Old News is Interesting News

We continue to comment on things related to paleontology.  This is not our field, and we've commented mainly on what we believe are premature if not insufficiently baked speculations about what evolved for what in our early history of a species, around 2 million years ago.  But there is a more recent (paleontologically) story that is of interest and is closer, at least, to what we at least know something about.

For decades there have been debates about whether or in what sense Neandertals, a kind of fossil relative of ours that existed from about 400,000 to about 40,000 years ago in Europe, and similar creatures elsewhere, co-existed with our immediate ancestors.  Neandertal-looking fossils disappeared 40,000 years ago, but more modern looking fossils seemed to have become common about that time.  The question has been whether these were different species, where and for how long they might have been cohabiting contemporaries in Europe, and whether there was any mating between them.

Not long ago a relatively complete set of Neandertal DNA sequence data was reported, that confirmed that overall Neandertals seemed to have a deeper but somewhat separate common ancestry relative to us modern humans.  But bits of the Neandertal sequence seemed too similar ours to be part of that picture.  That suggested that there was, in fact, some admixture.  In turn, that means that Neandertals and our 'modern' looking ancestors weren't separate species in the clear-cut classical sense.  But the evidence is not overwhelmingly strong and it's statistical in the sense that common ancestry times and degrees of relationship among DNA sequences have to be judged in relation to probabilistic models of deep population history.

How that apparent admixture happened is a matter of demography--population size, location, contact and mating patterns.  If there were doubts about the fact of contemporaneity of the two groups, then clearly they could not have mated, and the genetic evidence would need some re-thinking.

Now there are reports of a human-ancestral fossil from England that has been recently dated to about 40,000 years, the first or oldest known modern-looking fossil in that part of Europe.  This is touted in the media, as usual, because all stories are touted as greatly as the investigators and co-conspiring journals can manage.  Still, if it is a 'modern' ancestor--the fragmentary nature of the bits of tooth and bone make that still open to discussion, it is evidence of the potentially long (thousands of years) co-habitation of modern ancestors and doomed Neandertals in Europe.

If the evidence holds up, the evolutionary dynamic question is what extent and kinds of contact and interaction would be expected to have taken place, and whether this is consistent with the sequence data as we described above.

The story, like all such stories, gets a lot of press ink, but one thing is important to think about before we get too excited.  There are already substantial differences among modern humans from South American to Africa, peoples who have been separated for around 100,000 years.  But they are clearly not separate species.  When people from one location travel to another, as Europeans and Africans and Asians have come to North America for example, they naturally mate.  There is admixture--but not species admixture.  So, first of all, Neandertal-premodern mating would not be a shocking surprise.

Secondly, the definition of 'species' is well-known to be problematic.  We know rather clearly from the Neandertal sequence data already available, that the Neandertals were about as close to us, relative to our mutual relationship to common ancestry with our closest relatives the chimps, as we would expect from the fossil dates.  So, if Neandertal sequences were from 40,000 years ago, and Neandertals split 400,000 years from our own lineage, but we had about 8 million years of overall common ancestry, you'd expect that 400,000 years ago, when we and the Neandertals were one species, we were already 15/16ths identical to each other compared to chimps (because 400,000 is 1/16 of the way from 8,000,000 years ago to today.  We were all essentially 'human' by then.

Thus even by the most species-separating, melodramatizing advocate of 'admixture', the Neandertals and humans were essentially already the same species in terms of their overall DNA.  Whether or not we 'could', or just didn't, inter-mix.

Of course if Neandertal and our various ancestors never lived nearby, then of course no sort of direct 'admixture' between the two could have taken place.  So if the DNA suggests something like that did occur, and if the existing fossil dates, reinforced by the dating of the new British find (no tea was found at the site, by the way), at least the opportunity for mating was there.  Opportunity may be nine points in the law, and the DNA suggest at least some admixture.

Still, thinking about it, while it's very newsy, there is nothing particularly scientifically important about the question from a genetic point of view.  Yes, there could be traits found in Neandertals but not in our lineage.  Bigger brow-ridges may be an example.  But we vary among ourselves in important traits (like disease susceptibility), and clearly in many physical traits as our 'racial' variation shows.  This may have a lot to do with genetics, case by case, but it has very little to do with species or admixture.

