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Explaining the maintenance of sex


Which is better: parthenogenisis or sexual reproduction?
John Maynard Smith Scientist
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Such a gene would be passed on to all the offspring instead of to only half the offspring, as happens in ordinary sexual reproduction, therefore such a gene would double in frequency in every generation, and really, in an extremely short space of time, the whole species will be taken over by ameiotic parthenogenesis. Now, this isn't an imaginary scenario, I mean, there are organisms out there that do exactly that, including quite complex organisms. The ones closest to ourselves are lizards. Some lizards are... the whole species consists of a set of genetically identical females, all producing offspring genetically to themselves, no males. And you get these both in Europe and in America. So it's perfectly possible, the problem is, why doesn't it happen? It mean, it's really quite a severe problem that, in the short run, parthenogenesis has this very strong, twofold advantage, and yet the great majority of organisms still do it sexually rather than parthenogenetically. So I think it clearly did present a problem.

[Q] That, of course, presupposes that the parthenogenetic female is capable, economically, of having the same number of offspring as a sexual female would. If the sexual female got a lot of help from her mate and had twice as many offspring, the problem wouldn't arise, would it?

No, that's absolutely right, and that's why I wanted to talk about codfish and not humans, because humans, at least there's the idea that males help to look after their children, I'm not sure that it's really true. But in any species in which the male really contributes as much as the female to feeding and raising the young, then the argument wouldn't apply. It also, it's quite important that it did not apply to the time of the origin of sex, because the first organisms reproducing by producing gametes which then fuse, were what we call isogamous, i.e. equal gametes, there was no differentiation between eggs and sperm, it was just a fusion of two equal sized cells. And if you sit down with a pencil and paper and think about that, there isn't, any longer, a twofold advantage of abandoning sex. So it's really a problem that in the form I presented it, of the maintenance of sexual reproduction, rather than its origin, and it's a problem which applies only to organisms, as you say, in which males don't contribute very much.

The late British biologist John Maynard Smith (1920-2004) is famous for applying game theory to the study of natural selection. At Eton College, inspired by the work of old Etonian JBS Haldane, Maynard Smith developed an interest in Darwinian evolutionary theory and mathematics. Then he entered University College London (UCL) to study fruit fly genetics under Haldane. In 1973 Maynard Smith formalised a central concept in game theory called the evolutionarily stable strategy (ESS). His ideas, presented in books such as 'Evolution and the Theory of Games', were enormously influential and led to a more rigorous scientific analysis and understanding of interactions between living things.

Listeners: Richard Dawkins

Richard Dawkins was educated at Oxford University and has taught zoology at the universities of California and Oxford. He is a fellow of New College, Oxford and the Charles Simonyi Professor of the Public Understanding of Science at Oxford University. Dawkins is one of the leading thinkers in modern evolutionary biology. He is also one of the best read and most popular writers on the subject: his books about evolution and science include "The Selfish Gene", "The Extended Phenotype", "The Blind Watchmaker", "River Out of Eden", "Climbing Mount Improbable", and most recently, "Unweaving the Rainbow".

Tags: ameiotic parthenogenesis, lizards, cod, mating, sex

Duration: 2 minutes, 26 seconds

Date story recorded: April 1997

Date story went live: 24 January 2008