It's always been vaguely worrying that mice and men (sorry, don't mean to be sexist, just couldn't resist the alliteration and, of course, the Burns' reference) are so similar that their reactions in lab experiments are (rightly) considered indicative of human responses. Here's an interesting example -- 3 years ago, researchers quite accidentally deleted from a strain of lab mice a gene that's important for brain development. In so doing, they turned the mice into rabidly aggressive little monsters (in the behavioral sense! I don't mean to imply they were deformed in any way). Understandably intrigued by this, the researchers decided to give the next generation the human version of the gene they were missing, and voila, the nasty turned nice!

Does this mean we can breed aggression out of the human race? (Should we if we could?)