I saw this article indicating that all modern humans have Neanderthal DNA: https://www.cnn.com/2020/01/30/africa/africa-neanderthal-dna-scn/index.html
Assuming for the sake of discussion that this is true, I was wondering about the taxonomy of Homo sapiens on iNaturalist:
Obviously, I’m not a scientist–I’m just curious about how that works when another member of the genus is also an ancestor.
No reason really to add hybrids, as we don’t call F500 a hybrid. I won’t call it an ancestor for 2% of genes, it’s a syster taxon that evolved from the same species (or group of close species emerged from heidelbergensis).
i suspect many (most?) species have some DNA from other related species like this, i know it’s true for many plants as well. So i’d say, probably not unless someone was somehow 30-50% neanderthal which no one is. But it shows how fluid ‘species’ are. This comes up with eastern coyotes a lot as they are part wolf and possibly part dog, but the average eastern coyote has way more wolf dna than the average human has neanderthal DNA
As I recall from anthropology classes years ago, neanderthalensis was once considered a subspecies of Homo sapiens rather than a separate species. Perhaps if enough evidence arises that early sapiens and neanderthals were interbreeding to a greater degree than what current evidence indicates, that taxonomic arrangement would gain favor again. But based on the currently-recognized amount of introgression detected, the past interbreeding of the two forms might not be enough to consider any revision of the taxonomy. As mentioned above, canids exhibit a lot more gene flow between species and although it makes species IDs tricky in some cases, it’s not likely to result in lumping of the various species of Canis. There’s a lot more gene flow across “good” species than what we used to think.
Then when a Homo sapiens and a Neanderthal had offspring tens of thousands of years ago, those might have had something closer to 50%-50% DNA, and been hybrids, but as time passes and further offspring are diluted there are no more hybrids?
Neandertalensis appeared from European heidelbergensis, sapiens from African heidelbergensis, so they’re completely different species that is proven by their DNA.
yes, those 50/50 individuals would have been hybrids…
There are at least two working definitions of species, and neither is clear cut. The contemporaneous criteria is that two groups can’t interbreed to produce fertile offspring. The retrospective criteria is that two groups didn’t. Really, both of these criteria are quantitative: my understanding of the current data is that humans and neanderthals could barely breed successfully, but managed nonetheless. And yes, these sorts of grey areas are super common.
My mental image of evolution is that it’s much more like a braided stream than like a family tree – lineages split and come together, and while we can group them into species, the finest-grained distinctions are neither deep or robust.
It really is such a messier situation than what we first learned in school, and introgressive hybridization is just one part of the problem. E.g., every Snowshoe Hare in Oregon, CA, and NV has Black-tailed Jackrabbit mtDNA.
so for those 50-50 individuals back then it would be accurate to say they had ancestors from both?
To complicate the picture even further, there is at least one other species/subspecies - the Densiovans - that is known to have interbred with both our lineage and the Neanderthals. Some groups of modern humans have even more Denisovan DNA than Neanderthal DNA, and may have interbred more recently.
So if I’m understanding right, at different points in time there would have been hybrids and ancestries appearing and disappearing, and that is the “braided stream”? This is all very interesting to me, because the taxonomy pages look so static and now I have a different visual in mind. (But I am a bit disappointed that after getting a report years ago stating that I have Neanderthal ancestry, I really don’t. That was the most interesting thing in the report.)
If you have European ancestry, you almost certainly have some DNA from Neanderthal–so, by definition, you would indeed have Neanderthal ancestry. There’s no specific percentage of DNA admixture that defines “hybrid”. An analogy is day fading into night–there is no specific moment when night begins (well, there is, but it’s artificially defined as when the sun is 18 degrees below the horizon). Introgression is the repeated backcrossing of an interspecific hybrid with one of its parent species. I don’t think most folks consider a third generation (or more) backcross to be a hybrid–but the cutoff is arbitrary.
Agreed. I suppose evolution could resemble a family tree if you assume a certain amount of incest was occurring (e.g., cousins marrying cousins).
The term semi-species is not used that often, but I suspect a lot of closely related taxa that we recognize as full species are in fact not fully differentiated lineages and are capable of interbreeding at least some of the time. Linnaean taxonomy simply doesn’t have the resolution to capture a lot of the “messiness” that goes on.
Well, the search you posted claims every population of sapiens have neanderthalensis DNA. If you’re not 100% African you have up to 2% of it anyway, it was known for years. If you’re from Oceania islands you also have denisovan genes, up to 5% as I remember, but the status of denisovan is now unclear, it’s called Asian heidelbergensis in the new family tree I see.
Denisovan DNA is not found in Western Asia, but a small component (about 0.2% on average) is found throughout Eastern Asia, and a much larger component (at least 5%) is found in throughout Oceania. By contrast, the component of Neanderthal DNA is about 1-2% in Western Asia. It’s been estimated that around 40% of the entire Neanderthal genome is distributed amongst modern humans.
These are introgessions, still hybrids.
https://scholar.google.it/scholar?hl=it&as_sdt=0%2C5&q=sapiens+neanderthal+introgression&btnG=
It’s still accurate to say that some modern Humans have both as ancestors. However not all modern humans have Neanderthals in their ancestry - those populations that remained in Africa did not have contact with Neanderthals. There are other Homo species, such as the Denisovans, that have also contributed genes to some (but not all) modern Human populations.
Not related to the hybridization within Homo, but the speciation of Panthera involved a lot of hybridization, however we still consider them their own species.
African Forest Elephants also have a good bit of Palaeoloxodon in them
A recent study may have overturned that idea (Chen et al. 2020, Identifying and Interpreting Apparent Neanderthal Ancestry in African Individuals). As always, some of the conclusions have been disputed, but it seems entirely plausible that some Neanderthals would have migrated back to Africa and interbred there. Or if not Neanderthals themselves, surely some Human/Neanderthal hybrids must have. The study found that about 0.3% of the genomes of African populations is Neanderthal.
