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Humans did come out of Africa, says DNA
December 07, 2000
Extract: Nature ScienceThe genetic material in our chromosomes is a combination of genes from our parents. But each cell also contains structures called mitochondria, and these house DNA that is independent of that found in chromosomes.
Mitochondrial DNA (mtDNA) gives researchers a window into history because it is only transmitted along the female line. There is no mixing between generations, and the DNA sequence only changes as a result of random mutations or copying errors. If these mutations appear at a fairly constant rate, then comparing the mitochondrial DNA of two populations reveals roughly when they had a common ancestor.
This approach is not new, but in the past researchers have concentrated on only 7% of the total mitochondrial DNA sequence, known as the control regions. The mutation rate for these regions might be different from the rest of the sequence, so Gyllensten and co-workers sequenced the entire mitochondrial DNA of 53 people from diverse ethnic backgrounds. They excluded any parts of the DNA that mutated unusually quickly, then compared the data to produce a sort of human family tree.
They discovered that the most recent common ancestor of everyone in the sample group lived in Africa 171,500 ± 50,000 years ago. They also found a significant branch in the tree that separates most Africans from non-Africans. This genetic divide probably represents an exodus of people from Africa that took place 52,000 ± 27,500 years ago.
This evidence favouring the ‘recent African origin’ theory of human evolution is compelling, but the researchers hope for better data in the near future. "Mitochondrial DNA is only one locus, and only reflects the genetic history of females," they write. "With the human genome project nearing fruition, the ease by which such data may be generated will increase, providing us with an evermore detailed understanding of our genetic history."
Nature / December 07, 2000
Human evolution: A start for population genomics
S. BLAIR HEDGES
The most thorough analysis yet of the divergence of sequences in human mitochondrial DNA has been carried out. The results support the view that modern humans originated in Africa.
Nature 408, 652-653 (7 December 2000)Humans did come out of Africa, says DNA
Thursday 7 December 2000 The DNA of living humans is revealing when and where we evolved, reports Jeremy Thomson. (7 December 2000)