Denisova: A Siberian Cave of Wonders

Corrie's younger cousin Richard, another guest at our Mexican wedding, is working on his Ph. D. in Biology. Before he moved on to that program, he was working with salamanders and was embroiled in the heated debate about "species". Generally different "species", when speaking of animals with obvious close similarities (nobody would argue about hippos vs giraffes vs lions), denotes different members of a specific genus which may have close--or not so close--physical similarities, but are unable to breed, or if they can produce an offspring, that it would be sterile. Think of a mule or a hinny. Richard studied enormous salamander colonies with hundreds of "species", entities normally recognized as different members of a genus, and sometimes even different genus, but they all interbred with each other, and all seemed to make viable offspring. A large writhing pile of humping salamanders, thirty-thousand deep. Spooky.

What does all this have to do with this cave in southern Siberia?



Many thousands of years ago, before that wooden stair system was installed, Denisova cave, as it's now known, was home to what are being called Denisovan hominids, a newly discovered line in the genus Homo.

It may be hard for us to understand, since today all we have is Homo sapian (I'm looking at you Sasquatch, a still hidden Homo habilus?), but at some point in the rather (geologically) recent past we had more than one specie of human. That's what it means to have more than one present member of Homo.

Depending on what evidence you believe is most accurate, eking out a life on this rock all at the same time were at least five different species of human: erectus, the oldest and most successful version (success defined in terms of years around); neandertalis, our close friends from those French caves who wrote songs and buried their dead; fiorenses, the pygmies from the Indonesian islands; our new Denisovan hominids; and ourselves, sapians.

Homo heidelbergensis might be the direct ancestor of both us and Neandertals.


Now, I've read many different discussions about the lineage of human beings, some with different branches with erectus coming out of Africa very early (for humans) and making it all the way to the far east and southern far east, another branch for neandertalis leaving Africa and settling in Europe, another branch slightly later for sapians, leaving Africa and heading everywhere. A different perspective suggested maybe that it's all one line, that we're all descended from Homo erectus...

In any case, the studies into the mitochondrial DNA of the Denisovan human show that they diverged from Neandertals around 350,000 years ago. They put the split between them and modern humans at over a million years ago.

Still, what does this have to do with salamanders? I'll let somebody else say it:

"Through genetic comparisons Pääbo’s team found that some people from Melanesia — an assemblage of islands off Australia’s east coast, including New Guinea — share 4 to 6 percent of their genomes with the Denisovans. This probably indicates that the Denisovans interbred with anatomically modern humans despite the split between our lineages over a million years ago."

And, in a different article, about a slightly different subject, in this guy Pääbo’s own words:

"Comparisons of the Neandertal genome to the genomes of five present-day humans from different parts of the world identify a number of genomic regions that may have been affected by positive selection in ancestral modern humans, including genes involved in metabolism and in cognitive and skeletal development. We show that Neandertals shared more genetic variants with present-day humans in Eurasia than with present-day humans in sub-Saharan Africa, suggesting that gene flow from Neandertals into the ancestors of non-Africans occurred before the divergence of Eurasian groups from each other."

You might find some of that incredibly interesting or incredibly boring, and then skipping it. The main point to take from both of those passages is that Neandertals and Denisovans interbred with modern humans, and have passed along genetic information.

So a specie is, uh...um...jury might still be out on that.

I have some pictures that may constitute evidence corroborating the claim of genetic material passed from Denisovans and Neandertals into modern humans.

Here is a guy from Papua, one of the the recipients of Denisovan genetic material:



Here is a guy who's ancestors came from Germany, among other places, a place that had it's share of Nenadertals, and even gave them their name (along with heidelbergensis). Check out his large brow and prominent nose:



One last picture that I wish was larger, a sort of family line-up of humans, members of the genus Homo: