hereditary basis. After this long period of relative neglect, interest was subsequently generated in evolutionary understanding of behaviour in the 1970s by a sub-discipline known as sociobiology (e.g. Wilson 1975). Evolutionary psychology is the most recent and vigorous expression of this approach and has attempted in particular to understand the human mind in this way. This is certainly flourishing if controversial today in the UK and USA. Key thinkers in the area include not only psychologists but also biologists, philosophers, ethologists (those who study animal behaviour in the wild), archaeologists and social anthropologists as well.

What is evolutionary psychology?
Tooby and Cosmides (1992) define evolutionary psychology as psychology informed by the fact that the inherited structure of the human mind is the product of evolutionary processes. In other words, evolutionary psychologists assume that human abilities are the product of a long period of evolution and they are interested in understanding how and why our abilities have developed as they have. They argue that this approach may enable us to enhance understanding of our contemporary behaviour. Essentially evolutionary psychology seeks what is called a functional explanation, asking why a characteristic came to be the way it is - what are its origins in our evolutionary past. What, for example, were the evolutionary pressures which supported the development of spoken language in humans but not in chimpanzees? The argument is that if we can understand the kind of problems our ancestors had to solve in everyday life, then we should gain insight into the psychological processes that evolved to solve those problems.

As you can imagine this is no easy task. A major difficulty, for example, is that our ancestors aren't around for us to study them! All that is left of them are bones and a few tool artefacts. So what evolutionary psychologists essentially do is to use reason and inference to draw conclusions about the evolutionary bases of behaviour, working from a knowledge of the principles of evolution and a range of different kinds of evidence. These include the study of the behaviour of other animals, especially those close to ourselves such as apes, and relevant information from paleoanthropology (the study of physical and psychological characteristics of ancient, prehistoric humans and cultures) as well as observations of contemporary peoples who still live in hunter-gatherer fashion. A general strategy used by evolutionary psychologists has been described as a kind of 'reverse engineering' in that it is rather like using knowledge of mechanical principles and observations of the way a car operates to deduce how and why it was designed in that particular way. So we can use our knowledge of evolutionary principles and of past environmental conditions to identify the kind of cognitive and social capacities that would have been most effective for survival and reproduction in human prehistory.

An evolutionary basis to human cognition?
There is no question that in other species, highly complex patterns of behaviours are significantly governed by inherited genetic processes. So certain stimuli release particular patterns of behaviour, like for example, male sticklebacks respond aggressively to the colour red. Goslings, for a brief period in their early existence, will become imprinted on and follow the first moving object they encounter whatever that might be. And different species of birds show distinctive patterns of nest-building, courtship, breeding and parental behaviour.
With humans, the evidence is more elusive and inevitably involves a degree of informed speculation. There are clearly areas of our behaviour which are strongly influenced by genetic factors. Forms of basic emotional expression are common to all cultures (Ekman 1999) though the conditions which release them may be culturally variable. The usual patterns of laughter and crying are even found in children born blind and deaf.

There are two features which appear to be distinctively human - the spontaneous use of language and the possession of what is known as 'theory of mind'. At most, only the most rudimentary form of these abilities are found in other species and then only in those most closely related to us such as chimps. There have been good attempts to explain even these attributes in evolutionary terms. So, for example, Robin Dunbar (1996) has put forward the interesting thesis (and supported it with a range of evidence) that language may have evolved in humans because of its potential for social bonding. A particular mechanism for strengthening social ties among apes and monkeys is to engage in mutual grooming, picking out nits and generally cleaning another's fur. Dunbar argues that gossip serve a similar function of bonding in humans. However, it has the added advantage that you can chat with a whole group of individuals at any one time, rather than with just one other as would be the case with grooming.

