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Published: Monday, 10/4/2004

Humans, apes may not have that much in common

The idea that humans and chimpanzees are almost alike genetically as two peas in a pod may be headed for science's trash bin.

Scientists long have known that chimps are humanity's closest relative. Humans and chimps evolved together, and had a common ancestor until 6-7 million years ago. Then their paths diverged.

One animal built cathedrals, airplanes, computers, and space ships. The other was content with building nests in trees.

More recently, scientists discovered that the DNA in chimps and humans is about 98.8 per cent identical. It suggested that barely 1.2 per cent of their DNA keeps chimps from looking and acting human.

Scientists thought that only a handful of genes might differ in humans and chimps. It led to hopes for identifying genes that made humans human -- accounting for superior brainpower, the ability to use language and speak, and other traits.

There might even be genes for "human nature" that give animals foresight and noble traits like self-sacrifice.

In addition, those genes could solve medical secrets, like the reasons why apes are resistant to the AIDS virus and other diseases.

New research, however, is cautioning that the genetic gap between humans and chimps may be much wider than 1.2 per cent.

Teams of scientists from Europe and Asia have completed the first comparison of a human chromosome and its chimp counterpart.

Chromosomes are packets of genes located in the nucleus of cells throughout the body. Humans normally have 46 chromosomes, and they contain more than 30,000 genes that make up the human genome. Genes, of course, are stretches of the genetic material DNA.

Genes spell out instructions for manufacturing tens of thousands of proteins. These proteins are different than the familiar proteins found in food. Among them are proteins that change one embryo into a human and another into a chimp, make-up body structures, regulate how the brain and other organs work, and do everything that keeps people alive.

As expected, researchers found that human and chimp DNA is very similar, differing by only about 1.4 per cent.

However, the DNA that does differ contains 68,000 "insertions" and "deletions." Insertions are extra letters in DNA's instructions. Deletions are missing letters. Scientists can't always tell the difference, and so term these changes "indels," short for insertions or deletions.

Indels can mean dramatic differences in the proteins that genes produce. A gene with extra letters for instance, may make larger or smaller amounts of a protein or a dud protein that doesn't work at all.

It also may start or stop producing a protein earlier or later in an animal's development than a gene without extra letters.

The differences, scientists concluded, are enough to change about 83 per cent of the proteins produced by genes on this one chromosome. If that proves true for the other chromosomes, finding genes that make humans human and apes may be a lot more difficult than once believed.

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