But it's also a scene played out in the sex life of the Tanzanian cockroach Nauphoeta cinerea . Female cockroaches prefer males at the bottom of the social pecking order, and dominant males try and stop them from having their way. But when females do get the low-ranking man of their dreams, they produce fewer sons, apparently in an effort to avoid passing on his wimpishness. This seems to be the price that females are willing to pay to avoid the injuries that can result from encounters with stronger, aggressive males, Allen Moore, of the University of Manchester, UK, and colleagues now suggest 1 .
Male cockroaches let each other know how tough they are by producing a pheromone.
How females control the sex of their offspring is unclear, but by having fewer sons they may reduce the competition between males in the next generation, giving their sons a better chance of winning a mate. But Forsgren is puzzled as to why a female's choice should result in her having fewer male offspring. But there are about a dozen species, from moths to birds to salamanders, where this has been shown not to be the case. Male and female animals often have very different ideas about whether mating would be a good thing or not. This leads to an arms race, with the sexes evolving ways to manipulate each other, and to dodge manipulation.