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.
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