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Evolutionary Psychology

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1. The notion of the 'modularity of mind'
2. Evolution and Modularity
3. Recapitulation
4. Prospectus
5. Evolutionary Psychology
6. Machiavellian Intelligence

A great deal of contemporary work in psychology that draws on evolutionary theory does so in the paradigm of cognitive psychology (see lecture 15), and particularly within a line of thinking that views the 'mind' as modular. What does this mean?

1. The modular mind

'Cognitive Psychology' draws on the computer as a metaphor for the way in which to conceive of mental processes. It regards the brain as a machine for doing thinking, perceiving, and so on. Crudely put, the original model was of a 'general purpose' machine that built ways of dealing with problems presented by the environment:

According to this view, the same mechanisms are thought to govern how one acquires a language, how one learns to recognize emotional expressions, how one thinks about incest, or how one acquires ideas and attitudes about friends and reciprocity -- everything but perception. This is because the mechanisms that govern reasoning, learning, and memory are assumed to operate uniformly, according to unchanging principles, regardless of the content they are operating on or the larger category or domain involved. (For this reason, they are described as content-independent or domain-general.) Such mechanisms, by definition, have no pre-existing content built-in to their procedures, they are not designed to construct certain contents more readily than others, and they have no features specialized for processing particular kinds of content. Since these hypothetical mental mechanisms have no content to impart, it follows that all the particulars of what we think and feel derive externally, from the physical and social world. The social world organizes and injects meaning into individual minds, but our universal human psychological architecture has no distinctive structure that organizes the social world or imbues it with characteristic meanings Cosmides and Tooby (1996).

This 'general purpose' view is challenged by a good deal of accumulated evidence. For example, some very strange things can happen to people's abilities when they have suffered from a stroke. One condition that can occur has been termed prosopagnosia. This is a very specific deficit that involves only our ability to recognise faces. This suggests that, functionally at least, if not also anatomically, this ability has specific 'mechanisms' devoted to it, mechanisms that do not deal with 'objects' other than faces. There are similarly quite specific resulting impairments that follow injuries to the brain at other places in its structure (and you can follow these up with material that summarises brain function, written by Emeritus Professor Robert P. Lehr, at Southern Illinois University).

Another source of evidence comes from clinical syndromes, such as Williams syndrome.  People with Williams syndrome are smart and mentally retarded, gifted and inept at the same time. The argument in this case goes:

  • 1. Some parts of language are preserved in Williams syndrome (e.g., syntax). Other parts are compromised.
  • 2. Some parts of spatial cognition are preserved in Williams syndrome, and others are compromised.
  • 3. Therefore, this is evidence for modularity since otherwise we wouldn't expect brain pathology to affect some mental processes (e.g. syntax) more than others.

[Interestingly, in the light of the discussion about how single genes can affect developmental processes in Lecture 4, Williams syndrome has recently been shown to be genetically-based, most likely at a single-gene location.]

So, the modularity hypothesis claims much the same thing as the old 'science' of phrenology did back in the 1800s:

Phrenologists claimed to have localised a number of psychological abilities and correlated them with bumps on people’s skulls. Many contemporary cognitive psychologists argue in a similar way: that parts of our brains are specialised for particular tasks - our mental abilities are 'modularised' rather than 'general purpose devices'.

This issue of modularity is much less cut-and-dried within cognitive psychology than I might be indicating in this summary. It has been entangled with disputes about innateness. The arguments have gone something like this, and are based on the work of Noam Chomsky. Chomsky points out two fundamental properties of language:

