Cain was a leftist; Abel was a conservative
This refers to studies that show leftists tend to prioritize things like rocks and trees and the abstract idea of people rather than actual people and in particular people with whom they're close.
Conservatives are the opposite. The problem of course is that the left's (Cain's) priorities dampened empathy for those close, allowing them to be ruthless and often win in the short run. Conservatives' (Abel') natural brotherly empathy made him vulnerable and easily preyed upon. Hence Cain was able to kill Abel. And it's repeated throughout history.
