Changes to mouth and brain continued at a varying pace until modern humans evolved 100,000 to 200,000 years ago. But not until after agriculture began, a mere 8,000 to 10,000 years ago, did human societies begin to unveil their habits clearly. Evidence of real war comes soon after that unveiling. Both genders certainly contribute to these aggressive tendencies, but it is the male species that statistically are the main perpetrators. Altogether, American men are almost eight times as likely as women to commit violent crime.
More statistics follow.
In an effort to answer this question, 'Demonic Males' cites survey results of same-sex murders. And the thesis in the book is they probably would, but there are, of course, people willing to dispute that. That women would be just as bad as men. There's also the question as to whether there are genetic differences between men and women which would lead to different kinds of problem solving. You know, conflict will always occur, of course, in any kind of human situation, but if decisions were being made to serve women's interests rather than men's interests, then I think it's reasonable to argue that there would be a lower propensity for using violence than we see nowadays.