Evolution

A. Principles of evolution

This section further develops the basis of the evolutionary and functional types of explanation.

1. Functional explanation, fitness and natural selection

In the present context, ‘function’ is used (in the etho-logical sense) in terms of reproductive success. The term fitness refers to the potential of an animal to reproduce successfully. Fitness is a measure of the animal’s ability to pass on its genes, in terms of the number of viable reproducing offspring that arise. Thus, types of behaviour that increase fitness are favoured in evolution by natural selection. (This sense of fitness should not be confused with the reference simply to bodily health.)

Closely related to the functional level of explanation is the notion of adaptation (Chapter 1). A physical feature or behaviour is adapted to an environment in that it has been tested for its suitability to that environment. Those individuals that provide the best fit survive and pass on genes. However, there are some complications to this account (Buss et al., 1998; Gould and Vrba, 1982), as follows.

A trait (‘characteristic’) that evolved by means of natural selection might no longer serve a useful function in the present environment. A good example of this is our excessive liking for sweet substances, which is associated with contemporary obesity (Power and Schulkin, 2009). It is assumed that, in an early environment, our ancestors were more physically active and an attraction to rare ripe fruits would have been of enormous adaptive value. They provide energy in an environment where the supply of food is uncertain. However, we now have a relatively inactive lifestyle and an abundance of refined sweet items alongside the supermarket checkout, and so the same characteristic leads us into dangerous temptation.

Also, something might now be observed to serve a useful function but it evolved in the service of some different function. Noses and ears did not evolve because of their advantage as mechanical supports to those who wear spectacles! A capacity to read and write is doubtless advantageous in our society and there are identifiable brain mechanisms that underlie it. However, seen in evolutionary time, a written language and reading emerged recently. Reading and writing attach themselves to brain mechanisms that evolved much earlier than the appearance of written language. The combination of reading/writing and its biological bases has not had time yet to be tested by natural selection.

Of course, we do not have access to the environment of an animal’s ancestors. Life on Earth has been around for a very long time! However, psychologists have insight based on extrapolation from the present (Tooby and Cosmides, 1990). They can be certain that (except in, say, the depths of the ocean) the environment was illuminated in an approximately 24 hour cycle of light–dark. They know about the magnitude of gravity that birds had to overcome in flying and the saltiness of seawater. Our species was probably subject to parasites. Psychologists can try to interpret the pressures for survival of present species’ ancestors in terms of what they know about constant features of the environment and then speculate about different and past environments.

What can we expect adaptation to achieve? Suppose that an animal detects a predator and, predictably, responds by fleeing rather than carrying on with what it was doing. It gets ambushed by an unseen fellow ‘gang-member’ predator and is then eaten by both predators. This might not seem beneficial to the fleeing animal’s reproductive success! Natural selection cannot arrive at the perfect solution. It cannot account for every instance of behaviour but can merely favour certain ranges of options (Tooby and Cosmides, 1990). Of course, animals cannot inherit genes that tell them what to do under every different circumstance encountered. Rather, genes help to organize nervous systems that have certain general tendencies. Scientists assume that, in the ancestral history of the animal just described, a nervous system that played a role in the reaction of fleeing was of overall advantage, compared, say, with carrying on regardless. The strategy worked more often than it failed.

A principle of ethology (the study of the behaviour of animals under natural conditions) is that no behaviour can bring pure gain. There is a mixture of costs and benefits involved in anything that an animal does, as is argued next.

2. Costs and benefits

The principle can be illustrated as follows. When a jungle fowl is incubating eggs, it loses weight by staying on its nest and not eating (Hogan, 1980). How could this increase its fitness? Suppose that the mother leaves the eggs to obtain food. This increases the chances of the eggs cooling or being eaten by predators. Thus, in terms of the chances of passing on genes, there is a potential cost attached to leaving the eggs. There is also a potential benefit of doing so, i.e. to gain food and hence replenish reserves and streng then the body. However, it appears that over evolutionary history, the cost of leaving the eggs has outweighed the benefit, and so there is a net advantage in staying. Investigators assume that the ancestors of jungle fowl were confronted with the problem of predation and cooling of eggs. Genes that coded for staying were placed at an advantage. However, rather as with fleeing and getting captured, evolution cannot guarantee that sitting on eggs will work in every instance. Both the sitting bird and its eggs might get eaten at the same time. It is merely that a strategy of staying has, over countless generations, been more successful than not, relative to the alternative of regularly leaving the nest. The example illustrates a number of issues associated with relating causation and function:

1              In terms of homeostasis, it is not to the female’s individual bodily advantage to stay on the eggs. Individual survival of her body might be best served by leaving them, to obtain food. However, the chances of passing on her genes are increased by incubation. She might have several eggs, each containing copies of her genes.

