Maybe we wiped Neanderthals out after all

Or at least, that’s the conclusion of a paper which models the population changes and other factors involved.

  • New model to study hominin interactions in time-varying climate environment.
  • Neanderthals experienced rapid population decline due to competitive exclusion.
  • Interbreeding only minor contributor to Neanderthal extinction.
  • Abrupt Climate Change not major cause for demise of Neanderthals.

Of course, a model is only as good as the assumptions that go into it.  But if it holds, Neanderthals went extinct due to competition from anatomically modern humans, as we migrated into Europe.  The alternate hypotheses, assimilation from interbreeding or climate change, turn out to be minor factors.

A series of maps showing that as Homo sapien populations increase, Neanderthal ones decrease
Homo sapiens and Neanderthal population changes from the paper. Source: https://www.sciencedirect.com/science/article/pii/S0277379120302936

I’ve never thought the idea that climate change was responsible made much sense.  The Neanderthals survived for hundreds of thousands of years through a wide variety of climate change events before we showed up.

The assimilation hypothesis in recent years seemed compelling, and there’s still reasons to think there was at least some assimilation, not the least that all non-Africans have 1-4% Neanderthal DNA.  But if the model is correct, it wasn’t the primary reason why they disappeared as a population.

Hank Campbell points out that it’s still possible we transmitted some disease(s) to them, similar to what happened when Europeans first arrived in the Americas and smallpox devastated native American populations.  But resource competition, again according to the model, seems more likely.

That said, I’ll be interested to see what public anthropologists such as John Hawks make of this.

First Peoples and Neanderthals

euros_cropped2

This weekend, I finished off the last of the ‘First Peoples‘ PBS miniseries on prehistoric humans.  If  you’ve watched other documentaries on human prehistory and found them interesting, then you’ll want to watch this one to get the latest findings.  It was fascinating.  (A lot of people have mentioned ‘Becoming Human‘ to me, which I’ve seen and enjoyed, but its content is now dated by a few years.)

I did find the sound editing in the first hour to be poor.  Often I couldn’t hear what the narrator was saying over the music or sound effects.  Hopefully they’ll fix that by the time the series is available in other venues.  If not, don’t let it deter you from watching the rest.  It gets much better after that first hour.  And the actual content of that first hour, on prehistoric native Americans, is fascinating if  you can bear with it.

In the final episode, we see anthropologist John Hawks discuss a theory about Neanderthals that I wrote about a few months ago, that they actually didn’t go extinct, but were assimilated into Home sapien societies.

A couple of decades ago, there were two major theories on the evolution of Homo sapiens.  One, called the Multiregional theory, posited that modern humans evolved throughout the world, with gene flow between the continents keeping humanity one species.  The other was the Replacement, or Out of Africa theory,  which held that modern humans evolved in Africa and then spread throughout the world, replacing other archaic human species such as the Neanderthals.

In recent years, the evidence seemed to swing decidedly in favor of the Replacement model.  All of the oldest remains of modern humans were found in Africa, and all archaeological signs of behavioral modernity throughout the rest of the world were less than 50,000 years old.  Genetic studies revealing the prehistoric migrations that Homo sapiens followed seemed to be the nail in the coffin of the Multiregional model.

All of which didn’t have modern humans looking too good in our relationship with other archaic humans.  It was starting to look uncomfortably like we had invaded their turf and drove them to extinction, either directly through conflict or indirectly through resource competition.

Then someone sequenced the DNA of Neanderthals and discovered that all ethnic non-Africans (from relatively recent times) share between 1% and 4% of their DNA with Neanderthals.  There was some discussion that maybe that shared DNA went back to the common ancestor of Homo sapiens and Neanderthals, but most scientists now see this shared genetics coming from intermixing.

In other words, Homo sapiens and Neanderthals mated.  If they did that, these two groups must have seen a lot more humanity in each other than had previously been supposed.  Neanderthals, since their discovery, have moved from an ape like conception to a branch of humanity that most of us have inherited from.

