Sometimes it pays to be a wimpat least if you're a male cockroach. According to a study of the Tanzanian roach Nauphoeta cinerea published in the Proceedings of the Royal Society, females prefer low-ranking males to dominant ones any day. Trysts with weaklings, it seems, leave the females roaches in better shape than do encounters with more aggressive males. Yet when females do land a wimp (the high-ranking males do their best to thwart these couplings), they produce fewer sons. This, Allen Moore of the University of Manchester and his colleagues suggest, is the cost of the females' opting for safer sex.

Roaches aren't the only creatures in which females choose subordinate males. Previous studies have documented this preference in about a dozen species, including certain birds and salamanders. Exactly why the female roaches have fewer sons as a result of this choice, however, is a mystery. Paradoxically, producing fewer sons might actually maximize reproductive fitness: with fewer males in the next generation, the sons of these females with eyes for wimps might be more successful in themselves finding mates.