[language] Gene separates early humans from apes]

[H.M. Hubey]

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Gene separates early humans from apes
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http://www.swissinfo.org/sen/Swissinfo.html?siteSect=143&sid=1296455

August 26, 2002 10:15 PM
Gene separates early humans from apes

By Maggie Fox, Health and Science Correspondent


WASHINGTON (Reuters) - A gene that separates humans from the apes and all
other animals seems to have disappeared from humans up to three million
years ago, just before they first stood upright, researchers have said.

Most animals have the gene but people do not -- and it may be somehow
involved in the expansion of the brain, the international team of
researchers said on Monday.

The gene controls production of a sialic acid -- a kind of sugar -- called
Neu5Gc, the researchers write in an advance online issue of the Proceedings
of the National Academy of Sciences.

"This mutation occurred after our last common ancestor with bonobos (pygmy
chimpanzees) and chimpanzees, and before the origin of present-day humans,"
they wrote. Neanderthal skeletons, the oldest early humans from who DNA has
been obtained, also lack the sugar.

"It happens to be first known genetic difference between humans and
chimpanzees where there is a major outcome," Ajit Varki of the University of
California San Diego, who led the research, said in a telephone interview.
"We are exploring the consequences of this."

Varki said the role of the gene is not fully understood.

"The gene itself is involved in changing the surfaces of all cells in the
body," he said. "The surface of all cells in the body is covered with
sugars. This one is missing only in humans."

It may help influence how viruses and bacteria infect cells, and with how
cancer cells interact, Varki said. "There are some clues that it might have
something to do with brain plasticity," he added.

Humans and chimps share more than 98 percent of their DNA, so a few genes
must make a big difference. Chimps and humans split from a common ancestor 6
million to 7 million years ago.

The collaboration of some of the top experts in various fields, ranging from
anthropology to the genetic differences between people and apes, determined
that this gene disappeared from humans between 2.5 million and 3 million
years ago.

"It happened after the time that our ancestors stood upright, when their
hands and so on were like ours, but their brains are still same size as that
of chimpanzees," Varki said.

"That just tells you the timing is appropriate for the possibility that this
may have something to do with brain expansion."

The team included anthropologist Meave Leakey of the Leakey Foundation in
Nairobi, Kenya, an expert in early humans, and Svante Paabo of the Max
Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who
helped study the first Neanderthal DNA.

Reuters


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M. Hubey

hubeyh at mail.montclair.edu /\/\/\/\//\/\/\/\/\/\/http://www.csam.montclair.edu/~hubey



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