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Mitochondrial DNA testing shows that all humans descended from a founding group in East Africa around 140,000 years ago. Haplogroups L1, L2, and L3 spread across Africa, with L3 crossing the Red Sea into Yemen and eventually colonizing Europe, Asia, and Australia. A discrete migration occurred at the Bering land bridge, and humans have since colonized Pacific islands.
The current mitochondrial DNA test has given us a lot of valuable information about the ancient history of mankind. His most important contribution was testing the theory out of Africa, also known as the recent single origin hypothesis. The out of Africa theory states that all of humanity is descended from a founding group that originated in East Africa, probably somewhere around modern-day Tanzania. Its main competitor, now largely rejected, is the multiple origin theory, a group of related claims that humanity originated separately in different areas, from different pre-human apes, and subsequently interbred.
The type of DNA test most frequently used to study the origins of mankind is the mtDNA test, also known as mitochondrial DNA. Mitochondrial DNA is made up of small fragments of DNA found in the mitochondria (power plants) of cells. It is passed on matrilineally, which means you get your mtDNA from your mother. There is another type of DNA, Y chromosomal DNA, which is passed down through the patrilineal line. Different forms of DNA testing are associated with both. The reason these two types of DNA are particularly useful for studying early human migrations is that they are the only DNA that is not constantly shuffled due to genetic recombination.
The date that the common mtDNA ancestor of all living humans, known as “Mitochondrial Eve” was alive, is given by DNA testing as approximately 140,000 years ago. This is not the most recent common ancestor of all humans, who lived much more recently, just 2,000 to 5,000 years ago, but the most recent common ancestor across the mtDNA line. By studying how DNA haplogroups branch off from mitochondrial Eve by testing the mtDNA of thousands of people around the world, scientists can get a rough picture of how early migration patterns fared.
According to DNA testing, modern humans originated about 140,000 years ago in East Africa, where they have lived exclusively for several tens of thousands of years. This corresponds to haplogroup L1. Between 84,000 and 107,000 years ago, humans spread across the rest of Africa, giving rise to haplogroups L2 and L3, which headed west and northeast, respectively. Most modern African Americans are members of haplogroup L2.
About 72,000 years ago, a small group of haplogroup L3, probably numbering only 100-200 individuals, crossed the Red Sea into present-day Yemen. These are the ancestors of all humans outside of Africa. They spread to Europe, Asia and Australia, where they arrived about 50,000 years ago. About 12,000 years ago, a similar discrete migration occurred at the Bering land bridge in the Americas. This group are the direct ancestors of all modern natives of North and South America. More recently, humans have colonized Pacific islands from launch points in Southeast Asia. Anthropological and archaeological evidence largely supports this view of early human migration.
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