Humans did it to Neanderthals. And did it with them as well.
That, in a nutshell, is the summer's news about our evolutionary cousin. Two species, both alike in dignity. And so the tragedy unfolds...
It turns out that yes, humans and neanderthals spent some happy romantic hours together.
An article published in the July issue of Molecular Biology and Evolution confirms that variant genetic material on the X chromosome, identified in human populations throughout most of the world, is present in the recently published Neanderthal genome.
Dominique Labuda, lead scientist of the team, is quoted as saying "This confirms recent findings suggesting that the two populations interbred."
The genetic sequence in question is not found in sub-Saharan Africa, which allowed the team to propose that human ancestors gained it after they left Africa, and encountered Neanderthals already present in Europe, Central Asia, and the Middle East.
But this was apparently a Romeo and Juliet kind of love affair: and in the war between the Capulets and the Montagues of human evolution, Neanderthals were cast as the losers-- all their chances at a future wiped out.
According to an article published July 29 in Science, our invading human ancestors entered Europe in numbers far greater than the Neanderthal population living there, and simply overwhelmed them.
Or, to paraphrase: the Montagues were ten times more numerous than the Capulets. (In case you lost track, in this tragedy, we are the Montagues wiping out Juliet Neanderthal Capulet's family.)
Much of the news coverage of this story is actually rather vague about how the researchers arrived at their estimates of population numbers-- for that, you need to read the original article.
There are no direct ways to count populations of Neanderthals and the modern humans who replaced them. Instead, the researchers used three indirect ways to measure the relative population sizes.
First, they identified sites from the different phases that archaeologists associate with the last purely Neanderthal occupations and the first settlements of modern humans in this area of Europe. The number of sites went from 37 to 147 after the new population arrived.
Site numbers alone could be misleading: think of comparing the population of 147 villages to the 37 largest cities in the US. You need a way to estimate the actual population living in these settlements.
So the researchers, Paul Mellars and Jennifer French of Cambridge University, did a second calculation, estimating how much meat each population consumed (using discarded animal bone) and how many stone tools they used. If you assume there was no reason for the new people to be going through tools faster, or consuming more meat per person, then you can use these to estimate relative population size.
Finally, they factored in the area of sites.
These three measures came up with projections that the new human invaders were present in roughly double to three times the numbers of the Neanderthals who preceded them. Because each measure is independent of the others, the authors multiplied them to get an estimate of around 9 times the population of newly arrived humans compared to their predecessors, the Neanderthals.
Put another way: there were more sites; bigger sites; and apparently, the new humans occupying them were there in larger numbers, based on the refuse they produced.
And so, the tragedy enters its inevitable downturn, as our Capulets find themselves besieged by Montagues in greater numbers and withdraw to try to maintain a viable population, ultimately failing...
There is something funny, though, about the way these new insights are expressed-- or at least, perceived by and represented in the press.
What bothers me about these scenarios isn't the science. That is exciting; to be here at a moment when the confluence of creative researchers, careful field work, and application of new laboratory techniques is yielding so much more information about Neanderthal life is amazing.
We suffer from assuming a kind of species-consciousness; when we look back, we see two groups-- humans and Neanderthals--and we assess the way one species pushed out the other, as if we were talking about modern nations setting out on deliberate campaigns of domination.
The evidence, though, suggests something different.
It appears some Neanderthal damsel alive more than 50,000 years ago dallied with a Homo sapiens Romeo. We know that because traces of her genes are still in our corporate human genome.
This isn't something remote from our experience: it is old-fashioned sex.
Labuda, commenting on his team's research, ends up sounding like he is describing an individual tryst:
"This one event which led to this on the human X chromosome has to occur very early after modern man left Africa."
This one event.
This date. This ball held by Neanderthal leaders, inflitrated by young men from the upstarts who just moved into the neighborhood, and were threatening to over-run it.
This is what bothers me: there is a mis-match between the level on which things happened-- the gradual infiltration of the neighborhood by new groups, recognizably similar enough that some sexual liaisons took place-- and the level at which they are interpreted.
Were Neanderthals and the first human groups that entered their territory aware of each other's differences and similarities in the kind of tribal fashion captured in Romeo and Juliet? Did they reflect on the actions taken by each individual and credit them to, or hold them against, a larger group?
The interactions that overwhelmed Neanderthals took place at a much finer grain than the one that dominates news reports. Not two species, but two villages.
Or even two families, "both alike in dignity":
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life;
Whose misadventured piteous overthrows
Do with their death bury their parents' strife.
One of the families ultimately couldn't survive the deaths they suffered, and disappeared, except in the traces left in their opponents' offspring.
And that makes this a tragedy we can comprehend, not just a distanced story of one species replacing another.