2              We should not suppose that the jungle fowl has knowledge in terms of function, i.e. she has no conscious intention to pass on genes (or even unconscious intention!). She just acts in such a way that this is achieved. Among her ancestors, jungle fowl that behaved in this way have been successful and their descendants are around today. Their genes have been favoured by natural selection. A gene coding for ‘not incubating’ has tended to perish.

3              Related to 2, in asking how behaviour is organized, we should not confuse causal and functional explanations. Claims that the bird acts this way because she needs to reproduce are misleading and can lead to the implicit assumption that she has conscious intentions. Birds do not read Darwin! On a causal level, in the brain there is an inhibitory link from incubation to feeding. Natural selection will favour such a mechanism for restraining feeding.

4              It is often argued that natural selection acts on individuals via their genes rather than species as a whole, i.e. it acts to the relative advantage or disadvantage of passing on the genes of individuals within a given population. In this sense, the whole process is sometimes described as ‘selfish’, as in the term self-ish gene (Dawkins, 1976). However, although genes are not selected to act for the good of the species as a whole, genes that bias in favour of acting for the immediate social group could prove advantageous (Wilson and Csikszentmihalyi, 2007).

Having described principles of function and evolution, in the next section we focus on the processes that control behaviour, involving the causal and developmental/learning types of explanation. In doing so, we look for links with functional and evolutionary considerations.

B. Evolutionary psychology

1. General principles

A development of evolutionary thought has assumed great importance in suggesting explanations of human mind and behaviour. It is termed evolutionary psychology (EP) and its followers search for integrative principles linking evolution and psychology, in terms mainly of function (Barkow et al., 1992). Evolutionary psychologists argue that, in order to understand mind and behaviour, we need to look way back to consider the environment in which we evolved and the nature of the demands that it imposed on our early ancestors (Workman and Reader, 2008).

EP employs the metaphor of design. For instance, a bird’s wing looks as ifa designer planned it with flight in mind. Similarly, it is as if our brains were designed so that behaviour fitted our early evolutionary environment. The environment in which we evolved was, of course, very different from that of modern London or Oslo. Our hunter-gatherer ancestors lived very different lives in that early environment, compared with ourselves. Yet we are still adapted for life in this older environment and our nervous systems were, in effect, ‘designed’ for solving the problems of life there. EP argues that it would be absurd to try to explain the workings of a car or a radio, or a heart or lung, without knowing what it was designed to do. By analogy, they argue that psychology also needs an evolutionary ‘design’ perspective. In this way, EP claims to have a unifying theoretical approach for all psychologists, including those concerned with causation and the brain.

Viewed in these terms, we can make sense of fea-tures of behaviour that otherwise might appear bizarre, e.g. our contemporary love of sweet foods even in the midst of an epidemic of diabetes, obesity and dental decay. Our behaviour reflects what was ‘designed’ for a life where there was not an abundance of sugars. For another example discussed by evolutionary psychology, why do symmetrical faces tend to be more attractive than asymmetrical ones (Perrett et al., 1999)? One possible answer is that the symmetrical face is indicative of a younger age and a healthier developmental history. Thus, being attracted to such a stimulus would increase the chances of successful mating and is a factor that would be favoured by natural selection.

EP assumes that many features of human social life (e.g. worship), which might have been thought to be explained purely by cultural influences, are really to be explained at least in part in evolutionary terms (Workman and Reader, 2008). This is sometimes expressed uncritically by those who either promote or condemn a simple EP, as ‘a gene for adultery’ or ‘a gene for religion’ (note the singular ‘a’). However, EP does not rest or fall on an assumption of single-gene effects. A combination of genes might give a bias towards, say, religious worship, since, by so doing, this combination has been placed at an advantage. Indeed, religion might still confer some adaptive advantages: as the cliché would have it ‘families who pray together stay together’.

