The article stated that the tame fox specimen exhibited facial features that were slightly different from those of wild foxes, and that the tamer they were, the greater the differences were. Their jaws had become thinner, their chins less pronouned, and their eyes larger. The article noted that it was possible that these facial features were correlated with hormonal levels that made the foxes less aggressive and more tame, and that the same could be true in human beings.
Since human beings considers these facial features "attractive" in other human beings, it was possible to conclude that we're hardwired to be physically attracted to people whose facial features indicate a lower propensity to anger and aggression.
I've looked for the article on google but I can't find it unfortunately.