Spread of Homo Sapiens

 ... relates to its generalist specialist status.  That is, the species Homo sapiens has a generalist pool that can rapidly adapt to many different specialized niches.  The article is still groping for an answer.  It's pretty obvious from a quick peek at global culture, though.  Where animals are limited to biological adaptations, which are slow, humans can use technological and behavioral ones, which can move much faster.  We see a little behavioral adaptation in animals but they are largely restricted to biology.  Humans can use intelligence to circumvent  instincts -- not always a long-term advantage, as seen in shift workers, but good for short-term survival.  Then biological adaptation follows along behind, and we see little things like Tibetan resistance to altitude sickness.