Genome-wide analyses of 41 ancient sub-Saharan Africans answer questions left murky by archaeological records about the origins of the people who introduced food production--first herding and then farming--into East Africa over the past 5,000 years.
Science, embargoed until 2 p.m. Eastern, Thursday, May 30
Analyses suggest a multi-stage model for the spread of food production into the region known today as Kenya and Tanzania.
The introduction of herding is linked with movement into the region of two distinct groups from northeast Africa, who mixed with each other and with local hunter-gatherers.
Starting 1,200 years ago, additional people from northeastern and western Africa moved into the region and contributed genetic profiles similar to many groups living in East Africa today.
Despite great variety in pottery styles, tool materials and burial practices, Stone Age herders across East Africa were found to have closely related genomes, highlighting how cultural differences do not always map to genetic ancestry differences.
Genes for lactose digestion in adulthood were rare in the first East African herders, suggesting that as in Europe, the rise in frequency of this trait lagged behind the widespread use of cow's milk by thousands of years.
The international study more than doubles the number of ancient genomes analyzed from sub-Saharan Africa.
The current study involved close and fully equal collaboration between archaeologists and geneticists.
Partnerships included African scientists and curators, particularly from the National Museum of Kenya, and also Henry Louis Gates, Jr. at Harvard.
The study formed the basis for the development of ethical guidelines and preservation protocols for sampling ancient DNA, published here.
Two study authors, both archaeologists, wrote an article about the work while it was ongoing and have a new commentary that will appear in The Conversation at the same time as the paper.
Authorship and DOI
Senior author is David Reich of Harvard Medical School. Co-first authors are Mary Prendergast of Saint Louis University-Madrid Campus (Spain), Mark Lipson of HMS and Elizabeth Sawchuk of Stony Brook University. http://dx.