Amsterdam, Netherlands ? Dutch researchers theorize that an AIDS-like epidemic wiped out huge numbers of chimpanzees 2 million years ago, leaving modern chimps with resistance to the AIDS virus and its variants.

If true, the hypothesis would explain why chimps, which share more than 98 percent of their DNA with humans, don’t develop AIDS.

The theory stems from a study of DNA in 35 chimps conducted by the Biomedical Primate Research Center in the Netherlands. The chimps in the study shared an unusually uniform cluster of genes in the area that controls their immune systems’ defenses against disease.

“Chimps show more genetic variation than humans in all areas with this one exception, which is seriously condensed,” said Dr. Ronald Bontrop, who led a Dutch team that worked with statisticians from the University of California.

The findings will be published in the coming issue of the Proceedings of the National Academy of the Sciences of the United States. An online version was already available on the academy’s Web site.

Bontrop told The Associated Press that the chimp’s lack of genetic diversity, which was found in genes related to the immune system’s defense against disease, suggested that a lethal sickness attacked chimps in the distant past.

This unknown disease would have wiped out all or almost all chimps that didn’t have the right immune system genes to fend it off, leaving the survivors with a uniform set.

This, combined with the knowledge that modern chimps were largely immune to the AIDS virus and its simian variants, pointed toward an AIDS-like disease as the culprit.

Scientists believe that HIV, the virus that causes AIDS, originated in apes or monkeys and was transferred or mutated its way into the human population about 50 years ago.