DNA

Clint, a chimpanzee whose DNA was used to sequence the chimpanzee genome, is seen in a handout photo from Yerkes National Primate Research Center. Scientists have deciphered the DNA of the chimpanzee, the closest living relative of humankind. (AP Photo/Yerkes National Primate Research Center)

NEW YORK --  Scientists have deciphered the DNA of the chimpanzee, the closest living relative of humankind, and made comprehensive comparisons with the human genetic blueprint. It's a step toward finding a biological answer to a key question: What makes us human?

There are no firm answers yet about how humans picked up key traits such as walking upright and developing complex language. But the work has produced a long list of DNA differences with the chimp and some hints about which ones might be crucial.

We've got the catalog, now we just have to figure it out, said Dr. Robert Waterston of the University of Washington School of Medicine in Seattle. It's not going to be one gene. It's going to be an accumulation of changes.

He is senior author of one of several related papers appearing in Thursday's issue of the journal Nature and being published online Thursday by the journal Science.

In the papers, Waterston presents a draft of the newly deciphered sequence of the chimp genome, in which an international team of researchers identified virtually all the roughly 3 billion building blocks of chimp DNA.

It's a huge deal, said Dr. Francis Collins, director of the National Human Genome Research Institute, which provided some support for the project. We now have the instruction book of our closest relative.

He said the work will help scientists analyze human DNA for roots of disease.

While the DNA comparisons don't firmly identify specific differences that played a big role in producing humans, they do indicate promising areas, said Bruce Lahn, who studies human evolution genetics at the University of Chicago but didn't participate in the project. Lahn said the research refutes a few previous ideas while providing new and better evidence for others.

Humans and chimps have evolved separately since splitting from a common ancestor about 6 million years ago, and their DNA remains highly similar _ about 96 percent to almost 99 percent identical, depending on how the comparison is made.

Still, the number of genetic differences between a human and a chimp is about 10 times more than between any two humans, the federal genome institute says. It's the differences _ some 40 million _ that attract the attention of scientists.

Waterston and colleagues, for example, looked for genes that apparently have changed more quickly in humans than in chimps or rodents, indicating they might have been particularly important in human evolution. They found evidence of rapid change in some genes that regulate the activity of other genes, telling them when and in what tissues to become active, for example.

It would make sense that changes in these regulatory genes could have a broad impact on how organisms develop, playing a key role in human evolution, Waterston said.

With help from the chimp DNA, his team also uncovered several regions of human DNA that apparently contain beneficial genetic changes that spread rapidly among humans within the past 250,000 years. One area contains a gene called FOXP2, which previous work has suggested is involved in acquiring speech.

Svante Paabo of the Max Planck institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues report in the Science paper that genes active in the brain have changed more in the human lineage than in the chimp lineage. That wasn't the case for genes from other organs such as the heart and liver.

In a telephone interview, Paabo said that in general, I'm still sort of taken aback by how similar humans and chimps are in their DNA. I'm still amazed, when I see how special humans are and how we have taken over this planet, that we don't find stronger evidence for a huge difference in our genomes.

He said he believes the key differences between the species will prove to be subtle things such as patterns of gene activity and how proteins interact.

In fact, Waterston and co-authors said they hoped documenting the overall similarity of chimp and human genomes will encourage action to save chimps and other great apes in the wild:

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.

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On the Net:

Nature magazine: http://www.nature.com

Science magazine: http://www.sciencemag.org