Speaking of which, did you check out:
Human line 'nearly split in two' and When humans faced extinction?
I'd be interested in your thoughts.
I'd not read those specific articles, but am familiar with the work.
From a scientific point-of-view the last one - when humans faced extinction - is the best supported evidence wise. Long story short, we know from direct measurements how quickly mitochondrial DNA mutates, we know how variable it is in todays humans (very little), and we've identified several mitochondrial "lines" which date back to the same period.
The only viable conclusion is that there was an event which resulted in a small number of earlier humans passing their mitochondria (and therefore genes) on. Or, in other words, we almost died off, and everyone today is an ancestor of a small group that made it.
The first paper is a little more dubious; basically it claims that (in Africans) there are two major "lines" of mitochondria, suggesting that at some point there were two distinct groups of humans that later mixed. The only problem is, as described in the article, that there are other explanations which can account for the apparent presence of two main lineages.
Likewise, they only looked at African mitochondrial DNA, meaning there could be other distinct groups which aren't accounted for in this study. Lastly, on the scale of things, mitochondria evolve quickly, compared to the rest of our genes, so even though it looks like we may have been heading towards a split in the species its quite possible our genomic DNA never diverged all that much. If it had, you'd expect to see evidence of that today, and we don't.
Bryan
