This video, from neonas85, explains how selection for flight distance alone significantly changed the silver fox’s anatomy. Spots, curled tails, and floppy ears appeared simultaneously. Their hormonal levels were greatly changed, and the animals began to take on all sorts of novel shapes.

Domestic dogs, which have been domesticated for at least 10,000 years, have had a much longer time to develop these novel shapes.  One theory holds that the wolves that were less afraid of people were better able to scavenge off of us. Some wolves eventually adapted to living entirely off of human scraps and waste, and these wolves had much more reduced levels of fear. And as a consequence, their physical appearance changed in very much the same way as the silver foxes.

And that’s why dogs look and behave so differently from wolves.