  • First, everyone uses their language creatively, regularly saying and hearing completely new utterances.  As in, 'I gave our dog a pint of Guiness followed by ice-cream for breakfast this morning': probably the first time this statement has ever been made, but it makes sense. So, language isn't built up by learning particular examples of appropriate particular phrases to use in particular situations. Rather, we likely have some 'blueprint' of the ways words can be put together, a set of 'grammatical rules' that construct an infinite number of allowable statements from the vocabulary we have.
  • Second, children develop these grammatical rules from a very young age, without formal tuition, and in a similar way across all of the world's cultures. Additionally, there are a number of (quite good) arguments that, since they rarely hear adults speaking proper grammatical sentences in everyday life, the 'data' that children have to go on in constructing their grammatical plans are insufficiently specified as to allow them to 'learn' the rules. Finally, children master language irrespective of their other psychological abilities, such as those 'measured' by intelligence tests. Therefore, children must come with a built-in, innate plan that is common to any language they might encounter, and this guides how they deal with what they experience, enabling them to construct the grammar of the language used in their particular community. And, this 'plan' is an 'autonomous' one, specific to language and not related to other developing abilities.

Language has thus come to be regarded as 'innate' and 'modularised'. But this way of seeing things has come into our intellectual landscape from a time (granted, a relatively recent time) when our knowledge of how developmental processes work to turn genetic information into physical bodies and mental abilities was even poorer than it is today. Development is a constructive process, so that something might be said to have a genetic component yet not be 'innate'; and some things might turn out to be 'modularised' in the adult, but not in the child - the modules are 'constructed' through the developmental process, rather than coming into being in some fledgling form that just 'matures'; and so on. It is necessary to be much more careful in the way we use words with respect to complex issues such as these than I am being here. But then, I'm only trying to introduce you to these notions. For a more careful view, you should look at Professor Annette Karmiloff-Smith's summary of her book Beyond Modularity.

2. Evolution and Modularity

Let's assume that our mental abilities do have a 'modular' basis. They are a bit like a patchwork quilt.

This way of seeing things is quite well established in evolutionary biology, though it took a bit of time for it to become recognised as more-or-less corresponding with 'the way things are'. Thus, Lamark was familiar with the notion of 'mosaic' evolution in the early 1800's, well before it became part of the mainstream of biological thought following Sir Gavin de Beer's book Embryos and Ancestors (1954). Prior to this, a fossil specimen such as Archaeopteryx was not seen as representing a form in the evolutionary line between reptiles and birds, since it is a mixture of reptilian and avian features, rather than being in an equal state of transition between the two forms in all its parts. It took a lot of thought to recognise that evolution can work on different bits of organisms at different rates, rather than uniformly across the entire organism.

The fossil at left is called Seymouria. It is from North America, and is thought to be from the Permian period (between 286-248 million years ago!). It is this organism that led to the notion of 'mosaic' evolution when de Beer re-discovered Watson's paper from 1919, where Watson noted that:

The curious way in which the structure of Seymouria is built up of perfectly well developed amphibian characters and equally decisive reptilian characters, those of intermediate type very rare, affords a magnificent example of the way the evolution of the great groups may have taken place (p. 300).

It is only in the past few years that contemporary psychologists have begun to re-adopt this viewpoint with respect to our psychological abilities. Chomsky again provides an example of the reasoning involved:

It is a curious fact about the intellectual history of the past few centuries that physical and mental development have been approached in quite different ways. No one would take seriously the proposal that the human organism learns through experience to have arms rather than wings, or that the basic structure of particular organs results from accidental experience. Rather, it is taken for granted that the physical structure of the organism is genetically determined....

The development of personality, behavior patterns, and cognitive structures in higher organisms has often been approached in a very different way. It is generally assumed that in these domains, the social environment is the dominant factor. The structures of mind that develop over time are taken to be arbitrary and accidental; there is no 'human nature' apart from what develops as a specific historical product....

But human cognitive systems, when seriously investigated, prove to be no less marvellous and intricate than the physical structures that develop in the life of the organism. Why, then, should we not study the acquisition of a cognitive structure such as language more or less as we study some complex bodily organ (1975: 9-11).

