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Caveperson Chemistry: Rewriting Our Family Tree

July 11, 2014

 

Located in the mountains of southwestern Siberia, the Denisova Cave takes its name from a Russian hermit named Denis, rumored to have lived there in the 18th century. When some intriguing bones were discovered in this cavern, the moniker derived from his long-dead hermit would gain a new use: as a shorthand for a stunning discovery about the world of our early human ancestors.

 

In 2008, Russian researchers discovered the finger bone of a young humanoid female. It was the wrong shape to come from a Homo sapien, but when scientists sequenced the DNA, it didn't seem to belong to a Neanderthal, either. They had found what appears to be an entirely separate group of early hominids whose time on this planet briefly overlapped with ours. A genetic cousin to us, and a genetic sister to the Neanderthal. They had found the Denisovans.

 

Where early Homo sapiens and Neanderthals split into separate species some 440,000 years ago, Denisovans didn't branch off from the Neanderthals until considerably later, more like 300,000 years.

 

Of course, there is only so much you can learn about a species from a single finger bone, and even when archaeologists uncovered two teeth and a toe bone, this somehow failed to fill in the entire picture. Did the Denisovans have art and tools? Were they capable of symbolic thought and language? Thus far, that handful of bones is keeping mum.

 

Here is something we do know about the Denisovans: it looks like they interbred with us. For instance, tests show that between 4 to 6% of the modern Malanesian genome seems to have come from them.

 

If that much interbreeding could take place, it does seem to suggest the Denisovans were not just crude ape creatures. And if they were anything like the Neanderthal, we should be careful not to immediately dismiss them as mouthbreathing simpletons who spent their days dragging around primitive spears and grunting.

 

While it is important to remember that the study of anything dating this far back involves an awful lot of guessing, researchers are increasingly gathering evidence that Neanderthals might have been much more advanced than we thought.

 

First of all, the simple Neanderthal spear turns out to require a fair amount of engineering.

 

Neanderthals weren't just finding sharp rocks on the ground, they were crafting what's known as "Levallois flakes": symmetric stone blades with a sharp edge all the way around and an even thickness, for easy resharpening. Even to an experienced modern flint-napper (yes, there are still flint-napping enthusiasts out there), making one involves considerable effort. First, you have to chip the flint into a precisely shaped symmetric starting piece called a "core". After all that work, you then have exactly one chance—one perfectly aimed strike—to knock off a flake.

 

These flakes were tied to spear shafts with a thin strip of animal hide, which was secured in place by a black sticky substance. And here we run into another problem: analysis shows it wasn't just tree sap lying around waiting to be collected. It was birch pitch, which doesn't occur naturally and would have required a fairly involved, multi-step extraction process: heating the bark up to a carefully controlled temperature while keeping out the oxygen and preventing the bark from burning.

 

But Neanderthals weren't just doing early chemistry, it appears like they might have been playing dress-up as well. Recent discoveries at Neanderthal dig sites include wing bones of birds of prey with cut marks on them. These wings would have had no real value of food, which suggests someone was stripping off the feathers, for what seems like decorative purposes. Other finds include little seashells sporting traces of hematite or iron ore, a red pigment, and neatly pierced little holes.

 

Although it's dangerous to draw too many conclusions here, it's hard to imagine a practical utility for this, and easy to suggest a more symbolic use, like jewelry.

 

All of these complex behaviors add weight to the increasingly possible, if still controversial, theory that Neanderthal culture included some form of language. After all, how would you teach pitch-brewing or jewelry-making to your offspring through a simple series of grunts? And considering that some of us got as much as 4% of our genes from Neanderthal ancestors, the Neanderthal-human hybrids didn't just happen, they were born into a situation where the group was willing to raise them into adulthood, which suggests a degree of cooperation that would've required advanced communication.

 

If you suspect you're carrying around some Neanderthal in your blood, don't worry: although we don't know the function, if any, of most of the surviving Neanderthal DNA, at least some of it appears linked to immune system responses, including a guard against the Epstein-Barr virus.

 

And while those Denisovan bones aren't yielding many of their secrets, Denisovan DNA may be the reason Tibetans can adapt to low oxygen levels at such high altitudes. According to a recent article in Nature, presence of this extremely unusual and helpful EPAS1 gene in the Tibetan people "can only be convincingly explained by introgression of DNA from Denisovan or Denisovan-related individuals into humans."

 

So remember, there's nothing to be ashamed of. And the next time you're facing an illness or climbing a mountain—or trying to distill birch pitch without the use of any modern technology—it might be time to call on your inner caveperson.

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