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Saturday, December 29, 2007

Human evolution: It all began in Pasta City, see ...

Human evolution is an interesting puzzle, one that fuels a lot of speculation. In this article by Ewen Callaway in Nature News (doi:10.1038/news070903-21), we learn "that spit might have helped human evolution by enabling our ancestors to harvest more energy from starch than their primate cousins." (September 9, 2007)

It seems that our human genome has many more copies of the gene that makes an enzyme (salivary amylase) that turns starch into digestible sugars. According to a recent study, in societies where people eat lots of starchy food, they have more copies of the gene. Apparently, chimpanzees have only two copies of the gene, but humans have, for example, an average of 5.4 (low starch eaters) to 6.7 (high starch eaters). This shows that we adapt to our food environment, whether its Pasta City or Sproutsville, but then we hear,
Dominy speculates that perhaps the change propelled our ancestors to new heights by fuelling the evolution of large brains more than two million years ago. Alternatively, the new copies may have coincided with the rise of agriculture 150,000 years ago, he says.

Now if we are not sure whether the change happened two million years ago or 150,000 years ago, we might want to be a bit more cautious about its significance for the human brain. In any event, one biologist commented that, starches aside, humans eat a lot more meat than primate apes do, and that one may just as well say eating meat spurred human evolution.

Actually, that would make a lot more sense too. Outwitting a deer (or even a fish) is a bit more trouble than outwitting a beetroot.

(Note: You'd have to pay to read the whole article at Nature.)


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