Now, taking this metaphor of cognitive abilities as organs, adding to it the notion that these abilities might be modular in their nature, realising that mosaic evolution is the norm . . . Presto!  We can begin to ask the obvious question as to how different bits of our mental 'kit' might have evolved. And we do that in the light of what we know about evolution: if an individual gains an advantage by being able to do something that gives it a better pay-off down the time-track in terms of how many descendants its genes are represented in as compared to anybody else's; and if what gives it that advantage can be specified and hence preserved by, and transmitted through, its genetic code; then - deep breath - that's what will happen.

3. Recapitulation

Think back a few lectures. I outlined some of the ways in which men might differ from women in the way they are attracted to other individuals. It is quite clear that we are not unique amongst the animal kingdom in showing such differences between the sexes. It is remarkable that men and women should be perceptually sensitive to quite small changes in one another's waist-hip ratios. It is even more remarkable that the WHR that men find most attractive in women is significantly different from the WHR women find most attractive in men. It is mind-boggling that these preferences tie in as good indicators of health and 'mate value', and hence would have had high stake value in the evolutionary gamble. And it is almost incomprehensible that these perceptual preferences could conceivably occur on the basis of just a single gene difference between the two sexes. Almost as incomprehensible as the idea that homosexuality and Williams syndrome could be so founded.

Think back to Lecture 2 where we started with the Fraser spiral visual illusion. How the world appears to us is influenced by the abilities we bring to it. Some of our experiences are by-products of the structures evolution has had to work with. No-one would propose that we evolved the ability to see that illusion because it provided an advantage for us to do so. It's clearly an accidental result of the way evolution has tried to deal with a problem that did convey advantages. Similarly, the problems created by aspects of our anatomy are spin-offs from modifying an anatomy that wasn't the best starting point for something that would gain an advantage from walking on two legs instead of four. Some things about us are clearly accidental. But some things are consilient.

Consilience, according to the Oxford English Dictionary, is 'the act of 'jumping together' or agreeing; coincidence, concurrence; said of the accordance of two or more inductions drawn from different groups of phenomena'. The term is cited as having been coined by the English philosopher William Whewell thus:

1840 Philos. Induct. Sc. II 230. Accordingly, the cases in which inductions of facts altogether different have thus jumped together, belong only to the best established theories which the history of science contains. And, as I shall have occasion to refer to this particular feature in their evidence, I will take the liberty of describing it by a particular phrase; and will term it the Consilience of Inductions. 1847 - Hist. Induct. Sc. II 582. Such coincidences, or consiliences . . . are the test of truth.

It seems to me that there is a degree of consilience in this material we have already looked at. And that it goes a good way to providing the ground from which to see some of the things that we do as resulting from our evolutionary history. Now, this is the claim of contemporary evolutionary psychologists: our abilities need to be considered from an evolutionary perspective.

4. Prospectus

At the same time, we don't want to get carried away. First, this way of looking at humans has had a past tendency to have been adopted uncritically, and has been used both to justify excesses of action as well as to excuse the maintenance of unjust practices within the status quo. Second, as Chomsky noted above, 'The development of personality, behavior patterns, and cognitive structures in higher organisms has often been approached in a very different way'. This approach may 'often' have been in error, but that many social scientists can't have been all wrong. So we need to try and figure out what each approach has to offer. And third, there are a lot of 'buts' we can put in about the applicability of the argument to humans, and a deal of evidence we need to take into account.

Two examples of these 'buts':

1: When did the activities that are characteristic of our species arise? There are some, such as the South African paleoanthropologist Philip Tobias, who regard language as being a possible human activity for at least 1.5 million years. There are others who argue for its being a much more recent accomplishment, such as Bill Noble and Iain Davidson at the University of New England at Armidale, New South Wales. Now, if it were an early achievement, we might not want to look for 'human nature' type explanations of how we orient ourselves to salient features of the world. Having language, for example, opens up a whole new set of opportunities for being a successful individual in the evolutionary game. You wouldn't need 'instructions from nature' to pursue certain lines of activity: you could get these consciously from the language resources of your culture. In this scenario, then the 'standard social science model' would look a good starter. But if language only came on the scene relatively recently, then it is more likely that we would have 'inbuilt' tendencies that predisposed us to differentially value events and ways of dealing with them, since that is the way, as we have seen, that the evolutionary system operates. A recent origin provides a deal more time for selection to have refined and channelled the 'given' tendencies of 'human nature'. And thus a recent origin tends to bode poorly for the standard model. So, which is it? The information we need to resolve this question is the subject matter of a later section of these lectures.

