Africa's hidden people hold the keys to the past

I mentioned this in passing on my post on ASHG 2012, but it seems useful to make explicit. For the past few years there has been word of research pointing to connections between the Khoisan and the Cushitic people of Ethiopia. To a great extent in the paper which is forthcoming there is the likely answer to the question of who lived in East Africa before the Bantu, and before the most recent back-migration of West Eurasians. On one level I'm confused as to why this has to be something of a mystery, because the most recent genetic evidence suggests a admixture on the order of 2-3,000 years before the past.* If the admixture was so recent we should find many of the "first people," no? As it is, we don't. I think these groups, and perhaps the Sandawe, are the closest we'll get. Publication is imminent at this point ...