Survival of the fittest

A poll of academics 20 years ago on the most influential thinker in the social and biological sciences would certainly have featured Marx and Freud near the top, along with Darwin. Today, however, Darwin bestrides both fields, while the Marxist sociologist is an extinct species and psychoanalysis is no more influential than any other Hampstead cult.

What's not fully appreciated, however, is just how many areas of research that don't have any obvious connection with evolution and the concept of the selfish gene are being transformed by a Darwinian approach.

Psychoanalysis itself, for instance, was subject to a devastating attack recently by Richard Webster in Why Freud Was Wrong. After providing chapter and verse for Freud's failure to cure any of his patients, Webster points out that the ancient Judaeo-Christian split between the spirit and the flesh is there at the heart of psychoanalysis - repackaged in the pseudo- scientific terms of the battle for mastery between the Ego and the Id.

What we need instead, Webster argues, is a model of human psychology that is based on Darwinian principles and rooted in the fact that our drives and responses have been shaped by evolution - that altruism, for instance, is no more a higher virtue than the sexual urge; both exist because they have survival value.

In fact, this is just one of the topics explored in The Moral Animal: the New Science of Evolutionary Psychology by Robert Wright (Little Brown) which looks at the way that male and female want different things out of relationships because evolution has shaped them in different directions.

Wright's idea, at its simplest, is that females need to be more choosy because not only do they invest more in their offspring - pregnancy, feeding - but they are unlikely to have more than about six. Males, on the other hand, can theoretically have an almost limitless number. As a result they have developed different mating strategies and look for different things - men being turned on by fertility, women by resources. It's an approach that has sparked a keen debate, not least because it suggests that male/female differences are not simply cultural.

But Darwinian insights apply not only at the level of men and women. Human Sperm Competition: Copulation, Masturbation and Infidelity, by Robin Baker and Mark Bellis (Chapman Hall), opens up a previously unexplored area of research in human sexuality.

In a long-running project at Manchester University, Baker has been looking, not at competition between males for mates, but at the competition between their sperm when inside a single female - something that happens in 4 to 10 per cent of conceptions. The result is something remarkable - a genuinely new book about sex.

Baker shows not only how men unconsciously customise their ejaculate to maximise their chance of having children, but also how women can use their orgasms to increase or decrease a partner's chance of being the one to impregnate her. In his scenario, sperm are not like marathon runners, all competing for the prize of fertilisation; they are more like members of an ant colony co-operating for a common good. Only a few are designed to fertilise; the rest are there to attack rival sperm.

Once a woman has become pregnant, the popular view holds that there is a lull in the relentless battle for supremacy that is a central element of the Darwinian model. Research by Dr David Haig of the Museum of Comparative Zoology at Harvard University, however, reveals a conflict of interests between the genes of the foetus and those of the mother. The mother's genes will be most successful if they ensure the survival of the foetus, but not at the expense of her ability to have other children.

However, each gestation is that foetus's only chance, so it wants all it can get. Haig shows how the battle is fought out with the weapons of glucose and insulin - the foetus pumping hormones into the mother's blood supply to increase the supply of glucose, and the mother producing more and more insulin to mop it up.

Immediately after birth, the Darwinian perspective changes things again. Instead of the mother simply creating a safe, cosy space to nurture the tiny creature, the implacable self-interest of the genes makes child-parent conflict inevitable.

A fascinating, if rather eccentric, account of the womb war and afterwards - eccentric because it is couched in terms of a synthesis between the Freudian and the Darwinian view - can be found in PsychoDarwinism by Christopher Badcock (Harper Collins).

Although sex and reproduction lie at the heart of the Darwinian view, ideas of selfish genes and cost/benefit ratios are just beginning to have an effect on fields as far apart as medicine and literature. Most of us are familiar with an evolutionary explanation for the rise of certain diseases, such as heart attacks, which seem to be linked to our affluent lifestyle; for several million years our hunter-gatherer ancestors got lots of exercise and ate small amounts of fat, so our bodies rebel when they are forced to endure a high-fat, low-exercise regime.

Recently, Rudolph Nesse and George Williams have widened this approach and applied it to medicine in general. In Evolution and Healing (Weidenfeld & Nicolson) they start from the basic evolutionary principle that the genes which code for our reactions to infection survive because they are useful - a fact that medicine currently ignores. For instance, the standard medical practice of bringing down a fever doesn't make sense from an evolutionary perspective. Fever is a strategy that many animals have developed to deal with infections because bacteria are highly sensitive to temperature: putting the temperature up a few degrees makes it much more difficult for them to reproduce. All sorts of treatments may soon change as a result of this approach.

If Joseph Carroll, Professor of English at the University of Missouri, is right, a big Darwinian-led upheaval is also in store for literature. In Literature and Evolutionary Theory (Missouri) he suggests that once you accept that our brains and bodies have been shaped by natural selection, you realise that our ability to tell stories is just as much affected by its survival value as is our ability to make tools.

Evolution focuses on behaviour that increases your chances of leaving a lot of offspring. The important factors include support for kin, men being worried that they are the father of a child, choosing the right mate, and incest avoidance. And these, he claims, are exactly the themes that arise endlessly in literaturen