"The term atavism is sometimes also applied in the discussion of culture.  Some social scientists[who?] describe the return of older, "more primitive" tendencies (e.g. warlike attitudes, "clan identity", anything suggesting the social and political atmosphere of thousands of years ago) as "atavistic". "Resurgent atavism" is a common name for the belief that people in the modern era are beginning to revert to ways of thinking and acting that are throwbacks to a former time. This is especially used by sociologists in reference to violence."

Irrational hate crimes have led to massacres and destruction so why do people still do it?  Why are rational Americans acting just like the detested "irrational"  jihadists?