By LEE BOWMAN
Scripps Howard News Service
August 31, 2005
Scientists estimate that human and chimp ancestors went down different evolutionary branches about 6 million years ago, and that the genetic code for everything from language and social interactions to walking upright evolved in humans since then.
Looked at another way, there's only about one-tenth of 1 percent difference between the genes of any one person and another human, which is 10 times less than the difference between humans and chimps, the researchers said.
By comparing the genetic differences in detail, "we can see what makes us human, what types of genes and what types of changes, led to the emergence of a truly new species," said Dr. Robert Waterston, chair of the Department of Genome Sciences at the University of Washington School of Medicine in Seattle. He is senior author of one comparative study published Thursday in the journal Nature, which also published several related papers.
The project, carried out by an international team of 67 researchers who are part of the Chimp Sequencing and Analysis Consortium, took more than two years and cost between $20 million and $30 million. The National Human Genome Research Institute sponsored the work.
"As our closest living evolutionary relatives, chimpanzees are especially suited to teach us about ourselves," Waterston said. Chimps are immune to some infections that humans are not, they don't get Alzheimer's disease and rarely get cancer, but seem to share genetic susceptibility with humans for diseases like diabetes.
The DNA used to produce the chimp-gene map came from the blood of a male chimpanzee named Clint at the Yerkes National Primate Research Center in Atlanta. Clint died last year from heart failure at the relatively young age of 24, but cell lines from his tissue have been preserved.
While there's only been a 1 percent change in the shared genes of chimps and humans in 6 million years, each species has also either added or dropped another 1.5 percent of their genes, the study found, so they are actually only 96 percent genetically the same.
Other researchers note that there's been a lot of duplication of large segments of these new genes, many of which might be significant to how humans have evolved. "Now, we need to learn the role of these duplication events in species evolution and disease," Waterston said.
Already, researchers have found that three key genes involved in response to inflammation are missing from the chimp-gene map, which may explain some of the known differences in how the two species respond to disease. On the other hand, humans appear to have lost the function of a gene that produces an enzyme that may help protect other animals against Alzheimer's disease.
Tarjei Mikkelsen, a graduate student-researcher at the Broad Institute of the Massachusetts Institute of Technology and Harvard University who was the lead author of the study, said it appears some classes of genes have been evolving more rapidly in humans than in chimps.
"The class of genes that changes the fastest are genes that control other genes, which may help explain why the human shape and body plan evolved so fast," Mikkelsen said.
Dr. Francis Collins, director of the federal Genome Institute, noted that the father of evolutionary theory, Charles Darwin, was the first to recognize that humans and chimps were evolutionary cousins, although he didn't know about the intricate biological mechanics that make us so close.
While the genetic comparison "is certainly an elegant way to document evolution," Collins said the findings may not entirely explain what it takes to be human.
"It will tell what changes in the central nervous system were needed to be able to have language, to be able to sequence genomes, for that matter," he said. "But it may very well not tell us how we came to be able to tell the difference between right and wrong or how the human spirit emerged."
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