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existence. Let them consider the fungus. For many fungi are sexual, but they do not have males. They have tens of thousands of different sexes, all physically identical, all capable of mating on equal terms, but all incapable of mating with themselves.71 Even among animals, there are many, like the earthworm, that are hermaphrodites. To be sexual does not necessarily imply the need for sexes, let alone for just two sexes, let alone for two sexes as different as men and women. Indeed, at first sight, the most foolish system of all is two sexes, because it means that fully fifty per cent of the people you meet are incompatible as breeding partners. If we were hermaphrodites, everybody would be a potential partner. If we had ten thousand sexes, like the average toadstool, ninety-nine per cent of those you met would be potential partners. If we had three sexes, two-thirds would be available. It turns out that the Red Queen’s solution to the problem of why people are sexual is only the beginning of a long story.

CHAPTER FOUR

Genetic Mutiny and Gender

The turtle lives ’twixt plated decks

Which practically conceal its sex.

I think it clever of the turtle

In such a fix to be so fertile.

Ogden Nash

In the Middle Ages, the archetypal British village owned one common field for grazing cattle. Every villager shared the common and was allowed to graze as many cattle on it as he wanted. The result was that the common was often overgrazed until it could support only a few cattle. Had each villager been encouraged to exercise a little restraint, the common could have supported far more cattle than it did.

This ‘tragedy of the commons’1 has been repeated again and again throughout the history of human affairs. Every sea fishery that has ever been exploited is soon overfished and the fishermen are driven into penury. Whales, forests and aquifers have been treated in the same way. The tragedy of the commons is, for economists, a matter of ownership. The lack of a single ownership of the commons or the fishery means that everybody shares equally in the cost of overgrazing or overfishing. But the individual who grazes one too many cows, or the fisherman who catches one too many netfuls, still gets the whole of the reward of that cow or netful. So he reaps the benefits privately and shares the costs publicly. It is a one-way ticket to riches for the individual and a one-way ticket to poverty for the village. Individually rational behaviour leads to a collectively irrational outcome. The free-rider wins at the expense of the good citizen.

Exactly the same problem plagues the world of the genes. It is, oddly, the reason that boys are different from girls.

Why are People not Hermaphrodites?

None of the theories discussed so far explains why there are two separate genders.2 Why is everybody not a hermaphrodite, mixing its genes with those of others, but avoiding the cost of maleness by being a female, too? For that matter, why are there two genders at all, even in hermaphrodites? Why not just give each other parcels of genes, as equals? ‘Why sex?’ makes no sense without ‘why sexes?’ As it happens, there is an answer. This chapter is about perhaps the strangest of all the Red Queen theories, the one that goes under the unprepossessing name of ‘intragenomic conflict’. Translated, it is about harmony and selfishness, about conflicts of interest between genes inside bodies, about free-rider genes and outlaw genes. And it claims that many of the features of a sexual creature arose as reactions to this conflict, not to be of use to the individual. It ‘gives an unstable, interactive and historical character to the evolutionary process’.3

The 75,000 pairs of genes that make and run the average human body find themselves in much the same position as 75,000 human beings inhabiting a small town. Just as human society is an uneasy coexistence of free enterprise and social co-operation, so is the activity of genes within a body. Without co-operation, the town would not be a community. Everybody would lie and cheat