Though we most often tend to identify the crime of rape as one that is primarily an assault on women by men, as you have identified, women are quite capable of the atrocity as well. Same sex assaults or male-male and female-female prison rape are quite common and may be the least reported form of rape, according to some studies. While I tend to agree that rape is less often a crime of sexual passion than one related to power and dominance, there are a number of contributing factors under study. I wonder how much the changing role of women in society is contributing to a sense of insecurity in some individuals, which may be translating into sexual aggression? That comment from a North American perspective, as in other parts of the world rape may have completely different motivation and bias.