Genes, Languages and Artifacts Yield Insights Into African Prehistory
May 10, 2010
Proceedings of the National Academy of Sciences, authors Laura Scheinfeldt, Sameer Soi and Sarah Tishkoff pulled together recent discoveries about the population history of Africa based on languages, artifacts and DNA. Their paper paints the prehistory of the continent in broad strokes, beginning over 100,000 years ago.(This paper is one of many to come out of In Light of Evolution IV: The Human Condition Sackler Colloquium presented by the National Academy of Sciences in December 2009. Links to other papers from this series can be found here (after this week they should be here.). Podcasts of presentations from the colloquium can be found here.)As these authors note, the genetic data indicating that our species originated in Africa has accrued significantly and convincingly. And we now know that today’s African populations began forming over 50,000 years ago. From among those early populations, a relatively small group of individuals migrated out of Africa to populate Eurasia and Oceania. Within Africa, meanwhile, technological innovation (such as the use of more refined stone tools, and later, iron tools) and the development of today’s language families paralleled the formation of today’s ethnic groups. The combination of archaeological, linguistic and genetic data has revealed that some populations remained relatively isolated from one another for tens of thousands of years, but that interactions between groups, especially within the last 5,000 years, have also shaped the genetic diversity of the continent. For instance, the DNA is very clear in revealing the interactions between migrating agriculturalists and pastoralists and the hunter/gatherers who they encountered.As a result of the rich prehistory outlined in this paper, today’s Africans can trace their ancestry to central and southern Africa, where a few click-speaking Khoe-San peoples continue to subsist through hunting and gathering; to northern Africa, where migrations of Afro-Asiatic speakers from the Middle East to the western coast have been taking place for 14,000 years; to the Sahel region near the equator, where Nilo-Saharan (including Luo) and Afro-Asiatic speakers have traveled back and forth from eastern Sudan to Lake Chad for at least 10,000 years; or to western Africa, where the innovations of agriculture and iron age technology supported the migration of Bantu-speaking peoples to all corners of Sub-Saharan Africa within the last 4,000 years. And, of course, many Africans trace ancestry to multiple corners of Africa and to other continents as well.As one of the authors, geneticist Sarah Tishkoff, noted when I spoke with her recently, “The strength of this paper is the deep integration of the genetics, linguistics, and archaeology.” With this synthesis of 25 years of research in mind, I see the diversity that I observed in Kenya in a continental context. The Maasai-speaking Peace Corps trainer undoubtedly had ancestors 4,000 years ago who lived further north in eastern Africa, and may now have distant cousins whose ancestors migrated to southern Africa with their cattle 2,000 years ago. My fellow teacher who spoke Luo inherited her language, cultural traditions and some DNA from her eastern African Nilo-Saharan ancestors, but, according to this PNAS article, probably also traced quite a bit of ancestry to Bantu-speakers of western Africa. My Bantu-speaking students were descendants of migrants from western Africa, but Arab slavery within the last several hundred years may explain some of the lightness of their skin color. Understanding the prehistory of the people I worked with has led me to appreciate, more than ever, the opportunity I had as a Peace Corps volunteer to know such a diverse set of people.23andMe has supported several initiatives that are contributing to the understanding of genetic diversity within Africa. In fact, 23andMe provided funding for one of the studies (Li et al, 2008) reviewed in this paper, knowing that the study would enable 23andMe to provide richer interpretations of customers’ data. I am looking forward to further discoveries that strengthen our understanding of where we, as a species and as individuals, have come from.