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Genetics: An Evolutionary Mate for 'Eve"? by Boyce Rensberger
About 10 years ago, molecular biologists found evidence in human genes that all people share a common female ancestor, dubbed Eve, who lived in Africa about 200,000 years ago. The claim has been challenged on both genetic and fossil evidence, and it has been supported by a repetition of the same kind of analysis. There is an argument that one would expect all current humans to have one common ancestor based on sampling statistics alone.
Michael F. Hammer, a researcher in molecular evolution at the University of Arizona in Tucson, reported in the Nov. 23 Nature that his analysis of a part of the Y sex chromosome indicates that modern humans descended from a common male ancestor who lived 188,000 years ago. Although the new report does not say where that ancient man, whom some are calling 'Adam,' lived, his age is close enough to Eve's for this kind of work.
Both analyses are based on counting mutations that distinguish a portion of one modern person's DNA from that of others and using a "molecular clock" that assumes the mutations arise at a known, constant rate.
Others, however, dispute the genetic evidence and argue that modern people evolved in many parts of the world as products both of the people already living there and of immigrants.
There is evidence for this contrary view in fossils. In 1992, for exmple, researchers found skulls in China that appeared to blend traits of Homo sapiens and the ancestral species, Homo erectus. The skulls are from hominids who lived nearly 400,000 years ago, suggesting the transition was happening long before "Adam' or "Eve' could have lived.
Confidence in genetic approaches to this problem should also be tempered by a second report in the Nov. 23 Nature. Three British geneticists, led by L. Simon Whitfield of the University of Cambridge, carried out analysis of both mitochondrial DNA and Y chromosome DNA from the same people. The mitochondrial data yielded a time of origin of modern humans between 120,000 and 474,000 years ago. The Y chromosome data indicated the origin was probably between 37,000 and 49,000 years ago.
FIGURE 1: This DNA migration pattern map, created from compiled research on DNA populations around the world, demonstrates that the first Humans originated in Africa about 130-180 thousand years ago. Notes: a) mtDNA macro-lineage L is predominant in Africa, b) mt-DNA macro-lineages M and N are found throughout Eurasia and Australia, c) mtDNA lineages H, I , J, K, T, N, U, V, W and X are predominant in West Eurasia, d) mtDNA lineages A, B, C, D, E, F, G, M, P, Q and Z are predominant in Asia and Oceania, and e) mtDNA lineages A, B, C, D, and X are found in the Americas.