An interesting study in Nature Neuroscience (December 1, 2006). It seems that male and female fruit flies have different styles of aggressive behavior. Males slug it out. Females push and shove. Why am I not surprised? It sounds so -- so playground.
Now Barry Dickson and his colleagues at the Research Institute of Molecular Pathology in Vienna have identified a gene called fruitless that determines the difference. Further, they engineered male flies with a female variant of the gene, and female flies with a male variant. Sure enough, the modified males shove, and the modified females box.
Ah, now if only we could do some similar genetic jiggering in humans, replacing the fist-and-gun gene in males with a female open-palm shove variant. Much less lethal.
We have lots yet to figure out about the biological and cultural components of violent behavior, but it seems pretty clear there's an innate difference by sex. Some years ago, Russell Fernald, a neurobiologist at Stanford University, studied African cichlid fish in Lake Tanganyika. He found that bullying, violent males developed bigger brain cells in the hypothalamus, which in turn caused the fish to develop large testes and bright body colors. Wimpish, nonviolent male fish had smaller brain cells, shrunken testes, and drab sand-colored scales. You can guess which male fish get the cichlid chicks.
Here's a thought: Perhaps women could help the world evolve to a more peaceful place by consistently expressing a sexual preference for wimpish, nonviolent guys like me.