That in the beginning the "domesticated" animals may have selected themselves by surviving because of human activity, like the wolves surviving on human waste/refuse, and humans didn't start from scratch when they began breeding animals.
That there may be some physical appearances that are linked to passivity, like white/spotted appearance and cowlick positioning.
That humans bred animals for traits they wanted is old news, but the two things above were new thoughts for me.
I'm beginning to think about it this way: it suggests that genetic engineering for this trait may have unintended consequences for some other trait. If personality traits have physical implications, then the converse is probably true as well.
It makes me think that the general idea of genetic engineering on humans is probably a very bad idea.