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Brief note on thumbs and junk DNA

I was going to write about this paper about a gene that evolved rapidly in humans since our lineage split from that leading to chimps. But Ed Yong at Not Exactly Rocket Science has already done a great post on it, including a picture showing its likely link to thumbs.

Comments on Ed's blog and a more complete treatment on Carl Zimmer's "The Loom" (both favorites of mine) point out the fallacy of some popular press coverage claiming this is the first evidence that "junk DNA" isn't junk after all. They both make the important point that we've known for decades that some DNA that doesn't code for protein is nonetheless very important.

On the other hand, lots of our DNA really does seem to be junk. Much of it is the product of "jumping genes" that copy themselves and insert themselves into existing DNA. These are common because they copy themselves, not because they do us any good (although, just by chance, they may occasionally be beneficial).

About 5% of DNA that doesn't code for protein is nonetheless "highly conserved", as if it were somehow beneficial and therefore maintained by natural selection. But a paper I reviewed earlier showed that much of this conserved noncoding DNA can be deleted without apparent ill effects. So if it's beneficial, it's not very beneficial. Or maybe it's beneficial only under special circumstances.

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