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Are mammals stuck with sex?


Viviparity may be a big evolutionary mistake!
John Maynard Smith Scientist
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[Q] You were pointing out the sporadic distribution of asexual reproduction in the taxonomic tree, and you said, 'Wouldn't it be nice if we could find something else that had the same kind of sporadic distribution,' but you never actually said whether you'd found any such examples.

Well, I've not done the serious statistics. I mean, nowadays, you know one has to do proper statistics before you would justify a statement of that kind. But I have a candidate which I would like somebody to do the statistics on, and it's rather an unexpected one. It's the habit of producing your young alive, viviparity. Now, you think, come on, that can't be right, all mammals are viviparous, you know, one big taxonomic group. I think the fact that mammals are all viviparous is a little like the Bdelloid rotifers all being parthenogens. It's... it's a curious quirk. By and large, viviparity crops up, particularly in the vertebrates, in a very irregular way.

[Q] It's very sporadic in teleost fish.

That's right. I would like to see somebody do a serious statistical survey of the distribution of viviparity in the vertebrates. And I think they might find that mammals are really weird, in being... clearly mammals, it's an invention that's succeeded.

[Q] It's just one datum.

It's one datum in the statistics. I think someone, you know, your colleague, Paul Harvey, or one of his students, should have a serious go at it. Maybe there are others, I've not got a good example.

[Q] But in order for the analogy with asexuality to be correct, it would have to be the case that... I mean you would have to be predicting that viviparity, when it arises, quickly drives the species extinct, wouldn't you?

That's right, yes.

[Q] Is that what you want to say?

If that's what the data says, that's what I want to say, yes, I think it's a terrible mistake. 

[Q] There are other things, like halpo-diploidy, which have the opposite kind of distribution, which are not sporadic, which really do characterise major taxa.

Yes, again, when I originally put forward the argument that the taxonomic distribution of parthenogenesis was... was patchy, I did use the haplo-diploids as a counter example to show that other breeding systems could, if they arose, spread to whole groups, and it... you didn't very often get this occasional example. But I'm afraid I didn't do the statistics properly, I mean, somebody should. In those days, you see, you could make these kind of statements without doing the statistics. Nowadays, the whole thing has... the rules of the game have changed and you have to do it properly, I'm afraid.

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: Paul Harvey

Duration: 2 minutes, 50 seconds

Date story recorded: April 1997

Date story went live: 24 January 2008