declare that the Vicar of Bray fell down a tangled bank and was slain by the Red Queen. 7°
Sex is about disease. It is used to combat the threat from parasites. Organisms need sex to keep their genes one step ahead of their parasites. Men are not redundant after all; they are woman 's insurance policy against her children being wiped out by influenza and smallpox (if that is a consolation). Women add sperm to their eggs because if they did not, the resulting babies would be identically vulnerable to the first parasite that picked their genetic locks.
Yet before men begin to celebrate their new role, before the fireside drum-beating sessions incorporate songs about pathogens, let them tremble before a new threat to the purpose of their existence. Let them consider the fungus. 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!' Even among animals there are many, such as the earthworm, that are hermaphrodites. To THE POWER OF PARASITES
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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 50 percent 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, as does the average toadstool, 99 percent of those we meet 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:
GENETIC MUTINY AND
GENDER
—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' ' has been repeated again and again throughout the history of human affairs. Every sea fishery that has ever been exploited is soon overfished and its fishermen 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 behavior 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:' Why is every creature 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.''
The thirty thousand pairs of genes that make and run the average human body find themselves in much the same position as seventy-five thousand human beings inhabiting a small town.
Just as human society is an uneasy coexistence of free enterprise and social cooperation, so is the activity of genes within a body.
Without cooperation, the town would not be a community. Everybody would lie and cheat and steal his way to wealth at the expense of everybody else, and all social activities—commerce, government, education, sport—would grind to a mistrustful halt: Without cooperation between the genes, the body they inhabit could not be used to transmit those genes to future generations because it would never get built.
A generation ago, most biologists would have found that paragraph baffling: Genes are not conscious and do not choose to cooperate; they are inanimate molecules switched on and off by chemical messages: What causes them to work in the right order and create a human body is some mysterious biochemical program, not a democratic decision: But in the last few years the revolution begun by Williams, Hamilton, and others has caused more and GENETIC MUTINY AND GENDER
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more biologists to think of genes as analogous to active and cunning individuals. Not that genes are conscious or driven by future goals—no serious biologist believes that—but the extraordinary teleological fact is that evolution works by natural selection, and natural selection means the enhanced survival of genes that enhance their own survival: Therefore, a gene is by definition the descendant of a gene that was good at getting into future generations. A gene that does things that enhance its own survival may be said, teleologically, to be doing them
