Humans and chimpanzees share an almost perfectly identical genetic inheritance, scientists report Thursday in a landmark comparison that they call an "elegant confirmation" of naturalist Charles Darwin's theory of evolution.
The research is the first comprehensive analysis of the human and chimp genomes. The 3 billion genetic letters in the two genetic blueprints are 96 percent identical with just 40 million differences, the researchers report in the journal Nature.
By delving more deeply into those differences, researchers hope to discover new explanations of why humans are susceptible to certain diseases, why our evolutionary paths diverged from ancestral chimps 6 million years ago, and on an even more basic level, what makes us human.
"We can peek into evolution's lab notebook and see what went on there," says Francis Collins, director of the National Human Genome Research Institute. Project costs ranged from $20 million to $30 million, he said.
The analysis offers clues to the cause of diseases such as Alzheimer's and to why humans may be more susceptible to some infections. "Evolutionary analysis is a handmaiden to human medicine," says Eric Lander, of the Broad Institute of the Massachusetts Institute of Technology and Harvard.
In a discovery that may offer an insight into Alzheimer's disease, researchers found mutations that inactivate the human version of the gene "caspase-12," which limits cells' life span. Those mutations weren't found in chimps, which aren't as susceptible to Alzheimer's. Knocking out caspase-12 in mice causes Alzheimer's-like deposits to form in their brains.
Researchers also identified mutations in the human genome that were so beneficial for survival they quickly became "the norm throughout humanity." And they found that the Y-chromosome, which confers maleness, has remained more stable in humans than in chimps.
"Reading these two genomes side by side, it's amazing to see the evolutionary changes that are occurring," says Robert Waterston of the University of Washington. "I couldn't imagine Darwin looking for stronger confirmation of his theories."