In the summer of 2008, Russian researchers dug up a sliver of human finger bone from an isolated Siberian cave. The team stored it away for later testing, assuming that the nondescript fragment came from one of the Neanderthals who left a welter of tools in the cave between 30,000 and 48,000 years ago. Nothing about the bone shard seemed extraordinary.
Its genetic material told another story. When German researchers extracted and sequenced DNA from the fossil, they found that it did not match that of Neanderthals — or of modern humans, which were also living nearby at the time. The genetic data, published online in Nature1, reveal that the bone may belong to a previously unrecognized, extinct human species that migrated out of Africa long before our known relatives.
Carl Zimmer has about the best explanation I’ve found (no surprise – his writing on science in general, and evolution in particular, is nothing short of brilliant). Here’s a good excerpt:
The scientists succeeded in fishing out human-like DNA from the pinky bone, and so far they’ve sequenced its mitochondrial DNA–that is, the DNA that is housed in mitochondria, sausage-shaped, fuel-producing structures in our cells. The majority of our DNA, which sits in the nucleus of cells, comes from both our mother and father. But mitochondrial DNA comes all from Mom. When the scientists compared the pinky DNA to DNA of humans and Neanderthals, they got something of a shock. If you line up the mitochondrial DNA from any given living human to any other living human, you might expect to find a few dozen points at which they are different. Compare human mtDNA to Neanderthal DNA, and you’ll find about 200 differences. But when the scientists compared the Denisova DNA to a group of human mitochondrial genomes, they found nearly 400 differences. In other words, their DNA was about twice as different from ours than Neanderthal DNA.
The implication, again from Zimmer:
The Denisova DNA split too recently from our own to have been carried by H. erectus, the first globe-trotting hominids. But paleoanthropologists have found a fair number of other hominid fossils in Europe and Asia that might belong to more recent waves out of Africa. (Here, for example, is a report on hominids in Europe 1.2 million years ago.) So perhaps there was at least one other wave aside from H. erectus, the expansion of Neanderthals, and the spread of modern humans. If that’s true, this new discovery also means that this wave produced a long lineage of hominids that survived long enough to live alongside humans. We coexisted with yet another species of hominid–along with Neanderthals, H. erectus, and those lovable hobbits, Homo floresiensis–for thousands of years. Our current solitude is a recent fluke.
So, out of five (or more??) species of hominids, only we’re still here. Luck, or violence, or absorption – whatever the reason, at one time there were other similarly intelligent species right here on this one planet. I’m amused in how this supports my vision at the end of Communion of Dreams in two ways [spoiler alert!]: the revelation of humankind’s deeper history/ability and the fact that there are many other advanced races among the stars.
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