Among humans the battle of the sexes seems to manifest itself in mostly unimportant ways--like spousal squabbles or celebrity sports challenges. But according to a report in the June 12 Proceedings of the National Academy of Sciences, gender conflict may actually play a significant role in nature: such clashes appear to spur the evolution of new species.

By studying related lineages of insects with different mating systems, researchers were able to assess how the systems affected the rate of speciation within each lineage. Previous studies had demonstrated the importance of mate selection in driving speciation, but the new research examined the reproductive conflicts that arise after mating has occurred. This postmating battle of the sexes, they say, arises from male competition to fertilize eggs. Complex interplay between male and female reproductive adaptations generates rapid coevolution of male and female reproductive physiology and morphology, eventually rendering populations from different regions unable to interbreed with one another--that is, they speciate. As predicted, those groups in which females typically mate with many males (a system known as polyandry) displayed much higher speciation rates--up to four times as high--than did groups in which females typically mate with a single male (monandry).