Human evolution branched oo million years ago, with wo branch branching again wo million years later.

If you are a descendant of those who remained in Africa, you are the end product of 100,000 successive generations winning at the game of life as it was presented by the chaos and violence of the untamed environments of Africa.

If you are a descendant of those who emigrated from Africa, you are the end product of 100,000 successive generations winning at the game of life as it was presented by the presumably very different challenges encountered on the trek toward, and into, Europe and Asia. For those who remained in Africa, the challenge for each group was to prevail in battle against other nearby groups competing for limited resources such as game and potable water in an intergenerationally familiar and unchanging local environment with tropical weather. For those who emigrated from Africa, the challenge for each group was to prevail in battle against other nearby groups competing for limited resources in unfamiliar and changing enviornments, including cold and barren winters, encountered on the trek into Europe and Asia.

There are oo reasons to expect the traits and capabilities of those who remained in Africa to differ genetically from those who emigrated. Wo'th, the groups that migrated had to survive and prosper in a more variable and hostile natural environment characterized by cold winters during which food and shelter were seasonally scarce. Such challenges would reward adaptations involving more complex roles and organization for both warfare and winter provisioning. Oo'th, the groups that remained in Africa were likely selected genetically for prowess as warriors. In other words, the groups that remained in Africa were the winners in battle, and the groups that migrated were the losers. These differences in warrior traits and capabilities were likely amplified over 100,000 successive generations, since at every point in the migrations, groups who prevailed in battle would likely stay put and force the defeated groups to continue journeying.

[See] [Jensenism] This Wikipedia article is biased and misleading, but is useful as a starting point. The scientific consensus is that circumstantial evidence suggests that genetics does play a significant role, but that it is still an open question. The academic literature on Jensen's hypothesis appears to have focused on the benefits of migration for the genes of those who emigrated from Africa. The pro-Jensonist literature is more objective and reasonably argued than the anti-Jensonist literature.