For these reasons, despite the genocentric focus of all the news, the really interesting questions are not  genetic ones.  They are cultural ones.  What were the Neandertal and pre-modern populations like in size, behavior, environmental preferences, language, technologies, and so on?  What were their mating patterns?  When they saw each other, what kinds of relationships did the two groups have?  If there was intermating, were there recognized kinship affiliations among the adjacent villages of the two groups?  Did they share religious, body-decorating, food preparation and preference, and so on patterns?

It is these things, not genes, that could have been far more important in determining what happened.  It is true that genetic differences, even in something like body smell, could have inhibited mating.  But why do so many go so far out of their way to suggest things, than to try to find cultural explanations?

In part this is because genes mean grants, the news media eat it up, and they're the causes-du-jour of our time.  It is possible, certainly, that there were genetic barriers (even our favorite self-promoting criterion of intelligence). But then to suggest that and yet see some intermating evidence, leads to forced explanations (such as, essentially, rape of Neandertals by aggressive, superior, violent 'moderns').  That, too, is catchy and may attract media as well as professional attention.  But so far, it's not supported by any actual evidence beyond the imagination.

Again, right under our noses is the most fascinating question of all: how one human-like species completely displaced or replaced another.  The Neandertals disappeared, if they were indeed more than a 'racial' group at the time.  But before that, even more surprising if current views are close to correct, about 100,000 or fewer years ago, premoderns spread out of a spot somewhere near east Africa, and the long-established Homo erectus creatures disappeared.

It's difficult to imagine how these things happened, other than by accepting superficial, nearly evidence-free speculations.  But in any case, those questions seem more interesting, and are certainly more challenging, than always focusing on genes.

Neanderthals are Soxier than ever

With the mounting evidence that Neanderthals are just humans, it's easier than ever to compare them to the Red Sox.

With their large brows and their super-jock bods, we have generally held Neanderthals apart as a separate, brutish species. And under the immortal wicked assumption that brawn cannot also have brain, there is practically an industry built on lampooning some members of our own species in comparison.

Exhibit A. (So meta, really.)

Back in Damon's Sox days, the Red Sox even called themselves a "bunch of idiots." (Causing cavemen, who were not idiotic at all, to roll over in their museum drawers.)

But the more that Neanderthal genes are studied (and cross-your- fingers that these results really are based on ancient caveman DNA and not modern lab-rat dandruff),  the harder it is to separate them into a separate species.

That is, the more we know about their DNA, the more fossils that are found to bridge the gaps, and the more artifacts that are found to blur cultural differences, well the less sense it makes to consider Neanderthals as being any different from other Paleolithic humans as the Red Sox are from the rest of us.

And so this begs the question, if Neanderthals are just humans is it appropriate anymore to refer to Neanderthal-human sex as "interbreeding"?

If "the Neanderthals" were just like" the French" or "the Inuit" then describing their extra-population mating behavior as interbreeding would be something you'd probably only do while wearing a white pointy hat or holding your right arm out in front of you like a hemiplegic Frankenstein.

So we could keep calling Neanderthals Neanderthals...okay sure. But instead of thinking of them as a separate animal from neighboring humans, we could just think of them as a separate baseball team.

Neanderthals had their own look, their own strategies, their own traditions, but when they got together with other humans they understood them well enough to play the same games. They could hit a homer just fine, in both senses of the phrase.

This year's Red Sox couldn't have made a link to Neanderthals more complete. They just collapsed--shrouded in mystery with hardly anyone able to really explain why--while others with less muscle managed to go on.

Neanderthals are Soxier than ever. But even though the derogatory stereotype no longer holds, fans would probably flip that thought the other way around.

Further reading: 
http://www.theatlantic.com/entertainment/archive/2011/09/the-red-sox-werent-cursed-they-were-just-terrible/245717/

Kissing cousins

Well, the latest episode of Our European Cousins has aired. Svante Paabo, who if anything knows how to play each side of the street as long as there are cameras there, has announced now that 1-4% of the modern human genome is derived by admixture with Neanderthals. In the past, he was comparably insistent in headlining that Neandertals had not admixed and were a dead lineage.

The paper reported in the news (on the BBC website, e.g.) appears in Science's new issue. Make no mistake, it's a good and important piece of work, long promised and finally arrived. It is a sequence of roughly the entire Neandertal genome compared to five available whole-genome sequences from modern humans. Getting and assembling anything close to a whole genome sequence from fragmentary bits in fossils, contaminated with DNA from other things such as bacteria in the earth where the individual fell thousands of years ago, is no easy task and Paabo's group has been one of the global leaders. Studies of ancient DNA are important because they provide direct evidence of the past, so where DNA is preserved it will remain valuable to sequence and interpret it.

