The Mating Mind by Geoffrey Miller, Heinemann/Doubleday,
拢20/$27.50, ISBN 0434007412
ABOVE my desk is a postcard from a friend showing two caddis larvae in cases
they themselves constructed from fragments of real gold, tiny pearls and
precious stones. This bio-jewellery is easy enough to create. You simply extract
a caddis larva from its usual gritty home, provide it with some expensive
building materials, and sit back and wait. The caddis larva鈥檚 home, or case, is
a classic example of what Richard Dawkins calls an 鈥渆xtended phenotype鈥濃�攁
product of an individual鈥檚 genes that exists outside its body.
In The Mating Mind, Geoffrey Miller suggests that most of the
products of human culture鈥攊ncluding the cave paintings in Font-de-Gaume,
Rachmaninov鈥檚 third piano concerto and the ceiling of the Sistine
Chapel鈥攁re extended phenotypes. In contrast to the caddis fly鈥檚 protective
case, which has clear survival value and which evolved through natural
selection, Miller鈥檚 view is that human artistic achievements have evolved
through sexual selection.
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In Miller鈥檚 world, David Beckham鈥檚 ability to kick a ball into a net and
Picasso鈥檚 artistic output evolved because they increase male reproductive
success. There is a precedent. The males of 18 species of bowerbirds build
elaborate twig huts or 鈥渁venues鈥� which they decorate with scarce and beautiful
objects, including mollusc shells and fruit. The males with the most impressive
bowers attract and copulate with the most females. It is a sexually selected
extended phenotype.
Despite centuries of speculation, there has until now never been a satisfying
or convincing answer to the question 鈥渨hat is art for?鈥� Neither has there been,
despite more than a century of speculation, an answer to why the human brain is
capable of such sophisticated performances. It is hard to see what relevance the
intellectual ability to design a computer or sculpt a David could have
had in pre-literate society.
Here Miller develops and elaborates the idea, first alluded to by Herbert
Spencer in the late 19th century, that like the tail of the male argus pheasant
a large part of the human mind is the product of sexual selection rather than
natural selection. The logic is as follows: while natural selection produces
traits that aid the individual鈥檚 survival in some way, sexually selected traits
do exactly the opposite. The argus pheasant鈥檚 feathery appendage is an
encumbrance, a hindrance and a handicap. But because it renders its owner more
attractive to females than less elaborately ornamented males, it pays for itself
through increased reproductive success.
In natural selection, the environment does the selecting. With sexual
selection it is members of one鈥檚 own species that act as the selective agents.
As Miller says, with sexual selection 鈥済enes act as both fashion models and
fashion critics鈥�, creating feedback loops that can result in extraordinary and
rapid evolution.
Miller鈥檚 account of current sexual selection theory is one of the best I have
read. He also makes the important point that most people鈥檚 view of evolution is
simultaneously shaped and constrained by Spencer鈥檚 quip 鈥渟urvival of the
fittest鈥�. By concentrating on 鈥渟urvival鈥�, the focus is turned towards natural
selection. This, he says, has given us a distorted view of evolution, and we
have missed out on the tremendous explanatory power of sexual selection.
This may account for the neglect of Charles Darwin鈥檚 brilliant idea to
explain the often dramatic differences between males and females. He described
two processes: competition between males (for females) and female choice (of
males). Horns, teeth, spurs, spikes and claws make males more effective fighters
and evolved through male-male competition. But useless features such as silky
plumes, warty wattles, fancy songs and bowers evolved through female
choice鈥攂ecause females found them attractive. Miller鈥檚 main message is
that our relatively huge, energy-guzzling but staggeringly capable brains
evolved as a result of female choice.
The immediate implication of this is that females preferred, and probably
still prefer, to mate with males with better brains. This suggests that, just as
with pheasant tails, male brains should have evolved to be bigger than those of
females. Miller tells us that the average human male brain weighs 1440 grams and
the female brain 1250 grams. After taking the differences in body size into
account, this reduces to males having 100 grams more grey matter than
females.
There is precious little evidence that this 8 per cent difference translates
into higher IQ among men than women, although there are some small differences
in cognitive ability between the sexes. On the other hand, there are dramatic
sex differences in the tendency to signal creative ability鈥攖o make a
display of it, you might say. For almost every activity you can think
of鈥攂ullfighting, breeding racing pigeons or writing books鈥攎ales do
it more, and more competitively, than females.
They also do it most between the ages of 20 and 30 years, a time of life when
sexual competition and courtship activities are at their peak. All this suggests
that sexual selection has favoured males that excelled in these
activities鈥攖hough Miller does point out that we must be careful in drawing
such a conclusion. Differences between the sexes鈥� creative abilities are rapidly
eroding as opportunities for women in Western societies increase. In other
words, the relationship between gender and creativity is confounded by the
cultural repression of women, and we should be aware that sex differences in
showing off these skills may be more apparent than real.
If males really are better show-offs, then there is a rather simple
explanation for the smallness of the difference in brain size between the
sexes鈥攃ompared with the differences in other primates鈥攁nd one which
is consistent with the fact that humans have relatively large brains. A large
brain may be necessary for males to be able to perform intellectual pirouettes,
but females may require an equally large brain to be able to make sure they are
doing them properly and to be certain they can distinguish genuine from faked
ability. If, on the other hand, males and females do not differ in their basic
tendency to advertise their abilities, then similar-sized brains in the two
sexes can be explained by mutual mate choice.
Although this is a work of advocacy, Miller is, compared with most
evolutionary psychologists, remarkably honest about the limitations of his
ideas. He admits that what he has presented is no more than a
theory鈥攁lbeit a powerful one. But as with much evolutionary psychology,
the question I ask myself is how does one actually test these ideas? Without a
concerted effort to do this, evolutionary psychology will remain in the realms
of armchair entertainment rather than real science.