Evolutionary Psychology

A Beginner's Guide

Robin Dunbar, John Lycett, Louise Barrett

• Publisher: Oneworld Publications
• Year: 2005
• ISBN:
  9781780740195
• Topic: Biowissenschaften
• Subtopic: Entwicklung

Evolutionary Psychology: A Beginner's Guide is a uniquely accessible yet comprehensive guide to the study of the effects of evolutionary theory on human behaviour. Written specifically for the general reader, and for entry-level students, it covers all the most important elements of this interdisciplinary subject, from the role of evolution in our selection of partner, to the influence of genetics on parenting. The book draws widely on examples, case studies and background facts to convey a substantial amount of information, and is authored by the UK's leading experts in the field, from the only dedicated research and teaching institute.

1

Why do we need evolution?

When Charles Darwin launched his book On the Origin of Species on an unsuspecting Victorian audience in 1859, he triggered an intellectual shock wave that continues to send ripples around the world. One implication to which his book drew attention (though it was not one of Darwin’s own insights) was the fact that we humans are very much members of the animal kingdom. We are members of the order Primates, the group that contains all the monkey and ape species. In the past decade or so, we have gone one step further than any of Darwin’s contemporaries ever imagined in this respect. Genetic evidence has convincingly shown that, far from being a distant cousin of the monkeys and apes, we are very firmly embedded in the ape family as the sister species of the chimpanzees.

Darwin and the mind

While Darwin’s theory of natural selection has been truly revolutionary in the history of science, it was not Darwin’s ideas on how species are formed that were to achieve such prominence in the long run. Looking back on the 150 years of intellectual history since The Origin was published, we can see a growing importance for his later books The Descent of Man (in which he explored sexual selection and reproductive behaviour) and The Expression of the Emotions in Man and Animals (in which he tackled the nascent field of psychology). Darwin’s ventures into the field of behaviour were much underrated – indeed, his theory of sexual selection, with its emphasis on the processes of mate choice, did not come to occupy the position of importance that it now does within evolutionary biology until more than a century after The Descent of Man was published. And in many ways, we are still absorbing the lessons of his work on emotions. But both books were extraordinarily prescient, in that Darwin put his finger on issues that have since come to be seen as fundamental to our understanding of human behaviour and the mind that underpins it.

The past three decades have witnessed an extraordinary explosion in our understanding of animal behaviour and its evolutionary components. This explosion has involved both the development of a very sophisticated body of theory, much of it underpinned by mathematical models and a volume of observational and experimental research on animal behaviour that would have excited the grand old man beyond measure. For it was Darwin’s genius to bring together a powerful combination of acute theoretical insight with empirical tests using data from a wide range of species. Known as the comparative method, this has remained the methodological cornerstone of the evolutionary approach to this day.

While the study of non-human animals progressed apace from the 1970s, the extension of these ideas to human behaviour and psychology had to wait for the better part of another two decades before its own explosive take-off. In part this reflected a nervousness on the part of biologists towards dabbling in things human, but also the distrust in which social scientists had held evolutionary and biological ideas since the early 1900s. However, from the late 1980s onwards, evolutionary ideas began to be applied in earnest to the study of human behaviour and the human mind. This field is so new that its findings are only available in the more specialized journals. This book is an attempt to draw together some of the more salient findings from this research in a form accessible to the general reader.

Before we begin, we need to make clear what an evolutionary approach to human behaviour does – and does not – entail. The value of the evolutionary approach is that it provides us with a sound theoretical framework which enables us to generate a set of precise hypotheses concerning behavioural responses and psychological mechanisms and subject them to rigorous tests using data from the real world.

We can ask questions about the history and development of a trait both over geological time (its phylogenetic cause) and within the lifetime of an individual (its ontogenetic cause), determine how a behaviour enhances survival and reproduction (its functional or ultimate cause) and identify the factors that trigger a particular behavioural response to occur (its motivational or proximate cause). Niko Tinbergen, who won the Nobel Prize in 1973 for his work on animal behaviour, pointed out that each of these questions, while appearing very different at face value, is really just a different way of asking the same question – why does an animal display a particular trait? – with the answer pitched at different levels of evolutionary explanation. Each of these four senses of ‘why’ is important, and each can be equally informative. But it is very important not to confuse these levels of explanation by providing, for example, a proximate level answer to a question that asks about the function of a behaviour. Partitioning the kinds of questions we can ask in this way is now known, in his honour, as Tinbergen’s Four Whys.

By formulating our questions carefully and making sure our answers are pitched at the appropriate level of explanation, we can identify whether behaviours are adaptations produced by the process of natural selection, whether they are by-products of selection for other traits, whether they were initially selected for other purposes but have been co-opted by evolution to serve a new role (sometimes known as ‘exaptations’) or whether they serve no evolutionary function at all. In other words, the aim of the evolutionary approach is to understand the advantages that traits confer on individual organisms, how these interact with other traits (for example, how having a large brain means that it takes longer for an animal to reach sexual maturity) and how a species’ evolutionary history constrains the range of adaptations that are possible.