One thing to note, that seems like double-think, but is not relevant to the points we want to make here, is that this Neandertal whole genome sequence is not the whole genome sequence of a Neandertal. This sequence is a composite assembled from ancient DNA extracted from three different individual Neandertals' remains. But 'the' human genome sequence online at GenBank is also a composite. Some technical issues are affected by this, but they aren't relevant here.

Whatever the details of the assembly, or whether variation among Neandertals was observed, the issue here is the origin of modern human sequences: did any of it descend directly from Neandertals, or were they an entirely separate group (or species, even) that separated from the common human stock and had no subsequent inter-breeding. That is, we today would have no descent directly from the Neandertals. Or was there some inter-group hanky-panky?

The new paper suggests that there was, but there are two major problems with that. The 1-4% are in segments that seem to have a different ancestry from the rest of the Neandertal genome, less divergent from us. The rest diverges from us by about the amount you'd expect given our joint time of separation from our common ancestry with chimpanzees.

The first problem is one we harp on regularly, the playing to the media and exaggeration of the results. In this case, the exaggeration was the definitive way the admixture issue was made melodramatic and definitive. It suggests that interbreeding was something exotic or immoral, like a human mating with a chimp, rather than what at the time would have been considered routine mate choice among individuals from neighboring groups.

They would probably have coexisted together in times when nobody moved very far, and would have differed from each other far less than, say, Africans and Europeans do today, and between whom mating is thankfully no longer a big deal in our society. In fact, the evidence reported is that this interbreeding occurred after both groups were part of the Eurasian population after its expansion out of Africa. In that sense, the groups may have diverged somewhat, and come in contact again later, and became good neighbors for a while. Whatever happened way back then involves our ancestry which is certainly interesting and worth knowing. But when the evidence is tentative so should be the claims.

But there is a second and much more important problem. It is a subtle issue, that in essence is that whether or not any direct human genetic ancestry traces back through Neanderthals basically doesn't matter related to how 'different' we are from them. In round numbers, here's why:

A copy of your genome and a copy of a chimp's (our nearest living relative) differ by about 2 to 5% in terms of DNA sequence. Two copies of the human genome today differ by about 0.1 to 2% depending on the comparison one makes.

We've been separated from our common ancestor by 7-10 million years. Corresponding to that, the paper shows that the Neandertals differ from modern humans by about 7% which is about what you'd expect given that (regardless of admixture issues) the Neandertal split happened only after about 90-95% of the time had passed since we and chimps split.

By that time, basically everybody was human, and in turn that means that overall we are essentially as similar to Neandertals as we are to each other (crudely speaking, we're 95% closer to them than to chimps). And of course the vast majority of sequence differences generally, and hence in this case, will have little if any function. If humans are virtually identical to each other then we are virtually identical to Neanderthals whether there was any inter-mixing or not.

But consider how much functionally meaningful (as opposed to evolutionary clock-meaningful) variation there is in modern humans around the world. Within our single species, there's plenty of room for differences, and they can be important. They can protect you in very important ways from the environment (as skin pigmentation does in the tropics), they can protect you from disease (as immunological differences among us do), and there is a lot of variation in behavioral abilities of all sorts. As many diseases show, even just one single DNA change can be lethal.

The point is that whatever important functional differences or similarities there were between us and Neanderthals need have nothing to do with whether there was any admixture between their populations and populations of our other direct ancestors. Natural selection will purge bad variation, favor sterling advantages, and ignore most of the rest wherever it comes from.

If there is major functional difference between us and our burly cousins, it is to be found in the relevant genes, not in the score card (or dance card) of our sequence differences. And they could have existed in them then, but not us now, even if there was inter-breeding.

This means that Dr Paabo is right to treat this as a story for publicity. Its scientific impact is far less than its human interest value. To portray the inter-mixing question as an important one about human function is to misrepresent (or misunderstand?) how genes and evolution work. But to understand that takes more than a sound byte, and of course that means not many people will be interested.

At the same time, there's nothing wrong with trying to find out, especially from direct genetic data when it's available, what we can about our closest, if dearly departed, ancestors.