Scientists have compared the genetic blueprints of humans and chimpanzees for the first time and discovered thousands of genes that are virtually identical in both species -- confirming the long-held belief that chimps are humanity's closest living relatives.

But more than that, the scientists said, the landmark finding promises important advances in human disease research and supports many of the insights on evolution proposed by Charles Darwin 150 years ago.

"Sequencing the chimp genome is a historic achievement that is destined to lead to many more exciting discoveries with implications for human health," declared Dr. Francis Collins, leader of the government-sponsored project that produced the first draft sequence of the human genome five years ago and a complete human DNA map only last year.

The 67 scientists from five nations leading the chimp genome project are reporting their results today in a series of eight papers published in the journal Nature. Researchers leading the project described their work Wednesday at a Washington press conference.

Lining up 3 billion bits of genetic code, the chimp genome team determined that 96 percent of the protein-coding genes in both chimps and humans were identical, while in some stretches of DNA where genes either regulate other genes or whose function is unknown, as much as 99 percent of the genetic material in both is identical, the scientists concluded.

Even more significant, they said, are the many gene sequences that remain different between the primates known as Homo sapiens sapiens and our close cousins, the chimp species called Pan troglodytes. Among the 35 million tiny bits of DNA in the human genome that differ from chimps, for example, lie clues to the manner in which natural selection -- the basic machinery of evolution -- has given humans the unique ability to walk upright, to use language and to think, reason and develop complex tools, said Dr. Robert Waterston of the University of Washington, the senior author of the principal comparative study. Mutations in the DNA of many of those genes may well have occurred within the past 250,000 years, and because they proved so beneficial, they spread rapidly throughout the human population, he said.

In both chimps and humans, nearly 25,000 genes carry the genetic code for creating all the proteins that make up their bodies and brains, while thousands more regulate the machinery. All those genes are built from some 3 billion chemical units of DNA called base pairs, and it took more than four years for the researchers to tease out the similarities and differences that define the two species.

Scientists have estimated from the fossil record that the evolutionary lineages of humans and the great apes like chimpanzees diverged from a common ancestor between 5 and 8 million years ago, and the chimp genome team believes the split must have occurred roughly 6 million years ago.

Over all the millennia since that time, relatively few changes have occurred in the chimp genome, Waterston and his colleagues said. That has placed humans at a disadvantage in some areas. Chimps, for example, have been able to resist many infections like HIV and AIDS, and they don't get malaria, diabetes, cancer or Alzheimer's -- while humans can succumb to all these maladies.

Yet, as Collins noted, "we have peeked into evolution's lab," and it's just these differences that could provide a new understanding of those diseases as researchers pursue their quest for prevention and treatment in new directions.

Some classes of genes, however, appear to have changed relatively rapidly in both chimps and humans, the scientists say. They include genes involved in hearing, transmission of nerve signals and production of sperm.

The team members working on the pathbreaking project in Israel, Italy, Germany and Spain as well as the United States obtained their genetic material from cell lines extracted from a chimpanzee named Clint, who died from heart failure last year at the age of 24 and had lived all his life at the Yerkes Primate Research Center in suburban Atlanta.

Like many other ape species, Africa's chimpanzee population is seriously threatened, and Waterston and his colleagues said they hoped that Clint's role in giving scientists proof that chimps and humans were so similar would encourage humans to save their close relatives.

"We hope that elaborating how few differences separate our species will broaden recognition of our duty to these extraordinary primates that stand as our siblings in the family of life," Waterston said.