Genetic determinism: the evolutionary red herring

What an evolutionary approach does not involve, however, is any notion that all behaviour is genetically determined and that our biology is our destiny. This issue continues to exercise many people – mainly social scientists, but some biologists have also become surprisingly consumed by it. Much of the criticism levelled at evolutionary approaches to human behaviour seems to rest on the belief that an evolutionary explanation of behaviour necessarily implies that behaviour must be genetically determined. At face value, this may seem a reasonable conclusion to draw. After all, most discussions concerning the evolution of behaviour are explicitly couched in terms of ‘the gene for a behaviour’; moreover, the success of a given behaviour is explicitly measured in terms of its fitness (a term from population genetics that refers to the relative number of copies of a particular gene that an individual contributes to future generations).

Given this, it might indeed seem to follow that any discussion of evolution must mean genetic evolution. The logic of this argument would appear to be inescapable. But the fundamental question we have to ask is: does it have anything to do with the evolutionary study of behaviour? The short answer is no. There is a world of difference between claiming that we can provide an evolutionary explanation for behaviour and claiming that we are offering an explanation in terms of the genetic determination of behaviour. This is so for two reasons. First, no known species of organism (with the possible exception of single-celled creatures like viruses and bacteria) shows genetically determined behaviour in this way. Behaviour is simply too complex to be determined by single genes. More importantly, if a behaviour truly were genetically determined, it would mean that the behaviour always developed in exactly the same way in each individual and that environmental influences exerted no influence whatsoever. This would result in behaviour that, by necessity, would be completely inflexible: the organism would always behave in the same way, irrespective of the circumstances. Genetic determinism on this scale is an excellent recipe for the rapid extinction of the species in question; it is not a particularly helpful foundation on which to base an effective interaction with a complex, constantly changing world.

Vertebrates evolved large brains precisely to allow them to adjust their behaviour to suit the circumstances in which they happened to find themselves on a moment-by-moment basis. The genes that code for the brain have been selected expressly to enable the organism to escape from a genetically driven existence. Ironically, given the fears of genetic determinism and the loss of ‘free will’, it is our genes that free us from these deterministic constraints.

An evolutionary approach to understanding behaviour is most definitely not about identifying a single causal link between genes and behaviour. This misunderstanding often arises because an evolutionary approach does require some genes in the system, so convention enjoins us to identify some arbitrary notional gene as the focus for our thinking. The genes in evolutionary explanations are no more than a device for keeping our thinking straight. This does not necessarily mean that there are no specific genes involved, of course, but that is a question that has a purely empirical answer, which must be provided by developmental biologists, not by evolutionary psychologists.

Second, the evolutionary study of behaviour is not actually about the genes that determine behaviour, even in the weak sense that there must always be some genetic constraints on the capacity to behave at all. The point is that an evolutionary approach is concerned with a strategic analysis of behaviour: why does the individual behave in this way, in the sense of ‘what purpose does it serve for the individual?’ A strategic view makes no specific assumptions about what determines behaviour, it simply assumes that an individual’s choice of behavioural strategy is guided by evolutionary considerations (that is, maximising its contribution to the species’ gene pool in future generations).

Darwin, genes and behaviour

The evolutionary approach to the study of behaviour raises four separate points that need to be clarified:

First, such explanations sound as though (and have certainly been interpreted as implying that) animals make explicitly conscious decisions about their genetic future. No organism can do that, not even humans. Rather, this kind of explanation makes no assumptions at all about how such decisions are made: it could be entirely genetically driven and unthinking, but it could equally be entirely learned and deliberate, or it could be anywhere in between. Which of these possibilities is correct is an interesting empirical question but the answer does not have any implications for whether animals are behaving strategically, or, indeed, whether evolutionary considerations have had a hand in their decisions.

Second, while organisms which behave in a way that increases the number of their descendants in future generations can be considered to have higher fitness, this does not mean that the actual goal of that behaviour is the maximization of fitness. The goal of an Ache hunter from Patagonia may be, on one occasion, to hunt and kill a tapir, or on another to marry off one of his children and dance at the wedding. The link to fitness can occur very far down the line and there is no reason to expect people, any more than other animals, to show behaviours that are overtly designed to increase their fitness (the number of descendents they leave), even though that is their eventual consequence. The achievement of a much more proximate goal can have fitness-enhancing effects, but there need be no direct link between the two. This extended link, via a series of intermediate proximate goals, between behaviour and its ultimate fitness consequences, allows us to explore organisms’ behavioural decisions by focusing on immediate short-term consequences such as maximizing energy intake (in the case of hunters) or maximizing the number of offspring sired (in the case of mating strategies), while assuming that successful solutions to these proximate problems will eventually carry through into higher fitness. In behavioural ecology, this is known as the phenotypic gambit.

Third, the assumption that organisms are designed to behave in such a way as to maximise their genetic fitness is a heuristic device rather than a presumption of fact: it provides us with very precise predictions, which can be subjected to clear empirical tests. In contrast, the criticism of genetic determinism is explicitly focused on the machinery that permits behaviour to occur – in effect, what enables the hardware to be produced. This is a how question and is clearly entirely different from asking why behaviour occurs.

