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Major transitions in evolution


Molecular clocks
John Maynard Smith Scientist
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If the neutral theory is true, then molecular clocks are fine. If the molecular... there's a lot of controversy about whether they are true, and I mean, by and large, my feeling about clocks is that the neutral theory is near enough true to make the clocks fairly reliable. But there has been a big problem with bacteria. To discover whether the clock in bacteria goes at the same rate as a clock in mammals, let's say, because we don't have any fossil bacteria. But the problem has ultimately been solved by a group of people, the only one I actually know is Nancy Moran, who was a student in Ann Arbor when I was there, who have got the clock calibrated by realising that aphids - greenfly and things like that - have endosymbiotic bacteria, and you can show... and they're transmitted in the egg by the aphid, so that the mother gives it to her daughters. And it turns out that the phylogenetic tree of the aphids and of the bacteria are identical. And since you can date the branching of the aphids, by amber and things of that kind, you know the branching of the bacteria, and you can ask how fast is the clock going. And it really is going surprisingly similarly to that in the aphid, I mean, it really is a very striking observation, to me a bit unexpected, for various reasons. But it really does look as if the bacterial clock is not greatly different in rate to the... the clock for the rest of the world.

[Q] Shouldn't you be able to use the molecular clock to test the idea that there was a Cambrian explosion, by looking at say, I don't know, annelid and mollusc DNA and seeing whether you really can trace them back to the Cambrian and whether they would trace back to some time in the pre-Cambrian?

I think the clock obeys Maynard Smith's rule about numbers in biology, which is that they're always right to a factor of two. And when I say I believe the molecular clock, I do believe it to a factor of two, I do not believe it to a factor of 10%. And to get Cambrian versus pre-Cambrian, which is, after all, 600 million years ago, I think the error is too big to enable you to do that. It is clear, from the molecular clock, that... that the radiation of the main groups was reasonably rapid, but it could have been a 100 million years. I mean, it could have been slow by genetic standards but fast by paleontological ones.

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: Ann Arbor, Nancy Moran

Duration: 2 minutes, 38 seconds

Date story recorded: April 1997

Date story went live: 24 January 2008