Theory of mind is the rather peculiar term given to the human ability to 'mind -read', i.e. to infer the motives, attitudes and feelings of another - and to see them as a person with beliefs and intentions, rather than as an object. The argument here again has been that this capacity evolved in humans because of its adaptive value in facilitating our dealings with fellow members of our group.
One of the most developed analyses of the social origins of human intellect is in the work of Richard Byrne and Andrew Whiten (1988 and 1997) on 'Machiavellian intelligence'. They argue that intellect evolved in humans and apes because of its value in increasing social expertise. Cosmides and Tooby (1992) have also developed the idea of an evolutionary basis for human cognition by arguing and producing experimental evidence for the notion that there are key 'modules' in the mind which they claim developed because of
their adaptive potential to a social animal. One example they and their co-workers give is the universally found pattern of social exchange and reciprocity; so, if I give you something, then you are likely to feel some obligation on you to respond in your turn. Such social predispositions would have underpinned, for example, the exchange of food and forming alliances in early human history. Although the social currency of such exchanges will have changed through history and from culture to culture, the basic pattern, Cosmides and Tooby argue, is still evident in our behaviours today.

It has been suggested (Trivers 1972) that altruistic behaviour may also have evolutionary roots. A predisposition to help kin who are genetically related would, of course, be to help others whose reproductive success will serve to propagate similar genes to those of the benefactor. But altruistic behaviours towards those unrelated to us may also have had the pay-off that the recipient may reciprocate the favour at some other date and thus in this way have the potential to facilitate the benefactors reproductive capacity. Also, by being altruistic, a person may strengthen the social group on which she or he depends for survival.

The evolution of human social behaviour
There are good arguments for supposing that a range of social behaviours in contemporary humans have evolved because of their adaptive potential in the past. There is a lot of experimental research, for example, on the prevailing human tendency to favour the groups to which we belong and show hostility or indifference or hostility to out-groups (e.g. Tajfel et al.1971). This in-group/ out-group differentiation manifests itself widely in human social behaviour from the support of football teams and political parties to the rabid tribalism and factionalism we see in conflicts in the former Yugoslavia, Northern Ireland, Rwanda and that is such a feature elsewhere in the world. Some evolutionary psychologists such as Krebs (1998) have argued that even morality may have an evolutionary basis. Morality not only involves concern for others or altruism, but principles of justice which may have their origin in social contract modules. Morality also often contains an element of deference to authority arising from dominance hierarchies and subservience from subordinates which may well have had the adaptive value of enhancing social cohesion in our ancestral groups. Again, a wealth of social psychological studies have confirmed the strong human tendency for conformity and obedience (Milgram 1974). Other areas of human social behaviour to which evolutionary analysis have been applied include the ways in which our preferences for particular kinds of landscapes such as those by water or open savannah may have evolved because of their similarity to environments which had been conducive to survival in early human history.

Such evolved social behaviours can often be seen to be sustained by emotional feelings which have evolved to stimulate or constrain particular kinds of behaviour. Thus we may feel guilt or shame when we do not return a favour given to us, or the benefactor may feel anger towards us at our failure to reciprocate. Feelings of pride and loyalty may move us to support for in-group, while contempt may strengthen rejection of outgroups. Feelings of awe or admiration may strengthen our acceptance of the authority of charismatic leaders.

The nature of evolutionary process
In thinking about evolution, it is important to realize that it is not implied that animals or humans have developed in this way because they were aware that a particular way of behaving would lead to reproductive success. No intention or purpose is presumed on the part of the animals involved, either past or present. In broad principle, it is just that some characteristics and behaviours would be adaptive in promoting survival and reproduction and others would not. (It is a little more complicated than that in that some less adaptive behaviours may be related to and therefore 'carried by' other more adaptive ones). Genes which underpin adaptive characteristics and behaviours will thus be propagated in a way that the others will not.

Evolved psychological differences between men and women?
These principles would suggest that men and women may well have inherited somewhat different behavioural predispositions because, given the difference in the ways in which they reproduce, their optimal reproductive strategies (i.e. those behaviours likely to produce most offspring) are not the same. For human females have what evolutionary biologists call greater 'investment' in their offspring. In other words, considerable effort and energy is necessarily required for every infant they produce. This will involve at least a period of nine months gestation and most likely a long period of suckling and care, which means they can usually bear no more than one infant a year during a limited period of their lives. For males on the other hand, only a few minutes of copulatory activity may be required. The number of offspring they can produce is limited only by the availability of potential mates.

Evolutionary psychologists argue that this basic difference means that reproductive success for the two sexes would have been best achieved by rather different patterns of behaviour. As we are all the descendants of male and female ancestors who were successful reproducers (otherwise we wouldn't be here!) the different predispositions associated with reproductive success would have been selected for in this way in the past and would now therefore be characteristic of males and females today.