Fourth, evolutionary explanations are statistical. Perhaps the commonest attempt to counter an evolutionary explanation is: ‘Well, my children don’t do that!’ A specific example, however, cannot negate a statistical rule. To disprove the claim, you need to show that on average children do not behave in this way. The statistical nature of evolutionary explanations is important – indeed crucial – because evolutionary change cannot happen if everyone behaves in the same way. Organisms have to constantly test their environment, whether this be physical or social, in order to determine whether they are behaving in an evolutionarily optimal fashion. Some individuals will inevitably get it wrong. But, now and again, this trial and error learning will yield a novel solution that is better than all the others. Gradually, this solution will spread through the population, as those who have it (or adopt it) reproduce more successfully. But even so, that solution will never be adopted by everyone in the population: individuals will continue to try out new ones, and some will continue to get it wrong.

In short, the dispute confuses two quite different kinds of question that one might ask of the world: why something occurs or how it occurs. The confusion probably arises because the word gene is used in both kinds of explanation. One focuses on genes as causes of behaviour (or the capacity to behave), the other focuses on genes as consequences of behaviour (that is to say, the effect that behaving in a particular way has on the genetic make-up of the next generation). Although evolutionary biologists keep these two meanings clearly separated in their minds, those who are less familiar with this approach often confuse them.

Although these two processes are necessarily linked, it does not follow that, in any particular case, the same set of genes is both cause and consequence. In large-brained organisms like mammals and birds, this evolutionary loop is often closed by the brain. Consider an organism that has a large brain, which enables it to adopt flexible behavioural strategies. This allows it to fine-tune its behaviour, in the light of current circumstances, so as to maximize the number of matings it achieves, thereby maximizing the number of offspring it contributes to the next generation. What is passed on from generation to generation and so makes both evolution and the behaviour possible, are the genes for a big brain. But the genes that code for the brain do not determine the behaviour (mating) that the brain gives rise to; rather, they merely determine the capacity to make flexible decisions that are well tuned to local circumstances.

Finally, it is worth remembering that when Darwin first formulated his theory of natural selection, he had no knowledge of genes at all. In fact, his new theory was much criticized for containing what many regarded as a very inadequate mechanism of inheritance. Darwin’s theory of evolution by natural selection was only rescued from the growing obscurity into which it fell after his death by the rediscovery of Mendel’s laws of inheritance.

Although Gregor Mendel, abbot of the monastery at Brno (in what is now the Czech Republic), was developing his laws of inheritance at the same time as Darwin was developing his grand theory, his ideas were not widely appreciated outside his home town (Darwin, who had a copy of Mendel’s paper, certainly failed to understand their significance). Remarkably, this key which unlocked Darwin’s grand theory remained overlooked in the dusty volumes of obscure libraries for more than half a century until it was rediscovered by geneticists in the early 1900s. The result was what is known today as the new synthesis – the amalgamation of Darwin’s theory of evolution by natural selection and Mendel’s laws of inheritance into a single unified theory.

In any case, Mendel didn’t know about genes either! For both Darwin and Mendel, inheritance was all about ‘fidelity of copying’ between parents and offspring. This has one very important implication: evolutionary processes do not have to depend on genes. Anything that causes a correlation between parents and offspring has the capacity to be a Darwinian process. The things that an organism learns in its lifetime and passes on to its offspring can also undergo a process of natural selection. It is entirely possible and equally evolutionary, for non-genetic inheritance to take place and for such non-genetic resources to be selected over time. Cultural processes can therefore have very important evolutionary effects and this is especially true of our own evolution. In other words, understanding human behaviour from an evolutionary perspective may not require the involvement of any genes at all.

Disentangling the web

In this book we will rely heavily on a strategic perspective. At each step, we will ask how humans behave in some particular respect. We will then go on to ask what cognitive and physiological mechanisms underpin this behaviour. Where we can, we will ask about the developmental processes involved, in an attempt to address the question of how genetic inheritance and learning interact to bring such behaviour about (however, what we can do in this respect is presently severely limited by our almost total ignorance of the processes involved). And, finally, in a few cases, we will ask questions about the evolutionary history of a particular phenomenon (although the number of cases where we really can say anything useful about this is even fewer). For the moment, our concern will mainly be to raise questions about the processes involved and point to possible ways ahead.

Evolutionary psychology has often been seen as an alternative to more conventional approaches in psychology, the equivalent of developmental psychology, cognitive psychology or social psychology. That, however, is to misunderstand what the evolutionary approach is all about. In biology, the evolutionary approach provides a unifying framework that allows different subdisciplines (behaviour, ecology, physiology, genetics, anatomy, biochemistry, etc.) to talk to each other. In effect, Tinbergen’s Four Whys spell out how the various subdisciplines are related and allow them to interact without confusing the issues or getting into pointless disputes. In our view, evolutionary psychology supplies the same service for psychology, creating a theore...