As follows: The distribution of already existing traits, changes pretty fast (20-50 generations is fairly much) when the environment and evolutionary pressure c

As follows: The distribution of already existing traits, changes pretty fast (20-50 generations is fairly much) when the environment and evolutionary pressure changes. And, large parts of the planet, haven't been invaded and the men killed, women raped, the last hundreds of years, in some places not even the last thousand years. Then, violent traits (reproducing by killing all men in the tribe nearby, raping the women) start fading away. (Not noticeable in a single lifetime though)