In the social sciences, atavism is a cultural tendencyfor example, people in the modern era reverting to the ways of thinking and acting of a former time.
Hints of long-extinct creatures, echoes of evolution past, occasionally emerge in real life -- they're called atavisms, rare cases of individuals born with characteristic features of their evolutionary antecedents.
Both the brains and skulls of criminals demonstrated evidence of atavism; in other words, criminals were evolutionary throwbacks, no less, and their skulls and faces bore the signs of degeneration.
