The recent wave of inferences of archaic admixture in modern humans in a scenario that leans towards the "assimilation model" and/or "mostly out of Africa", "out of Africa with replacement and hybridization" (actual labels for models, even though often they're all lumped into "multiregional continuity") makes me wonder about the possibility of something similar having happened before Homo sapiens evolved.
There were quite a few African paleospecies, and just like sapiens and neanderthal, it's not possible to say with any certainty that they were 100% reproductively isolated during all their existence, so there's the possibility that similar episodes of inter-specific admixture were happening with Homo erectus/ergaster/rhodesiensis/heidelbergensis and before. And even between Australopithecines/kenyantropithecines, and those and earlier Homo.
Archaic admixture is not only detected by comparison with actual archaic sequences, but also pattern inference in genes of living persons, some alleles "look older." Can such methods somehow be used to speculate about the possibility of ancient admixture between earlier Homo? Could some of the inferred recent admixture with archaics be a more complex remnant of ancient admixture of this sort?
I also wonder how the different patterns of the degree of divergence between humans and the other hominids/anthropoids like chimps, gorillas and orangutans might be informative in one aspect or another. Wouldn't it be expected that at some point, humans also had a similar pattern of intraspecific divergence? And couldn't that create the illusion of "recent-archaic" admixture (mostly for statistically inferred admixture, not so much from comparisons) and/or preserve pre-erectus admixture?
I've read that chimps, gorillas and orangutans somewhat surprisingly more genetically divergent than humans, that's probably caused by smaller population size and less mobility. Even then, this doesn't cause any sort of dramatic "really evolutionary"/adaptive divergence, they're still much the same (I'm speaking more specifically about different chimpanzee populations separated by rivers, not taxonomically distinguished AFAIK, not the ones that are actually taxonomically distinguished, like chimpanzees and bonobos or the two/three types of orangutans and gorillas, even though even these don't seem to be significantly different, with the exception of bonobos perhaps). We also have trans-specific polymorphisms, that is, some people share alleles with orangutans, while others haven an chimpanzee allele, and others a gorilla allele. Also, as a whole these species diverge from each other in a mosaic pattern, not on an "homogenous" level. That is, we all have some DNA that's closer to chimpanzees, some that is closer to bonobos, some that is closer to gorillas, and even an entire chromosome that is closer to orangutans.
Can we also bring the "complex speciation" hypothesis into play, that notion that humans and chimpanzees first split 8-5 million years ago, but have hybridized without fusion around at about 1 million years ago, to only then split definitively? It was fist theorized by 2006 I guess, in order to explain the apparent antiquity of the X chromosome. The alternative explanation, which is favored I think, is that with a large enough population you could have the appearance of an X chromosome that could have come from such an episode of hybridization. Wouldn't that logic also apply for more recent inferred admixture?
I also wonder whether some entire species could be the product of the fusion of two other species. Like, first hominids split from gorillas, they remained isolated for a good while, and them some hominids (not sapiens yet, perhaps not even Homo yet, just the lineage) hybridized with a lineage of gorillas, producing chimpanzees. Or bonobos being hybrids of early-hominid (again, not even necessarily/probably Homo yet) and chimpanzees. Or heidelbergensis being an hybrid of Asian erectus and African ergaster (not that these possibilities "seem likely", they're almost random examples that just don't strike me as obviously impossible).
Do the researchers can take all that into account and make a coherent picture? I've only read news reports and abstracts or some parts of the actual research, I didn't have the impression that there's much concern with the possibility of complexity compounded by paleo-admixture/hybridization, at most they seem to take into account the possibility of modern population structure. But perhaps all this potential "complexity" I'm seeing is totally illusory, because of some explanation I simply don't know.
This is not a "make up your own fringe pet theory" topic, I'm just interesting in knowing whether some of these diverse possibilities are ruled out by mainstream, if they are. My way of viewing things isn't exactly contrarian/fringe, favoring some specific notion like one of these, despite of the lack of specific evidence or regardless of contrary evidence, but rather that things are complex and the only real certainty (in this subject) is something "broader", "Homo sapiens evolved from other hominids, seemingly arose first in Africa and essentially replaced earlier forms there and elsewhere, possibly with several degrees of hybridization". Encompassing the whole range of possibilities, with not much preference for hypotheses with more refined "resolution," but also not denying that they have different degrees of academic acceptance.
