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The Mitochondrial Eve
| Article
# : |
13469 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1987 |
4,386 Words |
| Author
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Rebecca L. Cann
Rebecca L. Cann is assistant professor of genetics at the
University of Hawaii. |
Most urban North Americans are a bit like West African Pygmies. They have neither the interest nor the ability to trace their kinship back further than 3 generations. In contrast, some Samoans can produce pedigrees 20 generations long. History may count for so little to so many, but what about the future? Demographers estimate that an American male probably has less than a 20 percent chance that a direct descendant with the same last name will be alive 250 years from now. Human families just don't persist very long.
If most lineages that we can actually identify ultimately die out, how is it possible that our species has survived for thousands of years? Recent research suggests that we are all directly linked through maternal genes to a nameless, faceless great-grandmother 200,000 years old, and scientists must now grapple with the implications of this deep penetration into human kinship. Astonishing as it may seem, molecular anthropology shows that all people alive today trace some of their genes to a single woman who was probably from Africa. This female may be the only common link in our species. She contributed a set of genes that has been passed on only by women, and through those genes, we are uncovering areas of the past that have been hidden from us by history, culture, and our own eyes.
Scientific advances rarely proceed in straight lines, and the study of human evolution has been no exception. Yet the traditional portrayal of the fossil evidence of our ancestry gives the impression that scientists have reliably mapped the evolution of humans. It seems that once some messiness was sorted out 5 million years ago, there was a smooth steady development of the line. Although new molecular refinements provide counterevidence, human evolution is still diagrammed in a series of simple, ancestor-descendant relationships. Dioramas in a natural history museum can be counted on to show some primitive ape-human (Australopithecus) merging into some early species of our own genus, Homo. Then Homo erectus evolves into Homo sapiens, along with mortgages, star wars, and ice cream. Such schemes imply a genetic continuity in space and time that contains more fantasy than Spiderman's best escapades. Accurate reconstructions of human phylogeny depend on the successful mating of two individuals, a process we can only infer for the past. A Homo erectus couple never gave birth to a Homo sapiens baby, so how did modern humans evolve? Contrary to the smooth development shown in the dioramas, we cannot yet explain these transitions.
All scientists make assumptions about their systems. Paleontologists ask us to believe
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