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100,000 years ago on earth there were several hominin groups, or bipedal human like species. 60,000 years ago homo sapiens began to move out of Africa and encountered these other species.

All of which evolved in Africa, all had left Africa at various times. For 10,000 years evidence suggests these groups lived along side each other. DNA evidence shows that all of these groups interbreed with the other groups.

They were:

My question:
Today only homo sapiens are left, why? Was the extinction of these other hominin groups due to direct competition, natural disaster, disease or what?

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    Nobody knows for sure, but there are some recently updated theories – sempaiscuba Mar 31 at 1:10
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    This is prehistory, not history. – Pieter Geerkens Mar 31 at 4:21
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    @PieterGeerkens - Human prehistory is on topic here. Hominid prehistory that's only a bit about Homo Sapiens is debatable though. (I'd be inclined to argue on but perhaps only because I happen to believe Homo Sapiens are probably a large part of the answer to this question.) – T.E.D. Mar 31 at 4:52
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    It appears to be in the nature of competition that one competitor wins. Premodern economics were negative sum games; if one species won, the others lost. We happen to live in a world where homo sapiens "won". Drawing any conclusion from this is like drawing a conclusion from the fact that the coin came up "heads" this time. We can establish the facts, but not the implications. – Mark C. Wallace Mar 31 at 15:42
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    In evolution, there isn't really a "won" or "lost", just changing in population levels. All of these species coexisted (or at least had their own ranges) for a hundred thousand years. Something appears to have happened to Homo Sapiens about 60,000 years ago that caused it's population to explode. Whether this was biological or cultural is an open question. Whatever it was, it let them outcompete the other species, either through direct violence, just being better at acquiring resources or through interbreeding as Pieter Geerkens suggests is an open question. Probably a combination. – Gort the Robot Mar 31 at 18:58
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You have answered your question here:

DNA evidence shows that all of these groups interbreed with the other groups.

Thus it is not that these other hominin groups became extinct - their DNA lives on in modern humans - but that most of their DNA heritage has evolved out of the modern line by virtue of being selected against.

Modern humans are the descendants of all of these lines. Over 90% of our DNA is identical to the other great apes. Another few percent is from the those other hominim groups that preceded Cro-Magnon man out of Africa. The remainder, a small percentage of our total DNA lineage, is uniquely inherited from the Cro-Magnon lineage.

We - modern man - are mongrels and hybrids who have benefited by possessing the DNA of all our ancestors.

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    This isn't settled science. Also bear in mind that you can in theory find lineage evidence in non-coding ("junk") DNA, and this wouldn't be selected out. Consumer tests that report "percent neanderthal" only check a limited set of genes, so it's impossible to relate with any confidence to levels of breeding. Part of the difficulty is that the concept of "species" is a human construct...the actual biology is much messier. – Gort the Robot Mar 31 at 18:55
  • @StevenBurnap: "Settled science" never exists; only "settled pseudo-science" does. – Pieter Geerkens Mar 31 at 19:56
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    Point taken. I just mean that the science around this is moving pretty quickly due to the dramatic improvements of the technology. – Gort the Robot Mar 31 at 22:24
  • Actually, non african homo sapiens have DNA of Neanderthals. Even though both are different branches of the hominim. – Santiago Apr 1 at 12:56
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    @Santiago: If you want to get technical: Just sub-Saharan Africans from west of the Great Rift Valley - because of back-breeding from Muslim conquest of the rest of Africa. – Pieter Geerkens Apr 1 at 13:01
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The book "Sapiens" by Yuval Noah Harari takes a look at multiple reasons. One can be genocide by Homo Sapiens, since they could compete for teritory and because they were different, genocides happened between Homo Sapiens too, so we are not the most tolerant race. Interbreeding is also possible, or a mix of extermination and interbreeding There might be the case that some humans in different areas of the world have more DNA from the other species, but scientis consider this theory Pandora's box since we know how people treat skin colour different, so you can imagine how lther species would be treated.

Disclaimer: That is my understanding of the stuff explained in the book.

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