Feminists

Recent research on psychopathy suggests that it's promoted by a defect on the X-chromosome. X-linked genetic problems are more likely to show up in males, since most females have another perfectly good X to cancel out the bad one.

Biology is rarely destiny, though, except in cases of such overwhelming genetic defects that a normal life is near impossible. Most men who have the gene will never become serial killers - the scientist who did the study is one such. It takes the combination of a bad gene and a violent upbringing to bring it out. Also, some women can be so damaged by trauma that they become killers: Aileen Wuornos comes most readily to mind.

I'm a TED addict, and I found this talk fascinating:

http://www.ted.com/talks/jim_fallon_exploring_the_mind_of_a_killer.html