Mitochondrial DNA, or mtDNA for short, is the DNA found in mitochondria, the part of your body’s cells that turns food back into life. Mitochondrial DNA is different than nuclear DNA (nuDNA), the kind at the centre of your cells, in at least three ways:
- All of it comes from your mother, none of it from your father.
- It is very short, making only 16 different proteins.
- It has no way to proofread itself to check for copy errors.
The last one means that mtDNA mutates or changes a hundred times faster than nuclear DNA. Most mutations are harmful and do not get passed on. But some are harmless and a few are even helpful. In mtDNA a harmless mutation takes place about once every 3,000 years.
In the late 1980s geneticist Allan Wilson tested the mtDNA of 137 people from different parts of the world. With that he built a family tree of mankind by assuming that those with fewer mutations between them were more closely related.
He was able to tell not only how man spread across the earth, but when (pictured above according to the latest numbers). By assuming one mutation every 3,000 years, mtDNA becomes like a clock that keeps time over tens of thousands of years.
In the 1980s many scientists believed in multiregional evolution: that humans, Homo sapiens, came from earlier manlike creatures not in one particular place but slowly all over the world. So the Chinese, for example, came from Peking Man (Homo erectus).
Wilson’s work overturned that. He showed that humans started in just one place: East Africa. From there they spread slowly across Africa and then across the whole earth – at the speed of one mile (1.6 km) a generation. This is called the Out of Africa hypothesis.
When humans got to Europe they did not mate with the earlier Neanderthals: they either wiped them out or pushed them aside. There is no known mtDNA from Neanderthals in any one alive. The Neanderthal, Peking Man and all the rest were dead ends, not our ancestors.
By looking at people’s mtDNA and working backwards you can tell that everyone alive today came from a single woman who lived in Africa about 200,000 years ago: Mitochondrial Eve.
A branch of the human family tree where everyone has roughly the same mtDNA is called a haplogroup. They are given letters: L, N, M, X, etc. The dark-skinned people in southern India, Australia, New Guinea and Melanesia, for example, belong to haplogroup M.
Most black Africans belong to haplogroup L, the same as Eve herself. There are seven main branches of it within Africa, named L0 through L6.
About half the people in Europe belong to haplogroup H. Its Eve has been called Helena. She lived in south-western France 20,000 years ago. By 28,000 years ago her ancestors were already in Europe. That is not good guesswork but a fact: we have the remains of a person called Paglicci 23 who lived in Italy 28,000 years ago that we can date and test.
– Abagond, 2010, 2016.
Update (2016): It is now known that at least some people from outside of Africa have some Neanderthal genes.