The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [19]
John Maynard Smith, an engineer turned geneticist at the University of Sussex in England with a penetrating and somewhat playful mind that had been trained by the great neo-Darwinist, J. B. S. Haldane, answered Ghiselin’s question without solving his dilemma. He said that a sexual gene could spread only if it doubled the number of offspring an individual could have, which seemed absurd. Suppose, he said, turning Ghiselin’s thought around, that in a sexual species, one day a creature decides to forgo sex, and put all of its genes into its own offspring, taking none from its mate. It would then have passed twice as many genes on to the next generation as its rivals had. Surely it would be at a huge advantage. It would contribute twice as much to the next generation and would soon be left in sole possession of the genetic patrimony of the species.19
Imagine a stone-age cave, inhabited by two men and two women, one of them a virgin. One day the virgin gives birth ‘asexually’ to a baby girl that is essentially her identical twin (she becomes, in the jargon, a parthenogen). It could happen in several ways, for example by a process called automixis, in which an egg is, roughly speaking, fertilized by another egg. The cave woman has another daughter two years later by the same means. Her sister, meanwhile, has had a son and a daughter by the normal method. There are now eight people in the cave. Next, the three young girls each have two children and the first generation dies off. Now there are ten people in the cave, but five of them are parthenogens. In two generations, the gene for parthenogenesis has spread from one-quarter to one-half of the population. It will not be long before men are extinct.
This is what Williams called the cost of meiosis and Maynard Smith called the cost of males. For what dooms the sexual cave people is simply that half of them are men and men do not produce babies. It is true that men do occasionally help in child rearing, killing woolly rhinos for dinner or whatever, but even that does not really explain why men are necessary. For suppose that the asexual women at first gave birth only when they had intercourse. Again there are precedents. There are grasses that only set seed when fertilized by pollen from a related species, but the seed inherits no genes from the pollen. It is called pseudogamy.20 In this case, the men in the cave would have no idea that they were being genetically excluded and would treat the asexual babies as their own, serving up woolly rhino meat just as they would to their own children.
This thought-experiment illustrates the numerically huge advantage a gene has that makes its owner asexual. Logic such as this set Maynard Smith, Ghiselin and Williams to wondering what compensating advantage of sex there must be, given that every mammal and bird, most invertebrate animals, most plants and fungi, and many protozoa are sexual.
For those who think that to talk about the ‘cost of sex’ is merely to illustrate how absurdly pecuniary we have become, and who reject the whole logic of this argument as specious, I offer the following challenge: explain hummingbirds. Not how they work, but why they exist at all. If sex had no cost, hummingbirds would not exist. Hummingbirds eat nectar, which is produced by flowers to lure pollinating insects and birds. Nectar is a pure gift by the plant of its hard-won sugar