UPDATE: I can still see the viewable-by-all post of David Hillis; perhaps you have to be on Facebook yourself to read it. Here is the full text:
“Joao Zilhão, an archaeologist at the University of Lisbon, noted, with a trace of sarcasm, that the push to classify Neanderthals as a separate species frequently arises from a reluctance, especially among geneticists, to fully accept them as a geographically distinct, but interbreeding, branch of humanity.”
Exactly. Neanderthals were a geographically distinct population of Homo sapiens, rather than a distinct species. The two populations interbred extensively, and many modern people (including me) have both as ancestors.If pure Neanderthals were around today, no one would call them a different species, which would be considered highly insulting and racist. Why does the fact that we interbred them to extinction (actually intergradation) change that? Given that much of modern humanity carries Neanderthal genes in their genomes, it is time to stop making this misleading distinction.
Neanderthals are Homo sapiens, too.
For a long time I’ve maintained that Neanderthals, which most anthropologists seem to think are a species different from Homo sapiens, in fact constituted a population that was H. sapiens. That, at least, is a reasonable conclusion if you use the Biological Species Concept, which defines populations as members of the same species if, when they meet under natural conditions in nature, can interbreed and produce fertile offspring. And we know that’s true of Neanderthals and “modern” H. sapiens, because we carry some Neanderthal genes (I have some), and that means the two groups hybridized and that the hybrids backcrossed to our ancestors—and were fertile.
The bogus “species” is known to some as Homo neanderthalensis, which I reject. I have no objections, however, to Neanderthals being called a “subspecies,” or Homo sapiens neanderthalensis, as a subspecies is just a genetically differentiated population that lacks reproductive barriers from other populations.
The four or five “species” of giraffes that have recently been “recognized” are in fact just like Neanderthals and modern humans: bogus entities said to be “real species”; but in the case of the giraffes they don’t meet in nature so we can’t test their ability to interbreed in the wild. But they can do in zoos (and produce fertile offspring). There is likely only one species of giraffe. You cannot rationally separate species that live in different places by their DNA divergence alone. Those who love to divide up species for any reason whatsoever are known as “splitters.”
I’m glad to see that David Hillis, a widely-respected evolutionary systematist at UT Austin, agrees with me. Here’s his post on Facebook about the topic, prompted by an article in the NYT.
Yes, this has been a bug-a-boo for me for a while. I long ago stopped trying to explain why I think Neanderthals R Us. Even pointing out that we have some of their genes (I am, proudly, ~3.2% Neanderthal) has no impact. They are still thought of as different species. The media has done its job of confusing things so well that I don’t think it can be un-done. Eyes glaze over when I try to explain the BSC; I even used to pull “Speciation” off my bookshelf to help. Maybe it because I’m not a good teacher.
I wonder: What exactly does that 3.2% figure mean? Correct me if I’m wrong, but I am pretty sure that we share a large portion of our genetic material with all vertebrates, and of course an even larger proportion with all primates, not to mention close relatives like Neanderthals. So I would expect any modern human to be more than 99% Neanderthal, if you base it on a simple gene count. So presumably, the 3.2% must be on the basis of a much smaller subset of genes.
I am also a bit confused about exactly how a gene gets classified as “Neanderthal”. If it’s found in many modern humans, what is specifically Neanderthal about it?
Excellent question(s). I don’t actually know how they did it. My brother got it done; I know I’m his brother, so I just looked at his results.
But I know from my own background (genetics & immunoglogy) that regions of the human genomes have been discovered which are introgressed bits of DNA that match, in sequence and in distribution, the genome of sequenced Neanderthal DNA. I am assuming that the total amount of those sequences in my family amount to ~3.2% of my entire genome. But, like I said, I just read the report my bother sent me.
The way we tell how far away we are ancestrally from related species (getting to your question about sequence relatedness between us and our non-human ancestors), is complicated. But it’s done by the use of the same kind of sequence comparisons as noted above. When we find high degree of similarity between sequences, and we account for synonymous/non-synonymous and other changes in them, we can use a variety of statistical tools to construct phylogenetic “trees” (basically, pedigrees) which are best estimates for when we diverged from them.
The 3.2% refers only to sites in the genome that can be reliably identified in both species (called orthologous sites or genes) and that are variable sites (usually single nucleotide polymorphisms). In modern humans the number of variable sites across the whole species is ~600 million; “variable” usually means something like “the less common allele at the site has a frequency of at least 5% in the whole species” or “at least 1%”; everything else is a “rare variant”. Individual humans typically have ~4 million sites that differ from the human reference genome.
