Sussex Adam casts doubt on Eve

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Research just published by Adam Eyre-Walker, Noel Smith and John Maynard Smith, of the Centre for the Study of Evolution in BIOLS, has cast serious doubt on one of the main methods used to trace ancient human lineage. Their findings have led them to question the assumption that mitochondrial DNA (mtDNA) is inherited only in the maternal line.

Mitochondria, the power houses of the cell, have their own DNA and reproduce like bacteria, passing on their genetic material separately from the rest of the cell. Information on the mtDNA has been used to build up evolutionary trees to show how different groups of humans are related, by assuming that variations in mtDNA could only be the result of mutations accumulated in maternal lineages since divergence from a common ancestor, and that similarities indicate close common maternal ancestry. The small amount of variation in the mtDNA of modern humans has led to the widely-held view that we have a common female ancestor (Eve?) who lived in Africa about 200,00 years ago

Using human mtDNA sequences, as well as material from a number of apes, the Sussex team have constructed a phylogenetic tree and found genetic similarities where they should not be, between diverged members of the tree, at about 8-10 times the frequency that would be expected from random mutation. The best explanation for this is that there has been sexual recombination of the DNA and that this has involved mtDNA from the male parent. Recent research has shown that mitochondria from the sperm can enter the egg and that they contain the necessary enzymes. How long these mitochondria survive is not known, but it now seems that there must be at least some fusion and recombination between mitochondria.

In the same edition of the Proceedings of the Royal Society of London, B, another group of researchers has come to a similar conclusion on the basis of work on the mtDNA in a human population of an island in Melanesia. All this has far-reaching repercussions and may lead to a reassessment of some lineages. According to Adam, data will be harder to understand and the variation that we see may be older than we thought. So may Eve.