In species where the only thing that a male contributes to his offspring is his sperm, he is usually, as theory predicts, more or less indiscriminate in his courting.

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As a result, dead males may act as plugs to prevent other males from copulating, ensuring that the suicidal male, not a rival, fathers the offspring.

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These eggs were then transplanted into a female mouse and healthy offspring were born who grew into fertile male and female adult mice.

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Another possibility, said Dr Crisanti, would be a modification in male mosquitoes which led to the death of any female offspring.

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By combining her genes with a male's, a female halves her genetic contribution to her offspring, and subsequent generations see it halved again and again.

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Greater promiscuity in females does, indeed, lead to bigger testes, presumably because a male needs to make more sperm to have a fighting chance of fathering offspring, if those sperm are competing with sperm from a lot of other males.

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Such food, whether it be a neatly wrapped fly, or the body of the dead male, provides nutrients for the female, allowing her to produce bigger or more numerous offspring, to the ultimate benefit of the father's genes.

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Second, as far as it is possible to tell, male frogs contribute nothing to the welfare of females, nor do they contribute anything to their offspring except their genes.

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Indeed, Wolbachia's genes are so manipulative that they can convert male insects to females, kill males, induce virgin birth in females and even cause the offspring of males to die unless they carry the very same strain of Wolbachia as the father.

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