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The emergence of these extinct human species from the fossil record raises a nagging question: what happened to them all?

Across the animal kingdom, single-species genera are somewhat uncommon. Why is there only one species of the genus Homo?

A related question. The extinction of the last surviving non-Sapiens coincides more or less with the retreat of the last glaciation period and the emergence of human civilization (see the chart midway into the linked article). These events also seem to have happened about the same time as the extinction of certain large land mammals such as the saber-tooth tiger and woolly mammoth.

Are these extinctions, large land mammals and species of Homo, connected in some way with the retreat of glaciers and/or the emergence of human civilization?

These questions are asked (but not really answered) in the first part of the book Sapiens.

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A asked a friend that asked one of their professors who nominally studies such things. He said probably same thing that happened to all the other mega fauna when modern humans showed up somewhere.

It's not lost on me what happened to Native Americans in North America when Europeans showed up. Disease, competition for resources, social disruption and war drove entire tribal groups to extinction. And Native Americans are Homo-sapiens not some random archaic Hominid.

Not a geneticist, but there is considerable genetic distance between various human populations due to pretty significant temporal separation between the populations of Sub-Saharan Africa, Eurasia, the Americas, and Oceania.

https://jaymans.files.wordpress.com/2014/05/global-genetic-d...

There are also various degrees of admixture from other human species (Neanderthals, Denisovans, something similar to H. naledii) in different human populations which also contributes to our genetic diversity.

https://upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Ho...

Some argue that these factors and others would suggest classification of humans as multiple subspecies, if not separate species. It should also be noted that the well-known definition of a species as "organisms that can mate to produce fertile offspring" is not the standard for all geni and families.

Homo erectus had an amazing range, both spacial and temporal. It inhabited the whole of the Africa-Eurasia landmass, and did so for over a million years (from 1.8Mya to 800kya). It is no surprise we're finding evidence of island populations that managed to survive even later (such as Flores).

As for the later stages,:

Sapiens or proto-Sapiens interbred with Neanderthals even earlier than the widely accepted cca 40kya admixture date; somewhere between 430kya and 270kya Sapiens dna enters Neandertal genome. While most of it was eventually bred out, mtDNA remained and all later Neandertal populations carried Sapiens mtDNA, with their original mtDNA disappearing

The reason for noncongruent out of Africa migration dates is that at least two occurred; other than the generally accepted cca 70kya migration, there was an earlier one which was limited to coastal areas of Arab peninsula, Indian subcontinent and SE Asia until it reached the previously unpopulated area behind the Wallace line, where it resulted in PNG and Australian aboriginal populations.

The reason for coastal-only migration until PNG was that those areas were already inhabited by Neanderthals and Denisovans whom Sapiens was unable to outcompete.

Only after Toba eruption (75kya) do those populations become weakened enough for Sapiens to outcompete them and that's when we see first successful migration to Middle East.

Maybe they simply got merged into us? We all have neanderthal ancestry.

Isn't "merged" a nice way of saying that the men and children were likely murdered and the women taken for breeding? "Merged" conjures an image of living peacefully side by side and interbreeding for many generations.

Isn't this ultimately the origin of everything that we recognize as a modern ethnicity? We're all the products of amalgamations of conquered/extinguished tribes, states, empires, and cultures, most of which are lost to history forever.

> "Merged" conjures an image of living peacefully side by side and interbreeding for many generations.

That seems to be what happened with Neanderthals, at least at first.

Incidentally any violence may have been from the Neanderthals because almost all of the genetic data shows Neanderthal ancestry from Neanderthal males and homo sapiens females, and not the other way around.

Maybe the Neanderthal were more sensitive and alluring to Homo sapiens females, given their artistic side.

> "Merged" conjures an image of living peacefully side by side and interbreeding for many generations.

Even when this did happen[1], the record seems to show trickles of gene-flow from these populations entering a much larger stream of genes from a more recently out-of-Africa population.

[1] And in a big complex world, it certainly would have happened sometimes.

Women are people too, so that wouldn't be how such merging happens. Most likely homo sapiens greatly outnumbered the neanderthals, so any neanderthals (whether more or female) that mated with humans had their own DNA diluted and eventually absorbed into the homo sapien population.

All matings that resulted in Neandertal DNA in modern humans were by Neandertal male + Sapiens female.

All (non-african)

At this point, some Africans probably have some Neanderthal in them.

Subsaharan Africans have mated with for now unknown hominin cca 30kya.

As for your claim, you're mostly right. There was an incursion of non-African DNA into Subsaharan Africa around 3000kya, probably related to Bronze Age Collapse and migrations around it. Because of this, Africans can carry up to 25% Eurasian DNA, and part of that is Neandertal.

https://www.bbc.com/news/science-environment-34479905

*around 3kya, I meant.

If there was ever any other terrestrial intelligent species much different from us, we probably killed them all.

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