Gene 'copies' may help separate man, monkey
Monday, October 9th 2000, 12:00 am
By: News On 6
By Sue Goetinck Ambrose / The Dallas Morning News
PHILADELPHIA â€“ The makers of the upcoming Planet of the Apes movie may want to consult a geneticist.
The latest gene research is giving scientists new ideas about how lowly primates can reach higher branches on the evolutionary tree.
People, for instance, are primates that evolved from creatures with much smaller brains and were probably not that bright. Researchers have wondered for decades what special genetic features account for humans' intellectual prowess, said Dr. Julie Korenberg, a geneticist at Cedars-Sinai Medical Center in Los Angeles.
To figure out what makes people special, "we generally ask what the differences are between us and our closest neighbors, the chimpanzees and the great apes," Dr. Korenberg said last week at a genetics meeting in Philadelphia.
People's closest animal relatives are chimpanzees. About 5 million years ago, researchers believe, a primitive species of primate split into two groups. One group evolved into today's chimps, the other into many humanlike species, of which only humans have survived. (After chimps, humans' next-closest relatives are gorillas.)
Being kissing cousins, evolutionarily speaking, people and chimps share many genetic features. But the features they don't share are the ones that may tell scientists what makes humans human.
At the annual meeting of the American Society of Human Genetics, Dr. Korenberg and geneticist Evan Eichler reported on human genetic features that many researchers ignore. Most scientists concentrate on genes (segments of DNA, the molecule that passes hereditary information from one generation to the next) that are one-of-a-kind, present only once. But Drs. Eichler and Korenberg are focusing on genes that have near-carbon copies scattered throughout a person's DNA. These copies, they believe, may hold the secret to humans' special abilities.
It turns out that many of the genes that are so numerous in people are near-loners in more primitive primates. For instance, Dr. Eichler and his colleagues have discovered a gene that is present only once in Old World monkeys, distant relatives of primates like chimps and people. In orangutans, a primate that evolved later than Old World monkeys, there are a handful of copies of the gene. But in the most recently evolved primates â€“ gorillas, chimps and humans â€“ there are many copies.
Having more than one copy of a gene may not sound like a big deal. If you have one gene â€“ which would supervise a particular task in the body â€“ wouldn't it be a waste to tote around dozens of other copies? But the key, Dr. Eichler reported at the meeting, is that each of the copies of the gene is slightly different. Although Dr. Eichler doesn't know what the gene does, the fact that it has many look-alikes is a clue that it may be significant.
Genes like these "are potentially important breeding grounds for evolution," Dr. Eichler said.
After all, some of the most important genes in animals have near carbon-copies. Four sets of similar genes ensure that mammals, for example, sprout arms, legs and ribs in the right places on their bodies. Much simpler organisms, like the fruit fly, have only one set of those genes. So having lots of look-alike genes seems to let evolution charge ahead.
And there are at least 80 distinct families of look-alike genes in humans, Dr. Korenberg reported at the meeting. Right now, she knows where in the vast genetic instruction book those 80 families reside. Some of those gene families will be bigger in people than in chimps, she said.
The next step, she said, is to take a closer look at the genes that are more numerous in humans than in chimps. Dr. Korenberg said she wants to see whether any of those genes are important for people's distinct brain structure.
"The brain," she said, "is what has gotten us where we are."