Decoded chimpanzee genome shows what makes us different from chimps

Scientists said yesterday that they have determined the precise order of the 3 billion bits of genetic code that carry the instructions for making a chimpanzee, humankind's closest cousin.

The fresh unraveling of chimpanzee DNA allows an unprecedented gene-to-gene comparison with the human genome, mapped in 2001, and makes plain the evolutionary processes through which chimps and humans arose from a common ancestor about 6 million years ago.

By placing the two codes alongside each other, scientists identified all 40 million molecular changes that today separate the two species and pinpointed the mere 250,000 that seem most responsible for the difference between chimpness and humanness, reports Washington Post.

According to Newsday, Scientists said the number of genetic differences between chimps and humans is 10 times greater than the variation seen between any two humans. But underscoring the close evolutionary heritage between the two species, that genetic gulf is still 10 times narrower than the one observed between the mouse and rat genomes.

Since our evolutionary divergence from a common ancestor about six million years ago, both humans and chimpanzees have accumulated more changes than other mammals in genes linked to the production of sperm, the perception of sound and the transmission of nerve signals, among others.

Dr. Christopher A. Walsh, a neurology professor at Harvard Medical School, said the studies showed that a small number of changes were enough, demonstrating the power of evolution to respond to circumstances.

"You don't have to wait for 100 different changes to occur simultaneously for something to happen," Walsh said.

Scientists found six areas of the human genome that were overcome with mutations during a period of rapid and widespread change, an event called a "selective sweep." These areas are remarkably similar, indicating that the changes occurred roughly within the last 200,000 years.

As an example, Landers cited the emergence of the gene for digesting lactose, which allows humans to drink milk from animals. The mutation would confer an evolutionary advantage, helping it to spread quickly and maintain its original form, informs LA Times.