The oldest human DNA in Africa helps to reveal the ancient demographic transition.

The analysis of ancient and modern DNA shows that from about 20 thousand years ago, ancient Africans traveled long distances to find spouses in exchange for regional ties.

The same analysis shows that this change occurred at least 50 thousand years ago, after the long journey to find breeding partners in most parts of Africa became the norm. These new findings-thanks to several samples of the oldest human DNA isolated from Africa so far-provide the first genetic support for the previously suspected changes in mating patterns at that time.

The long-distance movement of these newly discovered ancient human groups is helpful to explain the archaeological discoveries of common cultural behaviors such as making stone and bone tools that have appeared more and more in most parts of Africa since about 50 thousand years ago. Mark lipson, an evolutionary geneticist at Harvard Medical School, and his colleagues published a paper in the February 23rd issue of Nature.

The researchers reported that since then, among ancient individuals found in central, eastern and southern sub-Saharan Africa, the gene variation sets have become more and more similar. This shows that this area is a genetic melting pot, and hunter-gatherers migrate between three areas and mate with each other along the way.

The research team said that comparing the DNA of ancient humans with that of hunter-gatherers and herders in the same three regions of Africa today shows that about 20,000 years ago, people usually stopped traveling outside their hometown to find mating partners. Jessica Thompson, a biological archaeologist and research co-author at Yale University, said that at least some people may stay close to their homes, because the last ice age peaked at that time, reducing the number of areas with enough edible plants, animals and other resources needed for survival.

"With tropical Africa coming out of the last ice age, this land is full of many small groups with different local cultural traditions," Thompson said. She suspects that groups with different cultures are more inclined to find spouses from neighboring groups that have more in common with them than immigrants from distant areas.

Today's African hunter-gatherers still follow the local cultural customs, speak the languages of different regions, and look for spouses from nearby groups. About 2000 years ago, the migration of farmers from West Africa to East Africa and South Africa largely eliminated the ancient lineage pattern in today's African DNA. This makes ancient DNA crucial for revealing those lost patterns.

In this new study, scientists extracted ancient DNA from the bones of six people previously excavated in eastern and south-central Africa. It is estimated that these people lived about 18000 to 5000 years ago. These new genetic data were studied together with the published DNA evidence of 28 African hunter gatherers as early as about 8,000 years ago. The researchers were able to retrieve the extra DNA of 15 of them.

The main impetus of this new survey comes from several examples containing the oldest known human DNA in Africa. DNA samples of even older Homo sapiens and their close relatives have been found in Europe and Asia, including Neanderthals about 430,000 years ago (SN: 3/ 14/ 16). The cold conditions there preserve genetic material better than those in tropical Africa. In the Stone Age covered by this new study, only Homo sapiens lived in Africa.

The calculation of genetic variation of three African populations-the hunter-gatherer from southern Africa, the hunter-gatherer from Mbuti in central Africa and the herdsmen and farmers from Dinka in northeast Africa-was used to estimate the ancestral patterns reflected in each ancient DNA sample.

Carina Schlebusch, an evolutionary geneticist at Uppsala University in Sweden, said that the findings of Lipson and his colleagues are consistent with previous studies on DNA in ancient and modern Africa, indicating that mating between large-scale human populations began 200,000 years ago or more (SN: 1/22/20). No one involved in the new research.

Thompson said that in this new study, there is also a hint of a "ghost" population unknown from any fossil, but it contributed to the ancestors of ancient East Africans. She suspects that there are more ancient ghost groups in different parts of Africa (SN: 2/ 12/20).