As Hawks discussed, Neanderthal population was probably never more than a few thousand individuals, while Homo sapiens migrating into their regions numbered in the tens of thousands, maybe even hundreds of thousands.  Neanderthals didn’t so much as go extinct as get swamped and assimilated.  Unless your ethnicity is African (again from recent historical times since we’re all Africans if we go far enough back), then you are part Neanderthal.

Depending on where your ancestors lived, you also may have bits of other archaic human population genetics in you, such as the Denisovans.

So, the verdict of evidence appears to be that the Replacement model was mostly right.  All of us are mostly descended from Africans, including the parts that make us modern humans.  But the Multiregional model was not completely wrong either since most of us have DNA from other branches of humanity.

Maybe we’ve found Neanderthals, and they are us.

The intermixing of modern humans and Neanderthals is back in the news: BBC News – DNA yields secrets of human pioneer.

DNA analysis of a 45,000-year-old human has helped scientists pinpoint when our ancestors interbred with Neanderthals.

The genome sequence from a thigh bone found in Siberia shows the first episode of mixing occurred between 50,000 and 60,000 years ago.

The male hunter is one of the earliest modern humans discovered in Eurasia.

The study in Nature journal also supports the finding that our species emerged from Africa some 60,000 years ago, before spreading around the world.

A year ago, I was pretty convinced that we, modern humans, were pretty much responsible for the extinction of the Neanderthals.  Various theories about climate change causing it didn’t seem compelling, since the Neanderthals had been around for hundreds of thousands of years, no doubt weathering many climate variations, but had disappeared right around the time modern humans encroached on their territory.

But the findings in recent years that all non-ethnic Africans have 2-4% Neanderthal DNA, has raised another interesting possibility.  (I wish I could find the article of the anthropologist who speculated about it, but I can’t, so you’ll have to read my amateur snippet.)

It appears that the population of Neanderthals was always low, a few tens of thousands across all of what is now Europe.  When modern humans started encroaching on them, those modern populations were orders of magnitude larger.  Maybe we didn’t eradicate Neanderthals or out compete them for resources (at least not completely).

Maybe we intermarried with and assimilated them.  It might be that Neanderthals didn’t so much go extinct as meld into the population of modern humans.  As someone who is 3% DNA (at least according to 23andMe), I find this idea intriguing.

Given the long history of us regarding the Neanderthals as some kind of ape-like sub-human, there may be resistance to this idea.  But the more I read and think about it, the more it seems like that’s where the evidence is pointing.

Maybe we’ve found Neanderthals and they are us.

When It Comes to Neanderthals, Humans May Be the Borg

The extinction and competition hypotheses for the demise of the Neanderthals, notably suggested by interdisciplinary scientist and author Jared Diamond, hinge on the idea that humans were more advanced than Neanderthals. Commonly claimed are the following: that humans had more communicative abilities, were more efficient hunters, had superior weaponry, ate a broader diet, and had more extensive social networks.

But the archaeological record doesn’t back any of those claims, the authors found.

In 2010, scientists discovered that between one and four percent of the DNA of modern humans living outside of Africa is derived from Neanderthals, providing clear evidence that the two species were interbreeding to some extent tens of thousands of years ago. In January of this year, Benjamin Vernot and Joshua Akey of the University of Washington published a paper in Science that corroborated those results. They found that a fifth of Neanderthals’ genetic code lives on within our species as a whole.

via RealClearScience – When It Comes to Neanderthals, Humans May Be the Borg.

As someone who discovered last year that they were 3% Neanderthal, and given the now very low population estimates for Neanderthals, this strikes me as completely plausible.  Maybe Neanderthals didn’t die out so much as marry into the family.  In other words, we are Neanderthals.  (At least those of us who aren’t from recent African stock are.)