Given the relatively few offspring she could produce (and thus her greater reproductive investment), being choosy would have been very important for a female. For her, reproductive success must have crucially depended on her selecting circumstances, including a mate, which were likely to ensure that her relatively few offspring would survive to sexual maturity and so in their turn pass on her genes. For a male, however, with his far more extensive potential capacity to reproduce, number of matings would have been the critical factor. For if these were sufficiently frequent, and particularly if these were with fertile and healthy mates, this would have been an effective reproductive strategy, even if only a proportion of the offspring survived to sexual maturity.

This asymmetrical situation of female choosiness and male desire for varied and frequent mating means that men would be in competition for women who, in terms of sexual availability, were in shorter supply. One result of this male competition would be much greater variability in reproductive success among males than among females. For while the majority of females would have had little difficulty in ensuring that they had children (as males would be competing to mate with them), some males would have succeeded in fathering many children but quite a lot of others may well not have produced any at all.

One consequence of this would be that characteristics which promoted reproductive success in the face of competition, such as strength and size, would have been strongly selected for in males. Thus ancestral males evolved to have greater body weight and size in relation to females. In our species, men are on average 1.15 times bigger than women. The ratio in other species varies and (consistent with the reasoning above) appears to be related to the degree of sexual competitiveness. Chimps, for example, live in social groups where there is considerable variability in mating and competition for sexual partners; chimp males are about 1.3 times bigger than females. They also have, relative to body size, the biggest testicles of any primate - for the amount of sperm a male produces also offers a useful competitive advantage in such a situation. (It is worth noting that there are a few species of birds and fish where, for different reasons, male investment in the caring and rearing of offspring is greater than that of females. In such species, there is female competition for males and females are
likely to be the larger and more aggressive sex.)

Differential parental investment leads not only to male competition but to more subtle effects. It means, for example that, in humans, a crucial factor governing male reproductive success is female choice. Females have evolved to maximize their own reproductive success and their choice of mate in particular would need to have been consistent with this. Thus, according to evolutionary psychologists, one criterion would have been to select a mate whose own characteristics would increase the chance of producing healthy and reproductively successful children. Other characteristics looked for would have been factors like status and resources which would have ensured a protective base for the long process of rearing her children. But these would not be relevant unless the mate was prepared to commit such resources to the relationship and children, so male commitment would also have been a key criterion. In other words, those women who happened to choose men on the basis of such features would have been likely to produce most offspring and so such predilections would have been selected for in females.

The situation is complicated though by the fact that a specific feature of human females is 'hidden oestrus'. In other words, in contrast to other primates, there are no obvious signs of ovulation and they may mate at any time during the cycle even when this is unlikely to produce offspring. A consequence of this is that male paternity is only assured if no other male has sexual access. Human infants, for various reasons, also have a much longer period of dependency than do other primate infants. Both features imply that some form of sustained relationship with sexual partners may be reproductively advantageous for males. The fact that male paternity is never certain (Mama's baby, papa's maybe!) means that men have also become particularly sensitive to female sexual infidelity. The latter hypothesis has been tested by Buss (1989) in a cross-cultural study involving 37 countries. He and his co-workers found that, while both men and women experienced jealousy, men were significantly more likely to focus on sexual infidelity, while women's jealousy would be more likely to be centred on the emotional involvement of their partner with another.

The idea of different optimal reproductive strategies has been used to explain a range of observed differences between men and women. Men are more open to a variety of sexual partners, for example. They are by far the primary users of pornography and far more likely to go with prostitutes. Women, on the other hand, are more likely to look for status, achievement and resources in prospective partners.