An immediate and well-worn qualification needs repeating: worship cannot literally be ‘in the genes’. However, given certain genes, together with their social and learning contexts, worship might tend to emerge. By the same token, neither, for example, could physical height be determined simply by genes. Genes are a factor but for height to emerge also requires an appropriate environmental input, e.g. adequate food.

Such discussion has some important social messages. One of the reasons why EP is controversial is that it might at first seem to lend itself to rigid determinism. If something is ‘in the genes’, there appears to be little we can do about it. However, even if certain genes do exert a tendency in favour of, say, adultery, they represent only one contributory factor. The ‘favoured’ outcome is not necessarily inevitable.

The aspect of EP that has most fired the popular imagi-nation and controversy is what it says about differences between the sexes (Workman and Reader, 2008). One point needs to be emphasized here. Though evolutionary theory might give insights into how behaviour has emerged in evolution, it cannot prescribe what humans shoulddo morally. Such an unwarranted extrapolation is termed the ‘naturalistic fallacy’, and is a reason that doubtless turns some against evolutionary approaches.

2. Sex differences

Why do males appear to make more use of prostitutes and pornography and show a wish for greater indiscriminate promiscuity than do females? One might suppose that this reflects cultural norms and prohibitions ingrained in our institutions, i.e. ‘social role theory’ (see Archer, 1996). Change society, give enough time, and behaviour might change correspondingly. On the contrary, EP would suggest that such differences between the sexes reflect evolutionary history and different strategies of mating.

The optimal strategy for a human male (as with many species) to pass on his genes is different from that of a female. An instant and relatively indiscriminate sexual motivation and arousal, accompanied by promiscuity, might be to the advantage of the male since it maximizes his reproductive chances. There is relatively little to lose. The emphasis is on ‘relatively’ since, as always, there is not zero cost. For example, diseases can be caught and, since mating tends to focus the mind, genetic perpetuation might be rudely halted by an approaching tiger or jealous partner. However, for the female there is relatively much to lose. Some female inhibition and reserve (‘coyness’) might be to her genetic advantage, since in this way she can patiently wait to select the optimal male with whom to tie up her reproductive capacity for nine months or so and provide support.

Of course, few if any males visit prostitutes with the intention of passing on genes but no one is supposing that conscious intentions have had much to do with the evolution of sexuality. It is simply claimed that genes tend to code for those strategies that in general have served their own ‘selfish’ interests. In evolutionary history, a combination of genes that tended to promote male promiscuity via sexual motivational processes has been successful. Not all males are promiscuous. EP does not suggest that they should be, just as it does not suggest that all females should show coyness and fidelity. Genes give rise to tendencies not instructions carved in stone. It is simply that one can see a biological rationale in there being a difference between the sexes in this direction.

There is a point here many people misunderstand. Throughout evolution, rather than favouring desire for obtaining children as such, natural selection favoured sexual motivation. Of course, in the absence of a reliable technology of contraception, sexual motivation tends rather frequently to lead to children! This is not to deny that these days some people do desire to produce children as such but sexual desire was doubtless the driver in evolution. A casual glance at society today might suggest that this particular driver has lost none of its momentum over the course of human evolution.

While not denying the possibility that genetic differences might exert different degrees of tendency, explanations need to be framed in the broad gene–environment context discussed earlier. Biology is revealed within a cultural matrix (Barkow et al., 1992).

3. Jealousy

EP makes testable predictions concerning sexual jealousy. What is the cost to an individual’s chances of passing on his or her genes if the partner exhibits infidelity? The cost to a male partner could be large since it might be that his female partner produces offspring bearing another male’s genes. Hence, the male partner misses his own opportunity of genetic transmission. The male partner could even unwittingly help with bringing up someone else’s offspring. Thus, male sexual jealousy might involve a strong imperative against the sexual infidelity of his mate.

