This theory has not been proven as fact at all. It is and will remain a theory! As noted in the chapter on Human Evolution, the THEORY of Human Evolution
This is used as an excuse for intolerable animal like behaviors that people succumb to.. they now blame their inherent traits and characteristics. This again is not proven as fact though it is taught in schools —where they teach evolution. There are ways to disprove the theory.
Reference:
The Living Environment; Biology by Rick Hallman, AMSCO Publication