The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [27]
But there is another odd thing about bdelloids besides their feats of endurance and fecundity. No male bdelloid rotifer has ever been seen. As far as biologists can tell, every single member of every one of all five hundred species of bdelloid in the world is a female. Sex is simply not in the bdelloid repertoire.
It is possible that bdelloid rotifers mix others’ genes with their own by eating their dead comrades and absorbing some of their genes, or something bizarre like that,1 but recent research by Matthew Meselson and David Welch suggests that they just never do have sex. They have found that the same gene in two different individuals can be up to thirty per cent different at points that do not affect its function – a level of difference that implies that bdelloids gave up sex between 40 million and 80 million years ago.2
There are many other species in the world that never have sex, from dandelions and lizards to bacteria and amoebae, but the bdelloids are the only example of a whole order of animal that entirely lacks the sexual habit. Perhaps as a result, the bdelloids all look rather alike, whereas their relatives, the monogonont rotifers, tend to be much more varied; they cover the whole range of shapes of punctuation marks. None the less, the bdelloids are a living rebuke to the conventional wisdom of biology textbooks – that without sex, evolution can barely happen and species cannot adapt to change. The existence of the bdelloid rotifers is, in the words of John Maynard Smith, ‘an evolutionary scandal’.3
The Art of Being Slightly Different
Unless a genetic mistake happens, a baby bdelloid rotifer is identical to its mother. A human baby is not identical to its mother. That is the first consequence of sex. Indeed, according to most ecologists, it is the purpose of sex.
In 1966, George Williams exposed the logical flaw at the heart of the textbook explanation of sex. He showed how it required animals to ignore short-term self-interest in order to further the survival and evolution of their species, a form of self-restraint that could only have evolved under very peculiar circumstances. He was very unsure what to put in its place. But he noticed that sex and dispersal often seem to be linked. Thus, grass grows asexual runners to propagate locally, but commits its sexually produced seeds to the wind to travel further. Sexual aphids grow wings; asexual ones do not. The suggestion that immediately follows is that if your young are going to have to travel abroad, then it is better that they vary, because abroad may not be like home.4
Elaborating that idea was the main activity of ecologists interested in sex throughout the 1970s. In 1971, in his first attack on the problem, John Maynard Smith suggested that sex was needed for those cases in which two different creatures migrate into a new habitat in which it helps to combine both their characters.5 Two years later Williams returned to the fray and suggested that if most of the young are going to die, as most who try their luck as travellers will, then it may be the very fittest ones that will survive. It therefore matters not one jot how many young of average quality a creature has. What counts is having a handful of young that are exceptional. If you want your son to become pope, the best way to achieve this is not to have lots of identical sons, but to have lots of different sons in the hope that one is good, clever and religious enough.6
The common analogy for what Williams was describing is a lottery. Breeding asexually is like having lots of lottery tickets all with the same number. To stand a chance of winning the lottery