In psychology last year I learned of an experiment testing this. Dogs were placed in one part of a two-chambered cage with a gate blocking them from moving from chamber to chamber. A tone was sounded and an painful electric shock went through the floor of the cage a few seconds later. Without a way to escape, the dogs soon succumbed to the classic signs of stress - urination, defecation, whimpering and huddling down on the floor without moving - whenever the tone rang.

A control group of dogs was then placed into identical cages and the barrier between the chambers were removed. The shocks started up again and the control dogs soon figured out that they could stay in the other chamber and be safe from shocks. The other group of dogs just stayed hunkered on the floor, unable to escape due to learned helplessness. I've seen it in humans and it's hard to live with and hard to break. Another reason why child abusers should be exterminated.