SCIENCE / Sexual Milestones

1884 August Weismann points out that sex is not essential for reproduction.

1930-32 R A Fisher and H J Muller independently explain sex as a mechanism for spreading genetic innovations.

1964 'Muller's Ratchet' theory devised to explain why genetic defects accumulate unless countered by sex. This revises an old idea that sex has a rejuvenating effect on the species.

1966 In a book called Adaptation and Natural Selection, Professor George Williams attacks the idea that sex could be good for the species but bad for the individual.

1978 John Maynard Smith publishes The Evolution of Sex, a book that expresses the increasing bafflement of biologists.

1980 William Hamilton and others independently argue that sex is a mechanism for perpetually changing genetic defences against parasites: the Red Queen theory.

1990-93 Experiments by Curtis Lively and simulations by Hamilton and others provide more backing for Red Queen theory.