Pondering the decline of Neanderthals

[Belushi TD]

Question - Is the biological definition if two individuals are of different species is if they can't breed with each other? If so, and assuming that the so called "Neandertal" genes in modern humans are due to interbreeding, wouldn't that mean that Cro Magnon and Neandertal were just VERY differently expressed variations of human, akin to how asian and african and european people all are visually very different looking?

Belushi TD

That is a very good question. Tell you what - give me $50 million, eight years to get a doctorate in anthropology and genomics, another 20 years to research the question, and I promise I'll get back to you with either the answer or a reason why I need another $50 million to narrow the research field further.

If I had 50 million to give, I'd be all over that. Since I don't, we'll have to see if we can convince Musk or Bezos to fund it!

Belushi TD

[David Newton]

One definition of a species (at least for animals) is a population that cannot interbreed with those outside the population and produce fertile offspring. Hence although things like mules, ligers and tigons exist, since they are infertile horses, donkeys, lions and tigers are correctly regarded as separate species.

However there are complications to that definition as it's not the only one. Another definition is populations that whilst they can interbreed if they meet are so geographically isolated that in practice they never meet. A second hiccough are ring species. In the UK there are herring gulls and lesser black-backed gulls. In the UK they are clearly separate species as they are in the same location and they cannot interbreed with each other and produce fertile offspring. Except … follow the populations opposite ways around the artic region and there is a continuum between the two that can interbreed with each other! Kind of the taxonomic version of the political horseshoe theory.

With plants it gets even more complicated as they are vastly more likely to hybridise than animals are and in some cases those hybrids can produce fertile offspring. A good example is Aesculus hippocastanum and Aesculus pavia. One the common horse chestnut from the Balkans and the second the red buckeye from the south and south eastern US. So in ordinary circumstances never likely to come into close contact with each other. However with human movement of specimens they have and the result is Aesculus × carnea, the red horse chestnut. The flowers of pavia, the morphology of hippocastanum and intermediate in size between the two. One set of the hybrid don't seem to be fertile, but more recent ones do appear to be fertile. So, like I said, it's complicated with plants.

Bacteria and archaea? They can just straight swap genetic material with each other directly!

So turning to Homo sapiens, I think it's wrong to call Neanderthals and Denisovans separate species from us. Clearly fertile hybrids could be produced when they came into contact with each other. All three combinations have been found. So the most accurate thing to call them and us are subspecies of Homo sapiens.

[Nathan45]

Yeah the species concept is one that is a lot fuzzier then we thought it was when we came up with it. For example, Polar bears are recently descended from Grizzly bears, and still occasionally hybridize with them, and (This is critical) those hybrids are fertile and can sometimes still mate with both respective groups, there is still some gene flow between them. (So not like a mule, which is sterile hybrid between horses and donkeys.) If you go by the old hard school definition of species, Polar bears are Grizzly bears, they just have gone on a paleo diet for 300000 years.

But I don't think anyone can argue they are the same species.

Edited to add, most gene flow between polar bears and brown bears is from Polar to Brown.

[Micael]

It is my understanding that Neandertals would have needed significantly more resources to survive than cro magnon man, as someone else stated earlier. Is there a climate changes back around the time of their extinction? Another question - Could there have been some kind of a virus or bacteria that Neandertal was susceptible to that Cro Magnon was not?

While the discussion about the domestication of the wolf is very interesting, and also the conversation about fighting between the two groups, we shouldn't let ourselves be blinded to other possibilities.

Question - Is the biological definition if two individuals are of different species is if they can't breed with each other? If so, and assuming that the so called "Neandertal" genes in modern humans are due to interbreeding, wouldn't that mean that Cro Magnon and Neandertal were just VERY differently expressed variations of human, akin to how asian and african and european people all are visually very different looking?

Belushi TD

Concerning the question of whether or not Neanderthals were of a different species than us, this is a matter that is still being debated. There was an earlier period in which we were considered the same species, then came a stint (maybe around the 1980’s to 2010’s) when most went for the separate species approach, but now the earlier stance has made a comeback. It’s worth noting that the more fervent proponents of the separate species stance often contained in within their arguments things in the vein of ”since we now know that Neanderthals and humans didn’t interbreed they must be considered separate species.” Then the archeogeneticists went and ruined that for them by showibg that we did interbreed, and a fair bit at that.

My current stance is that we have to be considered as two sub-species within one overall species. Not primarily due to modern humans and Neanderthals having the ability to interbreed but because they also did that. We as current day humans stem from both the ”modern human” lineage, and the ”Neanderthal” lineage. We are them and they are us, both of them. So either we have to consider ourselves a de facto hybrid species, or we take the approach that Neanderthals were the same species as their contemporary modern humans. The implications of the former approach would be that Neanderthals and their contemporary modern humans were of separate species, but that current day humans are the same species as Neanderthals, and of then modern humans. Alternatively that current day humans make up a new species altogether, only created at the point of admixture. But if so how do we deal with the complications stemming from the Denisovans? Only some current human populations seem to have admixture from them, are they then a separate species?

I believe that treating modern humans, Neanderthals, and Denisovans as sub-species within a species makes the most sense. All three were closely related and exhibited less physical and (as far as we can tell) behavioral variety than what you would find amongst for instance modern dogs, which are considered a single species.

A greater complication that may require far more consideration could come when we start to ponder the implications of recent genome studies that tentatively indicate admixture in some populations from more archaic humans than the aforementioned ones, such as likely either Homo Habilis or Homo Erectus, or both. If those results hold up over time it would mean that it was still possible for the more modern human varieties to breed with remnant population of so-called super-archaic humans. Per the originally stated definition of what a species is that would mean that us and Erectus/Habilis are one species, but of course the avenues for opposing that classification are many and wide given the greater differences in physiology and so on. But it is looking like an issue that we’ll have to adress.

[rtoldman]

I recall that last group of neanderthal bones were found in Spain. When I say last I mean that from dating the remains they appear to be the last surviving group. If the loss of megafauna is a theory then the last herd of prey would likely be in that area as well?

Is there any evidence to suggest gestation time for neanderthals was any different than modern humans?

[Sukhoiman]

think the gestation period of all our "on the same overall branch" ancestors would be similar to humans (homo sapien)

The chimpanzee (closest to us on a different enough branch) gestation period is apparently 243 days compared to human 280 days.

I remember reading/watching somewhere the Neanderthals were not only big game hunters but also adept fishermen and small game hunters....so I dont think their progressive extirpation ("as is" given concurrent merging into homo sapiens) is going to be 100% correlated to big game loss....they would have switched /migrated to other resource areas.

But of course this means coming into competition with the homo sapien settlers/migrants and resident neanderthals in those areas and so on. Population capacity in such format is limited till you develop farming and urban clusters so we can posit some conflict and "less prime area" push (and then sensitivities of smaller populations to further conflict, disease, malnutrition, genetic disorders from relative marooning... what have you)....so the ice age end did have some impact on neaderthal decline, we just dont really know how much compared to other factors.

[Nik_SpeakerToCats]

And, always, the head-scratcher of the Basque language, which appears to have endured from before the Indo-Europeans arrived...

Dare we ask if that area has been tested for an 'excess' of Neanderthal genes ??

[David Newton]

Wrong timeframe.

PIE (Proto Indo European) was around about 6 ka, whereas Neanderthals winked out 38 ka. So any language spoken around the time of Neanderthals leaving the stage will be so far gone as to be utterly lost to the ages.