There’s a very cool paper in the latest issue of Science that pinpoints a particular chunk of DNA that may have played a role in the evolution of a human-like hand from the hands of our primate ancestors. Not Exactly Rocket Science has the details. For some reason, a number of articles on the paper are using the hook that this segment of DNA was once dissed as junk. “A patch of DNA once regarded as ‘junk’ may hold the key to upright walking and opposable thumbs,” according to Wired. These reports seem to be following the language from the original press release.
The “Wow! Junk DNA is not junk after all” news hook is a tempting one, but it needs to be resisted. At the very least, science writers need to recall some history.
Less than two percent of the human genome consists of protein-coding genes. The “junk DNA” the news reports are referring to is the other 98%. But in the late 1950s, researchers discovered that short segments of DNA near protein-coding genes in E. coli played important functions. Proteins could clamp onto those segments to shut a gene down or to ramp up the production of the corresponding protein. In other words, scientists already knew fifty years ago that some segments of DNA that did not encode proteins were useful. This was not obscure research: the scientists got the Nobel prize. No big secret there.
The new paper about hand evolution reports on the discovery of a special kind of DNA segment called an enhancer. An enhancer sits very far away from the gene it enhances. But if DNA is folded in on itself, the two come close together. Proteins that clamp down on the DNA can then increase the production of the gene’s protein.
So, are enhancers an amazing new kind of junk that’s not junk?
Nope. The first reports of enhancers came out in 1981, 27 years ago.
In other words, scientists have known for a long time that at least some parts of the genome that are not protein-coding genes served a function. The particular kind of DNA that was discovered to play a role in the development of hands has been familiar to biologists for nearly three decades. It comes as no surprise that there are more enhancers to be discovered in the human genome. They’re just hard to find, because they’re so short and so far from the genes they enhance.
Those who do not know their science history are doomed to repeat bad news hooks.
(For more on this history, see this post at Genomicron.)
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