I always wonder that too. Then I think reality is just too messy for the nice dualistic explanation. My current hypothesis is this. At one point in time, prior

I always wonder that too. Then I think reality is just too messy for the nice dualistic explanation. My current hypothesis is this. At one point in time, prior to the accepted exit date for the "Out of Africa" hypothesis, various populations of intermittently isolated but still interbreeding groups of descendants of Erectus existed. Their maximal range stretched from the Cape in Africa in the South to Europe and Asia in the North. At some point, one of these groups got stuck in an isolated environment with a small population. Our genetics show that all modern humans are descended from a breeding population of a few thousand individuals. While in the midst of this "Great Pinch," this population evolved a "killer app," most likely making extreme use of our strong but tactile hands coupled to our (comparatively) massive glucose-gobbling brains. Through chance event they then reintegrated with the breeding populations similar enough to them to produce fertile offspring. But those with more sapiens like genes received such a genetic advantage, that they were able to spread those genes far and wide, until all the human-like species were destroyed or submerged in H. Sapiens. What was that killer app? I don't know. But some fundamental sea shift occurred when our population dwindling so low: perhaps true language, or maybe larger group size through religion. But its defining feature seemed to be that it enabled mass organization on a large scale, larger than was possible in simple hunter-gatherer bands. The basic "tribal culture" of humanity, in which we can extend our imagined community of kin beyond the next mountain range, is the manifestation of that change. Even the most untouched hunter-gatherer bands we encounter have some sort of allegiance to a larger group, which was often termed "tribe." Imagine hunter-gatherer warfare vs. tribal warfare. Your total numbers constrained by Dunbar's number while your enemy can call consistently call upon thousands of loosely allied bands to come to his aid. It reconciles both "Out of Africa" with the increasingly bizarre findings that of human-like artifacts predate the theory's predicted exit time. It's too bad, I would have rather liked to talk to a Denisovan or Neanderthal. At this time, I'd like to note that I wish I was an evolutionary biologist, or that one would be kind enough correct me :)