2: Beware of presuppositional myths. So, what did humans get up to in the past? There is an amazing amount of cultural imagery floating around as to what 'cave men' or 'neandertals' were like. Hairy, low-browed primitives carrying a club; males dragging women by their ponytails, and going 'ugh'. We even use the word 'neandertal' as a pejorative. It then comes as something of a shock to see the most-informed reconstruction of what a Neandertal family might actually have looked like, as generated by informed forensic reconstructions from fossilized skulls by a research team at the Biomedical Visualization Laboratory

Somewhat different from what you might have anticipated on the basis of our cultural presuppositions, don't you think? But whether this is any nearer the truth than earlier reconstructions, who actually knows? Again, this is why I look at some of the database on human evolution in the next few lectures, for without that information it is not possible to make an informed judgement on any of the issues we are dealing with here.

5. Evolutionary Psychology

I won't spend time here outlining this approach, because it is done better elsewhere.

  • 1: Two names that you will come across whenever you look at material on this topic are John Tooby and Leda Cosmides, who are at the University of California, Santa Barbara. It is their work that has done the most to bring this approach to the attention of contemporary psychology. They offer a primer to the subject, and you should read it for further details.
  • 2: Edward Hagen at UCSB maintains an 'FAQ' on evolutionary psychology
  • 3: There is a recently published Handbook of Evolutionary Psychology, and the editors, Charles Crawford and Dennis Krebs at Simon Fraser University, Canada, provide a good commentary on the issues in their outline of its contents.
  • 4: There is also an introductory outline called Evolutionary psychology for the common person which tries hard, but often fails to deliver anything of substance.
  • 5: Finally, you could try Francis Steen's CogWeb site

6. Machiavellian Intelligence

'I suspect that you wonder whether I realize how hard it is for you to be sure whether you understand whether I mean to be saying that you can recognize that I can believe you want me to explain that most of us can keep track of only about five or six orders [of intensionality]' . Daniel Dennett (1983).

Machiavelli's book The Prince, published in 1532, is a classic of political strategy. It offers advice to a prince or politician as to how to attain power, through deceit, forming coalitions, keeping in good favour with patrons, and the like. Much current research portrays primates, particularly the great apes, as Machiavellians in their own right (see, for example, Byrne and Whiten, 1988, who introduced this term to the field). They are portrayed as social tacticians who have a canny knowledge of each of their companions and the networks of social relations amongst them. They are flexible and often fickle in the cooperative alliances they make, and thus manage to outmanoeuvre others in the pursuit of resources. And they have a wide repertoire of tricks for social manipulation, ranging from deceit to reciprocal altruism.

This way of looking at primates was independently outlined by Alison Jolly (1966) and Nick Humphrey (1976). One of the problems that primates posed was that they display a baffling mix of intelligence and stupidity. If confronted with problems by psychologists in the laboratory, then they appeared to be very intelligent. But these problems do not confront primates in their natural environment, so why are they so intelligent?

'It has been repeatedly demonstrated in the artificial situations of the psychological laboratory that anthropoid apes possess impressive powers of creative reasoning, yet these feats of intelligence seem simply not to have any parallels in the behaviour of the same animals in their natural environment. I have yet to hear of an example from the field of a chimpanzee ... using his full capacity for inferential reasoning in the solution of a biologically relevant practical problem. Someone may retort that if an ethologist had kept watch on Einstein through a pair of field glasses he might well have come to the conclusion that Einstein too had a hum-drum mind. But that is just the point: Einstein, like the chimpanzees, displayed his genius at rare times in 'artificial' situations - he did not use it, for he did not need to use it, in the common world of practical affairs' (Humphrey, 1976: 307).

