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If we don’t yet understand why selection made us different from other apes, can we at least find out who many and what sort of genes differentiate us? “Humanness” genes have become almost a Holy Grail of evolutionary biology, with many laboratories engaged in the search. The first attempt to find them was made in 1975 by Allan Wilson and Mary-Claire King at the University of California. Their results were surprising. Looking at protein sequences taken from humans anc chimps, they found that they different on average by only about 1 percent. (More recent work hasn’t changed this figure much: the difference has risen to about 1.5 percent) . . . .

Now that we’ve finally sequenced the genomes of both chimp and human, we can see directly that more than 80 percent of all the proteins shared by the two species differ in at least one amino acid. Since our genomes have about 25,000 protein-making genes, that translates to a difference in the sequence of more than 20,000 of them. That’s not a trivial divergence. Obviously, more than few genes distinguish us. And molecular evolutionists have recently found that humans and chimps differ not only in the sequence of genes, but also in the presence of genes. More than 6 percent of genes found in humans simply aren’t found in any form of chimpanzees. There are over fourteen hundred novel genes expressed in humans but not in chimps. We also differ from chimps in the number of copies of many genes that we do share. The salivary enzyme amlyse, the example, acts in the mouth to break down starch into digestible sugar. Chimps have not a single copy of the gene, while individual humans have between two and sixteen, with an average of six copies. This difference probably resulted from natural selection to help us digest our food, as the ancestral human dies was probably much richer in starch than that of fruit eating apes. ~ Page 210/211

4 years ago. Edited 4 years ago.

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22 months ago.

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