An equally valid hypothesis is that there was no environmental change, but that in an otherwise genetically diverse population one small group gained a genetic competitive advantage over other proto-humans and began to multiply wildly, killing off or starving out the rest of the gene pool. It would be interesting to compare the age of the various genes for cognitive ability, speech and socialization to see if any date to the period where these choke points occurred.

I would like to think it was a gene that supported empathy or cooperation that enabled them to out-compete their neighbors, but rather I suspect that a genetic disposition to xenophobia is a more likely culprit...

This plainly shows that our real enemies are all those creatures presently on the endangered species list. In the name of all that is holy, I call on you all to go out and hunt down the remaining grey wolves and pandas before they devour us all.

Hey, calm down Matt4077. Stop yelling at the nice slashdotters and I will give you a piece of candy.

.... Of course, there are ~10e6 of days travel just between here and Mars, so those Altarian dollars really start to add up....