DNA Shows Human-Ape Links, Differences

More similarities than differences?

hide captionMore similarities than differences?

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Scientists say a rough draft of the chimpanzee genome shows that Darwin was right when he said that African great apes and humans share common ancestors. The genome also shows key areas where humans and chimps differ. And researchers believe it will help them understand how subtle genetic changes have made human brains very different from chimp brains.

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A new genetic analysis confirmed something that Charles Darwin suggested more than a century ago: Humans and chimps have a lot in common. This analysis comes from the first detailed reading of the chimpanzee genome. Scientists say studying the genes of an ape will help them understand what it means to be human. NPR's Jon Hamilton reports.

JON HAMILTON reporting:

Scientists unveiled the chimp genome at a press conference today. Eric Lander of MIT and the Broad Institute says the new genetic sequence makes one thing very clear.

Mr. ERIC LANDER (MIT; Broad Institute): Humans and chimps are remarkably similar. If we line up the DNA letters, at the positions where they can be aligned--were 99 percent identical, only one letter difference out of a hundred between humans and chimps.

HAMILTON: That still leaves 40 million differences, though that's not a lot in genetic terms. Lander says a mouse and a rat are about 10 times more different genetically than a chimp and a human.

Mr. LANDER: Charles Darwin couldn't have asked for a more spectacular confirmation of his very controversial prediction back in 1871 that the great apes were our closest relatives.

HAMILTON: It took more than 60 researchers to complete the genetic sequence of the chimpanzee. They used DNA from an ape named Clint. Unfortunately, Clint died of a heart problem before his DNA could make him famous. He was 24.

Scientists have been waiting eagerly for the chimpanzee sequence. An early draft showed how humans and chimps are alike, but Lander says this version offers something even more valuable.

Mr. LANDER: For the first time we've now laid out on the table the whole menu of genetic differences between humans and chimps. And it's an open invitation to scientists studying medicine to be able to home in on those unique aspects of the human species and understand how they give us our unique physiology, our unique responses to disease, our unique susceptibilities and some of our unique behavioral traits.

HAMILTON: That's the big picture. But medical researchers hope the chimp genome will also answer some highly specific questions. Francis Collins directs the National Human Genome Research Institute at the NIH. He says one of those questions has to do with cancer.

Mr. FRANCIS COLLINS (Director, National Human Genome Research Institute, NIH): Chimps don't get cancer at the same level that humans do. We don't know why that is. So being able to compare the genomes letter by letter to try to understand those differences and how we might capitalize on them to improve medicine was one of the main reasons to do this study.

HAMILTON: Collins says scientists have already found one genetic difference that could add to their understanding of Alzheimer's disease. The difference involves a gene called caspase-12. It's involved in the degeneration of brain cells. In humans, caspase-12 is turned off, but Collins says no one knew if that was unusual.

Mr. COLLINS: We've thought for some time, well, that might be something that's true of lots of organisms. It looks like it's just true of us because the chimpanzee has a functioning version of that gene, and chimps don't seem to get Alzheimer's, at least not as far as we know, at the level that we do. So maybe there's a connection there.

HAMILTON: The chimp genome also is helping scientists figure out how humans are changing. Lander says chimps and humans took different genetic paths about six million years ago.

Mr. LANDER: Darwin is still at work. Species are still evolving in response to environments as they change. Our environment is certainly not fixed in any way. It's been changed over the last tens of thousands of years by civilization and diet and infectious disease, as it's being changed today, for example, with the AIDS epidemic in Africa. And genomes still respond.

HAMILTON: So far scientists have identified several types of genes that are changing faster in both humans and chimps than in other animals. These include genes involved in perceiving sound and transmitting nerve signals. The research on the chimpanzee genome appears in the journals Nature and Science. Jon Hamilton, NPR News, Washington.

SIEGEL: You're listening to ALL THINGS CONSIDERED from NPR News.

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