We are told that modern humans are survivors and most other human “species” died out. From Sarah Sloat at Sapiens:
Roberts and Stewart contend that the fossil record, as it stands now, demonstrates that anatomically modern humans had expanded to higher-elevation niches than their hominin predecessors and contemporaries by 80,000 to 50,000 years ago. At least 45,000 years ago, Homo sapiens were colonizing a range of intensely challenging settings, including deserts, tropical rainforests, and Palearctic regions.
That’s not to say that other members of the genus, like Homo erectus and Homo floresiensis, didn’t migrate far beyond Africa. But these ancient hominins stayed within an environmental comfort zone comprising a mixture of woodland and grassland. So far, says Roberts, we’ve only found fossil evidence of Homo sapiens in other settings, although “in some cases, like deserts, it remains debated how arid they were when humans got there.”More.
Other researchers take exception to the claims that being adaptable explains human success. One points out that we don’t actually know that other “species” of humans did not colonize the same areas. We don’t have fossil evidence – but then new fossil evidence turns up all the time. Indeed, some readers may recall the 2012 bombshell when Neanderthal art was found, obliterating many certified lesser human theories. Also, success based on factors unrelated to adaptability to difficult climates may have led to the population growth that forced some modern human groups to make do with less pleasant environments. They may not have been more adaptable; just more numerous.
Note: It’s not clear to some of us just how many human “species” there even were; the whole concept of speciation is a huge mess at this point.
If you are interested in a range of theories about how human uniqueness occurs:
See also: Researcher asks, if ecology caused the human brain to grow so large, what about the role of language?
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