Jolly's and Humphries' key hypothesis was that primate intelligence evolved as an adaptive response to the most important things in any primate’s environment: other primates.

It is no accident therefore that men, who of all the primates show the longest period of dependence, the most complex kinship structures, and the widest overlap of generations within society, should be more intelligent than chimpanzees, and chimpanzees for the same reasons more intelligent than cercopithecids.
Once a society has reached a certain level of complexity, then new internal pressures must arise which act to increase its complexity further. For, in a society of the kind outlined, an animal's intellectual 'adversaries' are members of his own breeding community. If intellectual prowess is correlated with social success, and if social success means high biological fitness, then any heritable trait which increases the ability of an individual to outwit his fellows will soon spread through the gene pool. And in these circumstances there can be no going back: an evolutionary 'ratchet' has been set up, acting like a self-winding watch to increase the general intellectual standing of the species'
(Humphrey, 1976: 310-1).

Previously, a great deal of emphasis had been placed on the development of technology, as evidenced by tools, as the factor selecting for increased 'intelligence'. Links have been proposed between tool-use and the origins of language. These kinds of explanations have always been couched in terms of how these developments would provide a selective advantage to their possessors because of the increased control over environmental resources that they make possible. So it is a quite dramatic shift to see the social world created by animals themselves being put forward as the candidate for driving human evolution. And that might raise in your mind a 'big' question. Think back to the issue about our 'presuppositions' noted above, and how they can unconsciously influence our expectations of what something will be like.

Could it be the same here? That the emphasis on technology came about not directly from the evidence itself, but from the zeitgeist of the times in which the evidence was being interpreted and turned into a narrative account of the human origins story?

At least two lines of research align themselves with this evolutionary perspective. The first is generally known as 'Theory of Mind' research, and this pursues questions in both developmental and comparative psychology as to what children and other animals know about other minds. For example, when do young children come to understand that other people have beliefs about the world, and that these can on occasion be wrong? When might a child be able to understand that if you hide an object in full view of them and their mother, and then move the object to another place while mother is out of the room, that their mother no longer knows where the object really is, but still believes it was where they originally saw it being hidden? When can children use the information that Paul knows something that Jane doesn't to predict what Paul and Jane will do in certain situations? When can they keep track of social situations in which Paul thinks that Jane believes that he wonders whether she thinks he is lying? And how many of these chains of inference can an ape cope with? Such questions have led, over the past decade, to some of the most sophisticated experimental work on human abilities ever carried out.

The second area concerns whether our problem-solving abilities are general or specific. We will deal with this issue in more detail in class. Briefly, Wason (1966) presented the following problem (selection task) to his participants:

Among four cards, "E," "F," "4," "7," choose only those cards that must be turned over to see if a rule, "A card with a vowel on one side has an even number on the other side," holds for these cards.

He found that only a small portion of participants (typically, less than 10%) made the logically correct answer (i.e., "E" and "7"). However, if one sticks with the same logical structure but makes the problem one about cheating, asking 'which cards do you have to turn over to find out whether someone has cheated', then practically everyone gets the right answer.

Try these problems on some friends, and see if they find one easier than the other.

'You have just taken a new job as a school secretary. You think the last secretary has made some mistakes in the filing system. Childrens' records should be marked with a letter on one side and a number on the other. The standard 'Wason rule' applies to the filing system, that is a child's record must be coded so that "A card with a vowel on one side has an even number on the other side". You are confronted with four record cards you have pulled out of the file, which show "E," "F," "4," "7," Which are the only cards you have to turn over to see if they have been correctly coded?'