Neanderthals were not inferior to modern humans, says CU-Boulder study

Neanderthals thrived in a large swath of Europe and Asia between about 350,000 and 40,000 years ago. They disappeared after our ancestors, a group referred to as “anatomically modern humans,” crossed into Europe from Africa.

In the past, some researchers have tried to explain the demise of the Neanderthals by suggesting that the newcomers were superior to Neanderthals in key ways, including their ability to hunt, communicate, innovate and adapt to different environments.

But in an extensive review of recent Neanderthal research, CU-Boulder researcher Paola Villa and co-author Wil Roebroeks, an archaeologist at Leiden University in the Netherlands, make the case that the available evidence does not support the opinion that Neanderthals were less advanced than anatomically modern humans.

via Neanderthals were not inferior to modern humans, says CU-Boulder study | University of Colorado Boulder.

There are still anthropologists who insist that the evidence for cognitive parity between Neanderthals and anatomically modern humans is scarce, but they seem to be increasingly drowned out by all those concluding that Neanderthals were very similar to us.  This article makes an excellent point that often Neanderthals are compared to humans living in much later times, and therefore more advanced times, in other words, comparing middle paleolithic Neanderthals to upper paleolithic humans.

It does seem increasingly evident that if Neanderthals were in front of us right now, that we’d regard them as people, not any kind of beast or semi-beast.  We may never know for sure though.

Neanderthals’ Genetic Legacy | HMS

“This suggests that when ancient humans met and mixed with Neanderthals, the two species were at the edge of biological incompatibility,” said Reich, who is also a senior associate member of the Broad Institute and an investigator at the Howard Hughes Medical Institute. Present-day human populations, which can be separated from one another by as much as 100,000 years (such as West Africans and Europeans), are fully compatible with no evidence of increased male infertility. In contrast, ancient human and Neanderthal populations apparently faced interbreeding challenges after 500,000 years of evolutionary separation.

“It is fascinating that these types of problems could arise over that short a time scale,” Reich said.

via Neanderthals’ Genetic Legacy | HMS.

An interesting article exploring the effects of Neanderthal DNA in the populations that have them (anyone whose heritage is outside of Africa).

I found the snippet above interesting.  I’ve seen a lot of discussion recently in paleoanthropology about whether or not the various prehistoric populations of humanity should be considered separate species, or just variants of the same species.  If us and Neanderthals were at the limit of compatibility, it seems to show that some of those other variants were probably not compatible.

My understanding of the definition of a species is that the individual members are genetically compatible enough for breeding.  If Neanderthals, separated by a few hundred thousand years, were only borderline compatible, it probably indicates that Homo Erectus was probably not, and probably should be considered a separate species, at least in my completely inexpert opinion.

Neanderthals and the Dead – NYTimes.com

Early in the 20th century, two brothers discovered a nearly complete Neanderthal skeleton in a pit inside a cave at La Chapelle-aux-Saints, in southwestern France. The discovery raised the possibility that these evolutionary relatives of ours intentionally buried their dead — at least 50,000 years ago, before the arrival of anatomically modern humans in Europe.

via Neanderthals and the Dead – NYTimes.com.

Similar to the changing understanding of the appearance of dinosaurs that I mentioned in my last post, is the changing understanding of the sophistication of Neanderthals.  Back in the 80s, Quest For Fire, one of my favorite movies, portrayed them as pretty brutish.  But information keeps coming in that they were more like us than previously thought.

This isn’t to say that they were exactly like us.  There were certainly differences.  But those differences don’t appear to be nearly as severe as we used to believe.  If we could talk with them today, we’d probably consider them to be human.  Certainly they were human enough to genetically intermix with our ancestors, at least to some degree.  (My 23andMe DNA results show that I’m 3% Neanderthal.)

I find the middle and upper paleolithic fascinating.  What kinds of lives did humans live in those times?  What were the relations between anatomically modern humans and Neanderthals?  We’ll probably never know beyond the glimmers we can get from archaeology and studying modern hunter gatherers.