Controversy and critique
Propositions such as these inevitably stimulate controversy. Some critics see the impact of evolutionary psychology on our thinking about people as potentially 'pernicious'. This view is in part based on the idea that if the predispositions proposed by evolutionary psychology constitute undesirable behaviour then, even to propose that such predispositions have some evolutionary and biological basis could have a negative impact on society and relationships between people. For there is then the risk that such ideas may be taken on board by people as facts about being human or being male and female and in this way become self-fulfilling. However, it has been counter-argued (see, for example, Buss 2000) that, rather than opposing evolutionary psychology on these kind of grounds, it would be far better to use the insights evolutionary psychology provides to try to ameliorate any negative effects that such differences or behaviours might potentially have.
Critics' views of evolutionary psychology are also sometimes based on what is known as the naturalistic fallacy. This is the false assumption that if predispositions are inherited then they are being asserted to be 'natural' and therefore 'good'. In fact, explanations of human social behaviour in terms of evolutionary origins do not, in themselves, justify any of the behaviours in question. The kinds of social behavioural patterns discussed above evolved because they happened to have adaptive and reproductive value under the particular conditions of early human existence. In no way do such origins provide moral justification for these behaviours. On the contrary, it may be argued that many behaviours which evolved in this way are no longer even functionally relevant or adaptive in the contemporary world. Ecological conditions change and the adaptations shaped by the totally different situations of the past may no longer work. They may even become a liability. So, for example, while in-group / out-group tendencies are likely to have promoted the survival of humans in our ancestral past, now in an age of atomic weapons they can pose a serious threat for the continuation of our species. Such a situation where a characteristic which was once adaptive becomes a liability because of changing circumstances is a major reason why more than 99% of all species that have ever lived are now extinct. And one reason why we may well now need in the present time to be wary with regard to some at least of the predispositions shaped by our evolutionary past.

A more telling critique of evolutionary psychology in my view is the argument that the development of language and complex thought and culture in humans gives our species a flexibility that can over-ride evolved predispositions. However, while it is true that human behaviours are in many respects plastic and variable from culture to culture, there is excellent research and general evidence that there are many universal features as well. Even given the distinctively human capacities for language and theory of mind, it would be surprising if some inherited predispositions of the kind that we find in other species did not to some extent apply to us as well. It is important though to realise that the scope of evolutionary explanations of human cognitive and social behaviour are circumscribed in that there are many areas of human social life to which they do not apply. And the explanations evolutionary psychology offers certainly need to be supplemented with an analysis of the ways in which cultural meanings and individual socialization can radically modify and construct the ways in which we behave and feel.

Finding out more
This gives you an overview of the kinds of areas which evolutionary psychologists have explored. If you want to find out
more about evolutionary psychology, the best source I would suggest is Lance Workman's superbly readable book (2014) Charles Darwin: The shaping of Evolutionary Thinking (Palgrave Macmillan Mindshapers Series). Another book very useful for background reading is Steven Pinker's How the Mind Works (1998). This is a highly readable, encyclopaedia and creative fusion of cognitive with evolutionary psychology but with the major emphasis (particularly once you get through the first few chapters) on the latter. Lance Workman himself will be one of the speakers at the conference on Evolutionary Psychology which OUPS are hosting in September of this year. This promises to be an exciting event which should really stimulate your thinking about ways of understanding the human condition.

Buss, D.M. (1989) 'Sex differences in human mate preferences: Evolutionary hypotheses testing in 37 cultures', Behavioural and Brain Sciences, vol.12, pp. 1-49.
Buss, D.M. (2000) 'The evolution of happiness', American Psychologist, vol.55, pp15-23.
Byrne, R.W. and Whiten A. (Eds.) (1988) Machiavellian Intelligence: Social Expertise and the Evolution of Intellect in Monkeys, Apes and Humans, Oxford: Clarendon Press.
Cosmides, L. and Tooby J. (1992), 'Cognitive Adaptations for Social Exchange' in J.H. Barkow, L. Cosmides and J. Tooby (Eds.) The Adapted Mind: Evolutionary Psychology and the Generation of Culture, Oxford, Oxford University Press.
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Dunbar, R.I.M. (1996) Grooming, Gossip and the Evolution of Language, London, Penguin.
Ekman, P. (1999) 'Afterword'. In C.Darwin, The expression of Emotions in Man and Animals (3rd Edition), London, HarperCollins.
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Trivers, R. (1971) 'The evolution of reciprocal altruism'. Quarterly Review of Biology, 46, pp.35-57.
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Whiten, A. and Byrne, R.W. (Eds.) (1997) Machiavellian Intelligence II: Extensions and Evaluations, Cambridge, Cambridge University Press.
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Workman, L (2014) Charles Darwin: the Shaping of Evolutionary Thinking, Mindshapers series, London, Palgrave Macmillan.
the Psychology of Well-being.

This article originally appeared in News & Views New Year 2016.


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