system
A chat on subreddit /r/NoStupidQuestions
human
Why? Most modern human behavior is nurture. Men's brains are not noticeably different from women's.

Nurture is literally the null hypothesis. Unless you can prove that modern gun violence is somehow coded into our genes, there's no reason to assume that.

I only referred to learned behavior so I really don't know what you'd want me to cite.
gpt
Differences in hormones could have an affect, think of roid rage.