There were quite a few African paleospecies, and just like sapiens and neanderthal, it's not possible to say with any certainty that they were 100% reproductively isolated during all their existence, so there's the possibility that similar episodes of inter-specific admixture were happening with Homo erectus/ergaster/rhodesiensis/heidelbergensis and before. And even between Australopithecines/kenyantropithecines, and those and earlier Homo.
Archaic admixture is not only detected by comparison with actual archaic sequences, but also pattern inference in genes of living persons, some alleles "look older." Can such methods somehow be used to speculate about the possibility of ancient admixture between earlier Homo? Could some of the inferred recent admixture with archaics be a more complex remnant of ancient admixture of this sort?
I also wonder how the different patterns of the degree of divergence between humans and the other hominids/anthropoids like chimps, gorillas and orangutans might be informative in one aspect or another. Wouldn't it be expected that at some point, humans also had a similar pattern of intraspecific divergence? And couldn't that create the illusion of "recent-archaic" admixture (mostly for statistically inferred admixture, not so much from comparisons) and/or preserve pre-erectus admixture?
I've read that chimps, gorillas and orangutans somewhat surprisingly more genetically divergent than humans, that's probably caused by smaller population size and less mobility. Even then, this doesn't cause any sort of dramatic "really evolutionary"/adaptive divergence, they're still much the same (I'm speaking more specifically about different chimpanzee populations separated by rivers, not taxonomically distinguished AFAIK, not the ones that are actually taxonomically distinguished, like chimpanzees and bonobos or the two/three types of orangutans and gorillas, even though even these don't seem to be significantly different, with the exception of bonobos perhaps). We also have trans-specific polymorphisms, that is, some people share alleles with orangutans, while others haven an chimpanzee allele, and others a gorilla allele. Also, as a whole these species diverge from each other in a mosaic pattern, not on an "homogenous" level. That is, we all have some DNA that's closer to chimpanzees, some that is closer to bonobos, some that is closer to gorillas, and even an entire chromosome that is closer to orangutans.
Can we also bring the "complex speciation" hypothesis into play, that notion that humans and chimpanzees first split 8-5 million years ago, but have hybridized without fusion around at about 1 million years ago, to only then split definitively? It was fist theorized by 2006 I guess, in order to explain the apparent antiquity of the X chromosome. The alternative explanation, which is favored I think, is that with a large enough population you could have the appearance of an X chromosome that could have come from such an episode of hybridization. Wouldn't that logic also apply for more recent inferred admixture?
I also wonder whether some entire species could be the product of the fusion of two other species. Like, first hominids split from gorillas, they remained isolated for a good while, and them some hominids (not sapiens yet, perhaps not even Homo yet, just the lineage) hybridized with a lineage of gorillas, producing chimpanzees. Or bonobos being hybrids of early-hominid (again, not even necessarily/probably Homo yet) and chimpanzees. Or heidelbergensis being an hybrid of Asian erectus and African ergaster (not that these possibilities "seem likely", they're almost random examples that just don't strike me as obviously impossible).
Do the researchers can take all that into account and make a coherent picture? I've only read news reports and abstracts or some parts of the actual research, I didn't have the impression that there's much concern with the possibility of complexity compounded by paleo-admixture/hybridization, at most they seem to take into account the possibility of modern population structure. But perhaps all this potential "complexity" I'm seeing is totally illusory, because of some explanation I simply don't know.
This is not a "make up your own fringe pet theory" topic, I'm just interesting in knowing whether some of these diverse possibilities are ruled out by mainstream, if they are. My way of viewing things isn't exactly contrarian/fringe, favoring some specific notion like one of these, despite of the lack of specific evidence or regardless of contrary evidence, but rather that things are complex and the only real certainty (in this subject) is something "broader", "Homo sapiens evolved from other hominids, seemingly arose first in Africa and essentially replaced earlier forms there and elsewhere, possibly with several degrees of hybridization". Encompassing the whole range of possibilities, with not much preference for hypotheses with more refined "resolution," but also not denying that they have different degrees of academic acceptance.
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