There are population genetic methods for deciding whether a shared allele is “Neanderthal” (arose in Neanderthals and was passed to humans by mating with them). The most convincing evidence is that these shared alleles are found ~only in modern humans in Europe and Asia, and are ~not found in modern humans in Africa. Neanderthals and modern humans split long before modern humans migrated to Eurasia, so most of those shared alleles can’t be shared ancestral polymorphisms that arose in Africa before the split (otherwise they would be found in Africans as well as Eurasians).
Interesting. I’d never thought of that before but of course the evidence of interbreeding automatically makes them part of a single species. Interesting also that zoos provide an opportunity to test the perspectives of lumpers v. splitters, and it sounds like the evidence is coming down in favour of lumping.
Well, it is not that good to use zoos. If two individuals from different populations produce sterile offspring in zoos, or mate but do not produce offspring, they would clearly also be reproductively isolated in nature. But some organisms that can produce fertile hybrids in zoos would not do so in nature, perhaps because they will mate under confinement only (I think there are some fertile mules, though not many).
I read in David Reich’s book ‘Who We Are and How We Got Here’ that there is rather complex genetic evidence that people who were hybrid H sapiens x H Neanderthals had very low fertility. I think that supports the claim they were a separate species
Comment by Greg Mayer
The best evidence for reduced fertility in Neanderthal-modern hybrids is the dearth of Neanderthal DNA on the X chromosome compared to the rest of the genome. This suggests that there was some problem with the reproduction of hybrids, as the X chromosome is often associated with post-zygotic reproductive isolating barriers.
I was firmly in the one-species camp, and still, on balance, would call them subspecies, but the X chromosome evidence suggests that the Neanderthal and modern lineages had progressed some considerable way down the path of reproductive incompatibility before they came back into secondary geographic contact and began exchanging genes again. (This is in contrast to the various geographic races of moderns, which have been separated a short time, and show no signs of reproductive incompatibility.)
It’s classic allopatric speciation– two geographically isolated moieties diverge in isolation to the point that they have some reproductive compatibility, but in this case they’ve gotten back together and merged back together, with one lineage (Neanderthals) contributing much less than the other.
I’m hoping that Jerry, one of the experts on Haldane’s Rule (the heterogametic sex is the sterile/inviable one) and the early stages of speciation will weigh in with his view of the paucity of Neanderthal DNA on X chromosomes.
John Hawks (who like me and Jerry, leans towards one species) has a discussion of the evidence, and Bret Payseur has a recent commentary on X chromosome effects in mouse hybrids. (Payseur seems to lean towards a one species approach, as well.)
GCM
I am dimly aware of that evidence, but that does not convince me that they are two species. They were clearly on the way to speciation, as are all isolated populations, but it got derailed. Because of Haldanes rule (sorry, apostrophe key broken at home), one would expect a paucity of X and Y-linked genes during introgression, as they are more likely to be involved in incompatibilities. This is, as far as I know, the first evidence for Haldanes rule in hominins.
I wonder if there is an archived version or screen cap of Hillis’ facebook post? It’s been made private and is not viewable 🙁
Wrt the NYT article a big flaw is that it repeatedly points to evidence for Neanderthal cultural or behavioural traits that occurred (in Europe and Asia) long before evidence for those traits in modern humans. The claim that Neanderthals did these things first is used to buttress the argument that Neanderthals were the equals of modern humans and coexisted with them for much longer than previously thought by those stupid and backward early evolutionary biologists.
The claim fails because there were no modern humans outside Africa at the times noted (>100,000 years ago), and conditions for preserving cultural and behavioural trace fossils are poor in most places in Africa where modern humans were living (and probably doing the same things Neanderthals were doing). It wasn’t necessary for the Times reporter to write with this bias, but I guess the bias lent a desired quality to the story telling.
When Hilliss post was put here, it was set to be viewable by everyone; otherwise I would not have posted it. At any rate, you can see his opinion from the screenshot.
Unfortunately I can’t see Hillis’s opinion. On my browser the screenshot says “This Facebook post is no longer available. It may have been removed or the privacy settings of the post may have changed.” Sorry for overcommenting.
