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Scoping Out Signs of Human Evolution
20 December 2005 (All day)
Who says humans aren't the result of Darwinian evolution? This week, researchers report identifying some 1800 genes that appear to have been the target of natural selection. Some of the genes may be important in understanding the genetics behind disease as well as the evolution of the human brain.
The sequencing of the human genome (ScienceNOW, 14 April 2003:) gave scientists major new insights into what makes us human: Although we share more than 98% of our genetic code with the chimpanzee, natural selection has turned us into a very different animal than the chimps, from whom our hominid ancestors split evolutionarily some 6 million years ago (ScienceNOW, 31 August). While the Human Genome Project revealed much about our common humanity, recently scientists have begun to learn a lot about human evolution from the small genetic differences that set us apart.
Now a team of scientists at the University of California, Irvine, has used a new computational approach--the "linkage disequilibrium decay" test--to search for signs of selection over the entire human genome. As a rule, the greater the linkage disequilibrium associated with a gene, the more likely that the gene has been under recent selection. Harnessing data from two existing databases of human diversity, the team found some 1800 genes that appeared to have been under selection during the last 10,000 to 50,000 years. According to team leader and genome researcher Robert Moyzis, this is between 10 and 100 times greater than the number found in previous studies (Science, 8 July, p. 234).
The genes belong to several biologically important categories, including genes important in defense against disease, controlling the cell cycle, protein metabolism, and nervous system functioning, the researchers report online this week in Proceedings of the National Academy of Sciences. One of the newly spotted genes, ASPM, was recently linked to brain evolution by a team from the University of Chicago (Science, 9 September, p. 1662).
David Altshuler, a human geneticist at Massachusetts General Hospital in Boston and the Broad Institute of Harvard University and the Massachusetts Institute of Technology, says that the study's findings are consistent with natural selection but cautions that there could be other explanations. Nevertheless, says genome researcher Pardis Sabeti, also of the Broad Institute, the research is "well executed and has good insights." Sabeti adds, "The study of natural selection in humans is incredibly active right now, and this paper is part of a wide array of exciting new genome-wide surveys."