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The idea of sexual selection


Courtship behaviour in Drosophila
John Maynard Smith Scientist
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I didn't mean to work on courtship behaviour and Drosophila, it was not planned in any way. What I was working on, which was really a project that I'd chosen myself, was the effects of inbreeding in general, but particularly, I mean,  using Drosophila as an experimental animal, and I was looking at the effects of inbreeding on fertility and rate of development and size and longevity and so on. And one of the things I discovered was that in an inbred line of Drosophila subobscura, this was, something like anything from 50 to 90% of the eggs failed to hatch. And I was puzzled by this. And one possible explanation was that they'd never actually been fertilised. And the first thing to do, the simple way, was just simply to make sure that the females had been mated, because obviously, if they hadn't been mated, the eggs wouldn't be fertilised. So, I can remember one morning setting up a large number of pairs, some of them an inbred male with an out-bred female, and some of them pairs of out-bred male and out-bred female, just to make sure the matings had taken place, so I was then going to collect eggs and count whether they hatched or not, and so on. And it was really quite astonishing that all the out-bred males mated with the female within five or ten minutes of putting them together, and almost none of the inbred males managed to mate with them. And I thought, well, there's something funny going on here, because it clearly wasn't the case that the inbred males were not trying, if one's allowed to use words like trying in animal behaviour. I mean, they were going through the whole courtship ritual, they were doing everything they ought to do, but the females were rejecting them. And so that led me to investigate courtship behaviour. But it wasn't, in other words, I wasn't led to this by the ethologists, I was led to it, as Helen would like me to be, I suppose, by the animals. The animals said, look, there's something funny going on here. And then I had a long, not debate, it was never printed, it was sort of long arguments in pubs and so on, really, particularly with Margaret Bastock, who was also working on courtship in Drosophila, and she was a student of Tinbergen's at the time.

[Q] And Mrs Manning.

Yes, she married Aubrey Manning, that's right. And I said, essentially, that the reason why the out-bred females are rejecting the inbred males is that when the out-bred female does her sideways dance, the inbred males can't keep up, and if they can't keep up, if they can't dance properly, the female rejects them. The out-bred males keep up fine and all's well. And the reason they don't keep up is that they can't, their eyesight's not good enough or their legs are not any good, or whatever, you know. And I could not persuade the young people in Oxford that this was the right interpretation. To me it was obvious, you know. But for them, at that time, if an animal didn't do something, it was because it wasn't motivated to do it. There was this notion of motivation. They had this internal sort of machinery, which was switched on by something called drive or motivation, and that what was wrong with my inbred males had to be they weren't motivated. And I said, 'Well, come on, now, they'll keep trying for an hour or so, and at the end of it, they'll get desperate and walk up behind the female and try jumping straight on. This doesn't look to me like a lack of motivation.' And I basically believe I was right. But it was quite interesting that, more generally, you see, the ethologists recognise what they called an instinct by the fact that it was a universal, all members of a species had to have it. And variation in behaviour had to be explained, therefore, by motivation... the differences. But they weren't really very interested in variation, they were interested in what was universal, whereas geneticists were interested in differences.

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: Drosophila subobscura, Drosophila, Oxford University, sexual selection, Margaret Bastock, Nikolaas Tinbergen, Aubrey Manning

Duration: 4 minutes, 6 seconds

Date story recorded: April 1997

Date story went live: 24 January 2008