As I say above, it has not been made private but was always public. I am a friend of Hillis on FB, but his post is supposed to be visible to everyone on the site (it has the globe symbol). I put the full text of his post at the top of the post above so you can read it all now.
I can only see a message saying it’s either been deleted or made private. Following the link gives me the same message.
I’m in Canada. That might be the reason? I think Mike Hart is in Canada, too.
I find these arguments about category somewhat pointless. For one thing, the relation of “same species” is not transitive. There are examples of species continua. Thus if A same species as B and B same species as C it does not follow that A is same species as C.
Linguists have the same issue with languages. Are Swedish and Norwegian distinct languages? Mutual comprehension is very high. Also both have considerable mutual comprehension with Danish. In past centuries before universal education and literacy produced standard languages, Scandinavia would have had a language continuum. Certainly the relation of “same language” is not transitive. Linguists are not at all consistent here. They usually call Swedish, Norwegian, and Danish distinct languages. But linguists usually classify dialects of Persian spoken by Tajiks and Hazara as the same language as standard Iranian Persian even though mutual intelligibility is less than between Scandinavian languages.
Years ago I read about a late 7th century document discovered in Andalusia. Naturally linguists wasted lots of energy on the semantic debate of whether that unique dialect should be called very late Latin or very early Spanish. Who cares which you call it! That dialect is its own unique thing. By definition, intermediate forms are intermediate and hard to pigeonhole into preestablished categories.
I think evolutionary biologists also sometimes waste too much effort to fit phenomena into preestablished categories. Does it really matter if we call a given fossil late Homo habilis or early Homo erectus? The transition was GRADUAL. If I plant an acorn and watch it sprout and grow, it would be silly to watch the plant with a stopwatch and try to pinpoint the second I should call it a “tree” rather than a “sapling”.
By the way, if one does want to quibble about the categories “Homo sapiens” and “Neanderthal”, where do the Denisovans fit in? As I understand it, they were reproductively capable with both sapiens and Neanderthals.
The bit about where it ‘does not follow that A is same species as C’ reads as parapatric speciation, where a candidate species is distributed over a wide geographic range, so that population A is far apart from population C — so much so that they do not have gene flow between them. It’s an interesting hypothesis for separation of species, but I don’t know of a real example where it works.
If we think in terms of geological time rather than geographic separation, it has to be true that same species” is not a transitive relation. Surely offspring are the same species as their parents. Yet we are descended from Homo erectus. Ergo we and erectus are the same species if same species is transitive. The alternative would be to say that a Homo erectus mom gave birth to a Homo sapiens kid. Surely that is silly.
We are talking about transitivity of existing populations here, not ones separated by large gaps of time
Sorry, but do not care if you think these discussions are pointless. They interest me and a lot of people, and there is no need for you to be uncivil like that. Nor do you give any example of intransitivity, and I do not know of any (there may be some, but none that I know).
And yes, it matters if a fossil is morphologically similar to a species that has been given a name, though morphology is not the optimal way to judge bilogical species.
So do not tell me that I and others are wasting our time. There are practical consequences, for example, for conservation if something is regarded as conspecific or heterspecific.
I certainly did not intend to be uncivil.
There are a couple examples of so called ring species that seem to be nontransitive if we take ability to produce fertile offspring as the criterion for same species. I think Dawkins somewhere discussed the example of Ensatina salamanders that live in a ring around the Central Valley of California. According to Wikipedia, the northernmost variant (Ensatina xanthoptica) and southernmost variant (Ensatina eushscholtzii) cannot produce fertile offspring though breeding occurs on a continuum.
Another example are so called greenish warblers of the genus Phylloscopus in Asia. The Tibetan plateau serves as a barrier, but the birds live in a ring around the plateau and there is a breeding continuum though distant species along the continuum cannot breed.
Google says that there is debate among entomologists as to whether Anopheles mosquitoes similarly form a continuum between distinct species.
And what about canids? Coyotes can breed with wolves or dogs. The offspring have somewhat reduced fertility, but they are not infertile. Perhaps early Homo sapiens and Neanderthals were almost as distant as coyotes and Canis lupus. Coyotes and wolves are usually regarded as distinct species.
Sorry, but you do not know what you are talking about. I discuss the Ensatina example in my book. There was not a geographic or breeding continuum as you assert; that is based on earlier and refuted studies. Same with the greenish warblers, studied by my colleague Trevor Price, who is next door to me. There is not a continual ring; like the salamanders, there are or have been extensive periods of allopatry.
