We now know that all humans living today had ancestors who came from Africa about 200 thousand years ago. This realization was gradual, emerging as we made more fossil discoveries and refined the story of having ancestry from one place, as opposed to multiple ancestries spread around the world. However, it was a DNA study conducted in the 1980s that solidified this conclusion.
This study was one of the first in genetics to involve mitochondrial DNA, which constitutes only approximately 1/200,000th of the genome and is passed down along the maternal line from mother to daughter to granddaughter. In 1987, Allan Wilson and his colleagues sequenced a few hundred letters of mitochondrial DNA from diverse people around the world. By comparing the mutations that differed among these sequences, they could reconstruct a family tree of maternal relationships.
The researchers discovered that the oldest branch of the human family tree, which separated first from the main trunk, is only found in people of sub-Saharan African descent. This suggests that the ancestors of modern humans originated in Africa. The study examined mtDNA from various populations and found the highest genetic diversity—a significant indicator of a species’ origin—in African populations. This diversity decreases with increasing distance from Africa, supporting the theory that modern humans left Africa and gradually spread to other parts of the world.
The identification of Mitochondrial Eve was a major piece of evidence for the “Out of Africa” theory of human evolution, which posits that modern humans (Homo sapiens) first evolved in Africa and then spread to other continents, replacing other early human species such as Neanderthals and Homo erectus. This discovery not only highlighted the commonality of all human beings but also sparked widespread interest and further research into human evolutionary history.
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