In terms of the female’s genetic perpetuation, the cost of a partner’s infidelity might seem to be much less. The female can at least be sure that the offspring she produces are in part genetically hers. A male can recover his sexual potency relatively quickly, and with it, his capacity to contribute genes to reproduction with the female partner. However, there is a threat to the partner from other females, which comes from the risk of being abandoned. The danger of this might be signalled by the male showing an abnormally large emotional interest in the well being of another female, i.e. warmth and empathy. If that were to happen, the female might be put at a disadvantage in raising offspring. Therefore, one might expect some asymmetry in the trigger stimuli to jealousy, with males triggered more strongly by sexual infidelity and females by ‘emotional infidelity’.

Working in the USA, Buss et al. (1992) invited people to imagine various scenarios and estimate the magnitude of the negative feelings that were evoked. These scenarios were of your mate (i) having sexual intercourse with another or (ii) forming a deep emotional attachment to another. Eighty-five per cent of the women found the second to arouse more negative emotions, whereas 60% of the males found the first to do so. EP predicts a difference in this direction. A similar effect was found in the Netherlands, a country with a tradition of egalitarianism and more progressive culture.

Some argue that, rather than reflecting evolved differences, such differences are due to different perceptions of the respective roles of men and women in our culture. For example, society suggests that in women, sexual infidelity is not likely to occur without emotional infidelity – the so-called ‘double shot’. By contrast, male sexual infidelity can be dismissed as being without emotional attachment (DeSteno and Salovey, 1996; Harris and Christenfeld, 1996). However, although not denying a cultural/cognitive factor, the EP researchers suggested that these different perceptions of sex roles are themselves to be understood in biological terms and directly capture the biological difference (Buss et al., 1996). Cultural trans-mission of information might be expected to reflect and reinforce genetically determined differences.

4. Critiques of evolutionary psychology

Critiques of EP take many forms. Indeed, there now seems to be a small publishing industry dedicated to the polarities of claim and counter-claim. Few would argue against the notion that looking at evolution is essen-tial for understanding current behaviour. The disputes mainly concern a particular interpretation of EP. This is sometimes termed the ‘Santa Barbara school’, named after the University of California location of its principal disciples (Tooby and Cosmides, 1990).

One point of criticism is that this school of evolu-tionary psychologists put their faith in what they term modules, special-purpose processors, each of which is dedicated to solving a particular problem. For example, the human brain would be described as being made up from such modules as a jealousy module, dedicated to detecting and acting upon threats as in sexual infidelity. Another such module is described as a cheating detec-tion module. EP suggests that our mind is equipped with dedicated processes that alert us when someone is trying to cheat us, as in an unfair exchange of goods. Modules are something like cognitive equivalents of reflexes – fast, automatic and dedicated, with each solving just a single problem.

Tooby and Cosmides use the analogy of a Swiss army knife, a tool equipped with a number of components such as a knife and a can-opener, each serving just one particular function. You would have some difficulty in trying to use the can-opener to pull a cork from a wine bottle.

Critics of EP argue along two lines. First, they deny that we are quite as modularized (‘compartmentalized’) as EP suggests. Second, they suggest that, although some modularization of the brain does occur, EP has misunderstood its determinants. EP is said to put too much weight upon genetic factors and insufficient upon development. In fact, we turn out as we do as a result of the subtle dance between genes and environment. As noted earlier, a skill at riding a bicycle does not arise from genes producing a particular ‘cycling module’ – as one critic memorably expressed it, there were surely rather few bicycles around in our early evolution for this skill to be genetically encoded as a module! In reality, it emerges as the result of a combination of genes encod-ing for a brain with a broad capacity for controlling balance and early learning of the particular motor skills involved in balancing a bicycle. The behaviour becomes automatic (‘modularized’) with practice.

EP and the critiques of it are a particularly good demonstration of the need to bring together different types of explanation. EP is based firmly in the tradition of functional and evolutionary explanation. However, its conclusions need to match an understanding of the possibilities arising from the brain and its development. Later chapters will explore the relevance of EP to such topics as emotion, feeding and sexual motivation. We now turn to a case study that will serve to bring together the different types of explanation.

Reference:
Toates, Frederick. 2011. Biological Psychology 3rd edition. England: Pearson Education.