Chimpanzees are the closest living relatives to humans, sharing a surprising 98.8 percent of our DNA. How can we be so similar—and yet so different? To explore this question, geneticists from the Evan Eichler lab at the University of Washington and the Howard Hughes Medical Institute in Seattle compared gene maps of ourselves and our primate relatives. They confirmed previous findings that humans, chimpanzees and gorillas have a surprisingly large number of genetic mutations called gene duplications. These mutations occur when an organism makes extra copies of genes or segments of genes during cell division. When the DNA is passed to the next generation, the gene duplications accumulate in the genome of the species.

The researchers were able to trace that bursts of gene duplication activity occurred just before the human, chimpanzee, and gorilla lineages diverged, and again just before the chimpanzee and human lineages diverged. These kinds of mutations may have caused certain primate ancestors to have such different traits that some evolved into new species.

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