I found this excerpt today. I think it's interesting in light of some of my thoughts in yesterday's post. The author is Michael Hopkin.

Besides dating our most recent common ancestor, Rohde's team also calculates that in 5,400 BC everyone alive was either an ancestor of all of humanity, or of nobody alive today. The researchers call this the 'identical ancestors' point: the time before which all the family trees of people today are composed of exactly the same individuals.This recent date is not really surprising either, Rohde says. Anyone whose lineage survived for a few generations was likely to have descendants spread all over the world. At the identical ancestors point, then, our ancestors came from every corner of the globe, although those from far afield are unlikely to have made a significant contribution to our genetic make-up.Nonetheless, the results show that we are one big family, Rohde says. As he and his colleagues write: "No matter the languages we speak or the colour of our skin, we share ancestors with those who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who laboured to build the Great Pyramid of Khufu."

See the entire article at: http://www.nature.com/news/2004/040927/pf/040927-10_pf.html