Joseph Layden, Author of The Unnamed Bears Favor
There were lot more than that. We have at least five represented in our genome. There are a good deal more represented in the fossil record.
In short, the answer is “That’s how evolution works.”
Up until now, scientists have grossly underestimated the role hybridization plays in speciation.
For example, the ancestors of chimps and humans did not simply split apart 12 million years ago and then evolve into chimps and humans.
Rather, 12 million years ago one group of apes speciated into multiple types of ape. For the next 9 million years these multiple lineages occasionally interbred with one another. They formed many hybrids, which became species, which occasionally mated with one another….becoming more hybrid species.
Once, there were various species of apes all over Eurasia, Africa, and Sundaland.
The only great apes who survived multiple extinction events, assimilation/genocide by Denisovans, then assimilation by Neanderthals, then assimilation by us are Orangs, Chimps, Bili apes, Bonobos, and gorillas (and us).
Note: assimilation is the process by which one species “absorbs” another, keeping only the genes they need.
Before medicine, it was usually necessary for a species to gain immunities for a particular environment by hybridizing with sub-species who already lived there.
Until the Upper Paleolithic, there were usually at least two species of ape in any ecosystem; a large bodied and a small bodied one. Often there was a third medium-sized ape, either a hybrid of the two or an invasive species in the process of assimilating the other two. population moving in to assimilate both.
Thus, the various “ape niches” within any ecosystem were filled and exploited.
We are hybrids of various hominins that were assimilated during the Upper Paleolithic and Mesolithic.
We are one part tribe of Y Haplogroup Adam, one part tribe of Mito Eve, and one part tribe of LM3 (the “sister species” of Homo Sapiens who left a part of their mtDNA in our 11th Chromosome).
The vast majority of us are also one part Neanderthal. The few who aren’t live in very specific regions of Africa, and are one part something else: a hominid which split from us 1.3 million years ago, a hominid which split from us 700,000 years ago, or an archaic Homo Sapien population which split from us 325 thousand years ago represented by Y Haplogroup A00 (found in only a handful of people from Nigeria).
Some Polynesians and South Asians have genes from a species which broke off 3.1 million years ago.
Most Andaman Islanders and Pacific Islanders have genes from one or more species which broke off 550,000 years ago.
70% of people one Earth have a gene from the Microcephalin D hominid, which initially split from us 1.1 million years ago. And many humn populations have genes from various populations of archaic homo sapiens which split from us over 300 thousand years ago. For instance, most Siberians and Tibetans have genes from the now extinct Paleo=Siberians, and many Africans have genes from a group known as Paleo-East Africans.
This is not unique to ape evolution. Wild monkeys in S. America have introgressed genes from closely related “sister species” of monkey. Domesticated pigs are hybrids of at least three sub-species of wild pig.
3 views · Answer requested by Nir Levy
Why were there two different species of early hominids?
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