Biologists have long held that the genes of chimps and humans are about 98.5 percent identical.
But Roy Britten, a biologist at the California Institute of Technology, said in a study published this week that a new way of comparing the genes shows that the human and chimp genetic similarity is only about 95 percent.
Britten based this on a computer program that compared 780,000 of the 3 billion base pairs in the human DNA helix with those of the chimp. He found more mismatches than earlier researchers had, and concluded that at least 3.9 percent of the DNA bases were different.
This led him to conclude that there is a fundamental genetic difference between the species of about 5 percent.
Britten said the new study, appearing this week in the Proceedings of the National Academy of Sciences, should help biologists figure out how species branched out from each other over the course of evolution.
"A large number of these 5 percent of variations are relatively unimportant," he said in a statement. The next step is to compare how the genes are regulated in the two species and find out where all the genetic differences are located in the DNA, he said.