Answer: 'E' and '7'

'You are the member of a hunting party in New Guinea, and you lose all your equipment and supplies while crossing a river. You and your partners get lost and very hungry when you meet a man who says his headman might well feed you, so you follow him. Unfortunately, you discover his headman is 'Big Willy', the leader of a bunch of cut-throats, which you should have realised, since he makes all his tribe have the word 'Big Willy' tatooed on their foreheads. Big Willy and his men are outcasts, and feared by everyone. Big Willy tells you that 'yes' he will feed you and your partners, but only in the morning, and if you agree to his tatooing 'Big Willy' on your forehead this evening.

In the morning, you are faced with the following cards that have information about whether a partner got a tatoo on one and whether he got fed this morning on the other. You can see four cards. They say:

  • 'Got a tatoo'
  • 'Didn't get a tatoo'
  • 'Got fed'
  • 'Didn't get fed'

Which cards do you need to turn over to see if any of your partners got cheated by Big Willy?

Do people find one of these easier than the other?

The claim from evolutionary psychology is that our problem-solving abilities are not general ones, but are specifically tuned to deal efficiently with just those problems that evolution would have set as important to us. In a similar vein, evolution has equipped us with specialized modules that recognise faces as opposed to other objects, and perceptual biases that have us prefer some waist-hip ratios over others, etc.

Yerkes Regional Primate Research Center

The Newsroom

August 30, 1996

The Evolution of Morality

Is human nature fundamentally selfish or fundamentally noble? It is both, claims Dr. Frans de Waal, Research Professor of Psychobiology at Yerkes Regional Primate Research Center and Professor of Psychology at Emory University. Through his work with primates, Dr. de Waal illustrates the concept that morality is not merely man's cultural invention, but a product of millions of years of evolution.

Dr. de Waal describes his observations in his most recent book, Good Natured: Origins of Right and Wrong in Humans and Other Animals. Many of the roots of human behavior can be traced to our primate heritage, says Dr. de Waal, a Dutch-born zoologist and ethologist. He suggests that basic ethical behavior -- helping one who is hurt, feeding one who is hungry -- is not unique to humans. Animals are compelled, perhaps by their own code of ethics, to respond to social rules, to help each other, to share food and resolve conflict to mutual satisfaction. Thus, the natural world involves not merely survival of the fittest -- but survival through cooperation and mutual assistance.

In fact, de Waal says, natural selection has produced some highly cooperative species. He cites examples: a female chimpanzee shares food with a juvenile not related to her; a herd of African elephants tries to revive a young female dying from a poacher's bullet, then spreads earth and branches over the body before leaving it; a group of dolphins supports an injured companion at the water's surface to prevent it from drowning. Dr. de Waal sees in this cooperative behavior the evolutionary roots of human moral systems -- the need for social order, sympathy, empathy, justice and peace.

"What is interesting to contemplate is, when animals help another, do they understand exactly what the situation is and then adjust their help to whatever the other individual needs? I do think chimpanzees have the capacity for empathy, for understanding what some else feels or needs," says Dr. de Waal.

Dr. de Waal's insights bring us face to face with the profound paradox that genetic self-advancement at the expense of others -- which is the basic thrust of evolution -- has given rise to remarkable capacities for caring and sympathy. "Just as in animals," says de Waal, "for humans, making peace is as natural as making war." This notion creates a more complex picture of the evolution of morality, but an infinitely more inspiring one.

Dr. de Waal has also authored numerous scientific papers and two other award-winning books on primate behavior, Chimpanzee Politics and Peacemaking Among Primates.

For more information:

Kate Egan, Public Affairs Office, 404-727-7709, [email protected]


Chomsky, N. (1975) Reflections on language. New York: Pantheon

Dennett, D. (1983) Intentional systems in cognitive ethology: the 'Panglossian paradigm' defended. Behavioral and Brain Sciences 6: 343-90.

Humphrey, N. (1976) The social function of intellect. In P.P.G. Bateson and R.A. Hinde (Eds) Growing points in ethology. Cambridge: Cambridge University Press.

Jolly, A. (1966) Lemur social behavior and primate intelligence. Science 153: 501-6.

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