I grew up on a sheep farm. I disagree with this article. I found them to be almost pathologically fatalistic and idiotic. Perhaps there's something to be said about domestication having a negative cognitive effect, or inbreeding, or some other factor. But these animals were not intelligent.
Heck, I've done substitute teaching in a relatively affluent suburb of Austin, Texas and I find there are some really dim human creatures amongst us. Factors you noted all potentially relevant. It's frustrating to hear somebody say "Oh just reason with them!" when sometimes a certain contingent of 14 year olds are kind of lacking whip cracking in the bigger picture.
