The Queen - Matt Ridley

In all three fields the breakthrough was to abandon notions of stability: Lotka and Volterra were interested in knowing whether parasites could stably control populations of hosts; Haldane was interested in what kept polymorphisms stable for so long. Hamilton was different. "Where others seem to want stability I always hope to find, for the benefit of my idea of sex, as much change and motion . . . as I can get.""

The main weakness of the theory remains the fact that it requires some kind of cycles of susceptibility and resistance; the advantage should always be swinging back and forth like a pendu-lum, though not necessarily with such regularity: 66 There are some examples of regular cycles in nature: Lemmings and other rodents often grow abundant every three years and rare in between: Grouse on Scottish moors go through regular cycles of abundance and scarcity, with about four years between peaks, and this is caused by a parasitic worm: But chaotic surges, such as locust plagues, or much more steady growth or decline, such as in human beings, are more normal: It remains possible that versions of the genes for resistance to disease do indeed show cycles of abundance and scarcity: But nobody has looked. b7

THE POWER OF PARASITES

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THE RIDDLE OF THE ROTIFER

Having explained why sex exists, I must now return to the case of the bdelloid rotifers, the tiny freshwater creatures that never have sex at all—a fact that John Maynard Smith called a "scandal. " For the Red Queen theory to be right, the bdelloids must in some manner be immune from disease; they must have an alternative antiparasite mechanism to sex: That way they could:be exceptions that prove the rule rather than embarrass it:

As it happens, the rotifer scandal may be on the verge of a solution. But in the best traditions of the science of sex, it could still go either way. Two new theories to explain the sexlessness of bdelloid rotifers point to two different explanations.

The first is Matthew Meselson 's: He thinks that genetic insertions—jumping genes that insert copies of themselves into parts of the genome where they do not belong—are for some reason not a problem for rotifers. They do not need sex to purge them from their genes. It 's a Kondrashov-like explanation, though with a touch of Hamilton: (Meselson calls insertions a form of venereal genetic infection:) 68 The second is a more conventional Hamilton-ian idea: Richard Ladle of Oxford University noticed that there are groups of animals capable of drying out altogether without dying—losing about 90 percent of their water content. This requires remarkable biochemical skill. And none of them have sex.

They are tardigrades, nematodes, and bdelloid rotifers: Some rotifers, remember, dry themselves out into little "tuns " and blow around the world in dust: This is something ,sexual monogonont rotifers cannot do (although their eggs can). Ladle thinks that drying yourself out may be an effective antiparasite strategy, a way of purging the parasites from your body. He cannot yet explain exactly why the parasites mind being dried out more than their hosts do; viruses are little more than molecular particles, in any case, and so could surely survive a good drying. But he seems to be on to something. Those nematode or tardigrade species that do not dry out are sexual. Those that can dry out are all female:'

The Red Queen has by no means conquered all her rivals: Pockets of resistance remain. Genetic repair diehards hold out in

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The Red Queen

places like Arizona, Wisconsin, and Texas. Kondrashov 's banner still attracts fresh followers. A few lonely tangled bankers snipe from their laboratories. John Maynard Smith pointedly calls himself a pluralist still. Graham Bell says he has abandoned the "mono-lithic confidence " (in the tangled bank) that infused his book The

Masterpieceof Nature, but has not become an undoubting Red Queen-er. George Williams still hankers after his notion that sex is a historical accident that we are stuck with. Joe Felsenstein maintains that the whole argument was misconceived, like a discussion of why goldfish do not add to the weight of the water when added to a bowl. Austin Burt takes the surprising view that the Red Queen and the Kondrashov mutation theory are merely detailed vindications of Weismann's original.idea that sex supports the variation needed to speed up evolution—that we have come full circle. Even Bill Hamilton concedes that the pure Red Queen probably needs some variation in space as well as time to make her work. Hamilton and Kondrashov met for the first time in Ohio in July 1992 and agreed convivially to differ until more evidence was in. But scientists always say that: Advocates never concede defeat. I believe that a century hence biologists will look back and 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:

Chapter 4

GENETIC MUTINY AND

GENDER

The turtle lives

'twixt plated decks

Which practically conceal its sex:

I think it clever of theturtle

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" ' 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.