What turns an ordinary person into a killer? The idea that a civilised human being might be capable of barbaric acts is so alien that we often blame our animal instincts – the older, “primitive” areas of the brain taking over and subverting their more rational counterparts. But fresh thinking turns this long-standing explanation on its head. It suggests that people perform brutal acts because the “higher”, more evolved, brain overreaches. The set of brain changes involved has been dubbed Syndrome E – with E standing for evil.