60,000 Years Ago – Lake Mungo (Australia) found mitochondrial DNA (mtDNA) from 10 fossils, including a 60,000 year-old-man. This sequence is so primitive that it raises questions some believed recent African origin for humans showing we may need to rethink how we came to be modern humans, such as multiregionalism, a theory which suggests that people coming from Africa interbred with earlier humans already living in various parts of the Old World, because the leading model “Out of Africa” holds that our ancestors first arose in Africa, then spread throughout the world perhaps 100,000 years ago but it may have been earlier and subsequent later humans mixed with the more primitive humans leading to us.

Though genetic evidence has been the cornerstone of the recent African origins hypothesis, molecular evidence also provides grounds to challenge it. For example, upon reanalysis the molecular evidence indicates that Africa was not the sole source of mtDNA in modern humans. In addition, because both theories propose African origins for the human line, molecular data could be interpreted as evidence supporting the African origins of the genus Homo, rat her than the more recent species Homo sapiens. Both models place ultimate human origins firmly in Africa. Other assumptions made by DNA analysis are problematic. For example, it is assumed that rates of mutation are steady, when in fact they can be notoriously uneven. Another assumption is that mtDNA is not subject to selection, when in fact variants have been implicated in epilepsy and in a disease of the eye.’ Another issue is that DNA is seen as traveling exclusively from Africa, when it is known that, over the past 200,000 years, there has been plenty of movement of humans into Africa as well.

In fact, one study of DNA carried on the Y chromosome (the sex chromosome inherited exclusively in the male line) suggests that DNA on the Y chromosome of some Africans was introduced from Asia, where it originated some 200,000 years ago. Nevertheless, recent work on the Y chromosome by anthropologist and geneticist Spencer Wells traces the human lineage to a single population living in Africa about 60,000 years ago. Despite the seeming conflict, all of these data indicate that gene flow has been an important aspect of human evolutionary history. The multiregional hypothesis and recent African origins hypothesis differ in terms of whether this gene flow occurred over the course of 200,000 or 2 million years.

Since 1997, studies of mitochondriai DNA have not been limited to living people. In that year, mtDNA was extracted from the original German Neanderthal remains, and two other Neanderthals have since been studied. Because the mtDNA of each of these differs substantially from modern Europeans, many have concluded that there can be no Neanderthal ancestry in living humans and that Neanderthals must constitute a separate species that went extinct. But biological anthropologist John Relethford (a specialist in anthropological genetics) points out that these conclusions are premature. For one thing, the average differences are not as great as those seen among living subspecies of the single species of chimpanzee. For an other, differences between populations separated in time by tens of thousands of years tell us nothing about differences between populations contemporaneous with each other. More meaningful would be comparison of the DNA from a late Neanderthal with an early anatomically modern European.

Finally, if we are to reject Neanderthals in the ancestry of modern Europeans because their DNA cannot be detected in their supposed descendants, then we must also reject any connection between a 40,000- to 62,OOO –year old skeleton from Australia (that everyone agrees is anatomically modern) and more recent native Australians. In this case, a mtDNA sequence present in an ancient human seems to have become extinct, in which case we must allow the same possibility for the Neanderthals. In short, it is definitely premature to use genetic evidence to remove from modern human ancestry all populations of archaic Homo sapiens save those of Africa. Not even the Neanderthals can be excluded.

Reference 1, 2