I do not know what point you are trying to make, but you need to read about these examples in the up to date literature before you go saying stuff that is incorrect. And; that is the end of this discussion. I am tired of it, just as you said you are tired of people discussing the species question.
Maybe our successor species will name itself Homo sapiens sapientior, and/or rename us Homo sapiens myops.
The giraffe comparison is unforgettable – very … heuristic!
Neandertals share a lot of the same things as the people who followed them, like right handedness, dietary items, bone and stone tools, jewelry (eagle talons), intentional burials, cave art, and dark cave occupations (Bruniquel in France). As time goes by more and more similarities will emerge. 50 years ago, who would have imagined these discoveries, let alone the DNA. It is time to call them one of us.
If one thinks about speciation as a branching process where branching entails the evolution of reproductive isolating mechanisms, then modern humans and Neanderthals were one and the same species. Isolating mechanisms between populations either were non-existent or were insufficient to prevent gene flow. This would make modern humans and Neanderthals conspecific by definition.
The only caveat might be if the two were closely related species that exhibited some degree of hybridization. Can that be ruled out?
My colleagues and I often have this problem when trying to decide whether a newly discovered population of orchids deserves to be classified as a new species. With orchids, the fertility of hybrids in “captivity” is not a good enough criterion. Orchids even freely make fertile inter-generic hybrids when artificially grown in cultivation. Reproductive isolation in orchids depends on pollinator specificity, which can easily be screwed up by moving a plant to a very different habitat (like a different country) that has different pollinators.
So I have developed a rule of thumb for making these decisions. (I have mentioned this before in past comments on this theme.) If we know something about the history of the climate in the area of interest, we can sometimes show that the ranges of two distinct present-day populations would have overlapped during a cooler, or drier, or wetter climate than today’s. If the genetic divergence of the two populations is much older than that climate change, it is evidence that the two populations did not freely interbreed when they lived together, making them good biological species. And if the genetic divergence dates from around the age of the climate change that united the populations, then they are not good biological species.
Of course, as others have mentioned in these comments, evolution is a continuum and there will always be gray areas. But I find this criterion helpful. It would be interesting to apply this to the giraffes. We probably can estimate the geological ages of the deserts or forests that currently separate the populations. How does that compare to the genetic divergence times between these populations? I think this could help resolve this controversy. Maybe someone has done that?
I always found the details in this discovery about neanderthals to be one of the most remarkable stories about biotechnology, coupled with damn clever reasoning.
Finding terribly degraded DNA in fossil bones, and daring to get the seemingly impossible draft genomes out of that mess by pcr amplification, shot-gun sequencing, and then subtraction of identified contaminating DNA. This yielded a partial neanderthal genome. That was amazing. Of course they shared a lot of DNA sequences with our species, as would be expected for a close relatives. But then came the finding that these included shared genetic markers that were specific to Europeans and not other human populations. That singles out the conclusion that European H. sapiens were mating with neanderthals because they were encountering them. So the two are the same species. Damn brilliant bit of sleuthing, that is!
Honest question here, but what is the value of the category “subspecies”? I’m not a biologist (it was my worst subject in high school) but my understanding of “species” is that it is defined by the ability of its members to interbreed and produce fertile offspring. Is there some other condition that defines a set of members of a subspecies?
A subspecies is a population that is distinctive morphologically and has some genetic markers identifying it found in one geographic area. It has been partially isolated from the rest of the species, but still enough gene flow or not enough time has elapsed, to allow it to fully speciate. An example, is the Kodiak Bear (Ursus arctos middendorffi), a subspecies of Brown Bear that is only found on Kodiak Island, AK. They are typically larger (actually remarkably large for that species) than the mainland grizzlies (another type of brown bear). However, they are fully capable of breeding with other brown bears.
“Those who love to divide up species for any reason whatsoever are known as “splitters.””
Also known as The People’s Front of Judea.
Surely you mean The Judean People’s Front.
An additional complication would be at what point did Neanderthals become “extinct”. I assume there would be two possibilities, either they interbred so much with sapiens that any unique characteristics were erased, or they became isolated and their populations diminished to non-viability, as presumably other homo species did.
I think this is all very interesting. The question of how Neanderthals are related to Homo sapiens, and how we find ourselves with some Neanderthal DNA, is fascinating to me.
The idea that Neanderthals are a subspecies is new to me. With the morphological differences it seems complicated.