Another humanoid species walked the earth

[I'm on vacation, and this short post will appear while I'm away.]

One of the coolest scientific discoveries of the past few years was a small bone found in a remote region of Siberia.  The scientists who found it initially thought it was just an early human fossil, or else a Neanderthal fossil, but something about it looked a bit off.  It was just one small finger bone, not much to go on.

But DNA sequencing told a different tale.  The bone belonged to a female who was neither human nor Neanderthal, but something in between.  She and her kind appear to be closer to Neanderthals than to modern humans, but there is no doubt that she represents a new hominid species, one that died out only recently in evolutionary terms.  The evidence indicates that this previously unknown group, called the Denisovans after the cave in which the bone was found, actually interbred with humans.

The latest findings were published last fall in the journal Science, by a team led by Matthias Meyer and Svante Paabo.  With just one small, 75,000-year-old finger bone, they knew that extracting DNA would be a challenge.  Most of the DNA from ancient samples comes from bacteria and other creatures that have infiltrated the bone over the millenia.  But they were lucky in one respect: Siberia is cold, and has been for a very long time, which helps to preserve DNA.  Still they had to develop an entirely new method of extracting ancient DNA for this bone.

Meyer and colleagues extracted enough DNA to cover the entire genome of this ancient female.  They estimated that Denisovans and human diverged over 175,000 years ago.  They also discovered that modern Papuans contain vestiges of Denisovan DNA in their genomes, about 6%, suggesting that interbreeding occurred when humans were spreading across Asia.

Just this month, National Geographic's Jamie Shreeve published a feature article on the discovery, providing a fascinating look at how a single finger bone revealed a previously lost sister species.  (I highly recommend it, even for those who read the original Science article.) Now that we know what to look for, we might find more, and learn more, about these almost-humans from ancient Siberia.  And maybe we'll eventually figure out why they disappeared.

A final note: this discovery is yet another example of how evolution has shaped the history of life on this planet, but somehow I suspect the anti-evolution forces in the U.S. will find a way to deny it.