I was under the impression that was our doing. All of these human varieties were outcompeted by homo sapiens who replaced them. Modern humans don't need to worry about another hominid taking their place because we're the last one standing.
E.g. For at least 200k years, we can tell by fossils from the middle east that we made many attempts to spread to Europe, but were always pushed back. Fun fact: Neanderthals actually had substantially bigger brains that we do today (their average size was about 1400-1500ccs. Subtract the volume of a tennis ball from that and you'll get the average size of our brains today). Neanderthals were smart, tough, mofos.
So what changed 50k years ago which finally let us succeed? Well, the climate was warming from the last ice age, and Neanderthals were very much cold-adapted hominids. Their short, stocky legs and heavy muscular arms were great at sneaking through the woods and stabbing a deer with a spear, but when the climate changed the woods disappeared, those short legs, hauling a very heavy upper-body musculature, were not so good at running the deer down on a plain.
Honestly, we have no real definitive answer to why we are here and they aren't. Like anything else, probably it was a complicated process in which lots of factors--including dumb luck--played a role.
For about 4 million years, the earth was very hospitable to all kinds of species of Homo--we find their bones, in a kaleidoscope of shapes and sizes, all over the old world. Since the last ice age, however, Homo has been having a really rough time of it. And we are the only humans left.
If you were locked in a room with 10 people, and one by one they started to disappear, when you were the only one left, you might wonder whether it would happen to you too.....
FWIW this study suggests that Neanderthals and modern humans might have had very different approaches to language: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4766443/ Neanderthals and modern humans both evolved to make sophisticated vocalizations, but it's possible that the Neanderthals had 10000 words yet only a few ways to join them in simple sentences. (E.g. what if Neanderthals couldn't ask questions, only state disagreements?) In particular we know that humans can have local brain damage leading to near-total disability in using language while still being able to comprehend language, so you could see ancient hominids being "as smart as modern humans" in terms of general problem-solving - building tools, administering medicines and performing surgeries, long-term planning around food - but having profound blocks in language that prevented them from forming larger societies. Neanderthals tended to live in small family groups, whereas almost every modern human hunter-gatherer lives in a much larger tribe (absent war or disaster).
But IMHO it applies just as well when trying to show that Neanderthal’s language was super different from ours. We know virtually nothing about the evolution of language in our own species, let alone another species.
They were different for sure, but the fact that we regularly mated with and formed families with Neanderthals and their first few generation generations means to me that the difference wasn’t that much. I’d go so far as to that absent any reason to believe otherwise, the default presumption should be that we’d be close to equals with them in these matters.
To be clear there's only genetic evidence of admixture, not any evidence that humans and Neanderthals actually coexisted as families. Mating between humans and Neanderthals definitely wasn't "regular" since there's not actually very much neanderthal DNA in modern humans. Maybe we had an enormous number of infertile children, but I don't think human hunter-gatherers would survive that since rearing and raising a child is so costly.
In particular there's very good reason to suspect that we didn't form families with Neanderthals in the way you are suggesting[1]:
> No evidence of Neanderthal mitochondrial DNA has been found in modern humans. This suggests that successful Neanderthal admixture happened in pairings with Neanderthal males and modern human females. Possible hypotheses are that Neanderthal mitochondrial DNA had detrimental mutations that led to the extinction of carriers, that the hybrid offspring of Neanderthal mothers were raised in Neanderthal groups and became extinct with them, or that female Neanderthals and male Sapiens did not produce fertile offspring. [...] As shown in an interbreeding model produced by Neves and Serva (2012), the Neanderthal admixture in modern humans may have been caused by a very low rate of interbreeding between modern humans and Neanderthals, with the exchange of one pair of individuals between the two populations in about every 77 generations.
Even if it was 1 pair in 5 generations, that's simply not high enough to suggest a strong common humanity based on admixture alone. Pulling this all together, I don't think there's any real evidence that humans and Neanderthals co-parented or had any other real integration between their societies. There was just occasional admixture.
I am sure there's a paper somewhere but I've never read anyone actually rule out what is IMO the simplest explanation: Neanderthal men occasionally raped modern human women and the child was raised among modern humans (the reverse situation explains why children with Neanderthal mothers and modern human fathers would have been raised among Neanderthals).
[1] https://en.wikipedia.org/wiki/Interbreeding_between_archaic_...
There is not much evidence, but it's going too far to say there's no evidence. The evidence is their genetic heritage in us. There are many ways that that genetic heritage could have got there, ranging from rape to adoption to romeo-and-juliet style romances. The genetic admixture is evidence for all these routes.
// IMHO the simplest explanation: Neanderthal men occasionally raped modern human women //
That's one way it could happen, but we don't have anywheres near enough evidence to conclude that was the only way it happened, or even that it was the most common way it happened. All other hypothesis are still on the table.
And, certainly the first generation hybrids were welcomed in human families. Don't forget, in the Pleistocene, there was no such thing as being alive without being a member of a family.
This also led to the notion of a shared culture across many individuals that can adapt much more quickly than genetic evolution.
(Unless I misunderstand, of course.)
The author squarely blames Homo Sapiens for wiping out the other hominins, pointing out how many other large species seemed to go extinct as soon as we arrived someplace new, even long before the Agricultural revolution.
50,000 years ago, something changed . Maybe it was an increased capacity for abstract thought, but if so, that was a software and not a hardware development, because we had the same anatomy for 300,000 years. If we could implement the software, I don’t see why the Neanderthals couldn’t have done so, as they had even bigger brains than we do.
So maybe the abstract thought hardware was there for a long time before we got culturally coordinated enough to use it with full effectiveness to organize large groups capable of outcompeting Neanderthals.