Carl Zimmer in his always excellent blog, The Loom:
Trace your geneology back 25 million years, and you’ll meet long-tailed monkey-like primates living in trees. Those primates were not just the ancestors of ourselves, but of all the other apes–chimpanzees, bonobos, gorillas, orangutans, and gibbons–along with the monkeys of the Eastern Hemisphere, such as baboons and langurs. By comparing ourselves to these other primates, scientists can get clues to our evolution over the past 25 million years. Until now, most of those clues have come from fossils and studies on the behavior and physiology of apes and monkeys. But in the past few years scientists have begun to pore over a new record: the one that is inscribed in our genome and the genomes of other apes and monkeys.
The first draft of the human genome was published in 2000, and in 2005 came the genome of the chimpanzee–our closest living relative. Scientists compared the two genomes to get a sense of what the genome of our common ancestor looked like, and how the genomes of both species have changed over the past few million years. (I wrote about the first wave of chimp/human studies here). One of the biggest surprises came when one team of researchers concluded that the ancestors of chimpanzees and humans interbred for over a million years, producing hybrid humanzees.