The Case that Neanderthals were not Human - Genetics

The evidence suggests that Neanderthals were not human. There are several categories of evidence for this, but I’d like to focus on the very strong genetic evidence which points to this conclusion after just one point from morphology.

Of course humans have been changing somewhat for a while. Our modern globular brain shape did not even work its way into our phenotype until after 36,000 years ago, a date which some would say was near or after the date Neanderthals went extinct. I am not even convinced that the physical brain is what truly makes us human. But to the extent that it is brain shape may be even more important than brain size. Hominid brain size did not change much in almost half a million years while what humanity has accomplished from the time modern brain shape occurred to the present is orders of magnitude greater than those of other hominid groups given that same amount of time with a similar brain capacity.

Scientists tell us that all living Eurasians have an average of 1.5% of their genes from Neanderthals due to admixture events which occurred approximately 55,000 years ago. My own genome confirmed that this is the percentage in me. There is a caveat to this which I would like to address in a bit, but let’s go with that number for now. The discovery of a 40,000 year old Romanian male with somewhat more recent Neanderthal introgression seems to represent a genetic dead end who left no living descendants (else we’d find people with longer such gene segments than we do).

Indeed a comprehensive study showed that the lack of Neanderthal mtDNA (inherited from mothers) in modern Europeans despite thousands of years of the two living side by side indicated possible sterility problems between human males and neanderthal females and that the maximum possible number of such hybridization events over 12,000 years was 120.

Other studies indicate fertility issues going the other way. The human Y-chromosome is lacking in the “Neaderthal” genes present in the rest of the genome. The researchers concluded that modern human females and neanderthal males were not fully compatible. The most parsimonious explanation was that such unions could not produced fertile male offspring.

Put the two studies together and the lack of Neanderthal genes in both mtDNA and Y-chromosome DNA is consistent with the idea that the only pairing that really “worked” was a male neanderthal mating with a human female and then only for producing female offspring.

I put the word “worked” in quotes because there is other evidence to show that it did not work well. This study concludes “Much of this Neanderthal DNA appears to be deleterious in humans, and natural selection is acting to remove it.” The paper suggests that this was a consequence of their smaller group size- allowing more deleterious mutations to stay in the genome rather than a fundamental weakness in genes making the species jump. It bases this conclusion solely on their finding that these mutations were only weakly deleterious. That does not add up to me because the other studies showed that plenty of other mutations seemed to be strongly deleterious and thus are no longer around to be counted!

But even if the researchers got that right, it is still a consequence of humans having a sense of connectedness and sociability in a way that other hominids may have lacked. This helped us live in larger groups which helped keep weakly deleterious genes from fixing. What we know is that while these genes “worked” in producing fertile offspring in some cases, much of the load was at least mildly deleterious.

Now I say that the genes are being weeded out slowly over time, but it now appears that some of those genes which the OOA humans got from (presumably) Neanderthals was actually the ancestral condition of the gene in both species which had been lost in modern humans. IOW, the Neanderthals did not give them neanderthal genes, some of the 1.5% is simply the genes our species once had in common with them but lost being returned to us through these events. Either that or they were ours all along and returned to us through an earlier hybridization event. So even a large proportion of the “Neanderthal” genes we wind up keeping may not really have been exclusively “theirs” anyway. Thus whatever the true figure of percentage of neaderthal genome possessed by the average Eurasian, it is liable to be lower than the oft-cited 1.5%

So the scope of all the evidence indicates that successful human-neanderthal hybridization was a limited event which ended before humans obtained their present brain shape and the explosion of human culture around 36,000 years ago in the Upper Paleolithic Revolution. IOW even if what we call humans 55,000 years ago had instances where the barriers to fertility were overcome and fertile offspring were the result there is no reason to think that living humans and neanderthals, if they could be brought back, could do so. The fact that the researches in the study I cited earlier said that they could not detect any evidence of such interbreeding in living Europeans from the time humans and neanderthals lived side by side in Europe for thousands of years shows that there was no repeat of what probably happened in the mid-east 55K ago.

If any group can think outside the box, even our own boxes, its this one. Something changed in humanity in the Upper Paleolithic, and that even changed the way they interacted with other homininds. Lions and tigers have about the same fertility issues that the research indicates that archaic homo Sapiens and h. Neanderthal had, and we all know they are not the same species.

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There is debate about this in science, but you are putting forward a minority position. Long post though, can you summarize in bullet points?

Central to your point: What do you mean by “Human”?

We normally want to put those separate so they can be lightboxed. Here are the key papers you cite.

It seems you are arguing that humans = behaviorally modern Sapiens?

This is wildly overstating the scientific case. There is no reason to do so. Long-term successful Interbreeding was rare, but we do not know why. It could have been because of fertility reasons, or from cultural separation, or a combination of both. There is no evidence that the only pairing that worked is as you described.

I think your point still stands that interbreeding was rarely long term successful. Just focus on that.

That means they are Neanderthal genes, not Sapiens genes. I just do not get your point.

That is probably true.

That is highly debated. @Agauger or @vjtorley or @Alice_Linsley might jump in but there is no clear dating on an explosion of human culture (other than the rise of civilization).

Perhaps you missed my hedging terms?

Me too. But I was not claiming proof on the other, just pointing out what was said in some of the articles I cited.

Let’s say that there was an allele present in both humans and neanderthals 150,000 years ago. It is an allele shared by both species. Then over the next 95,000 years by chance it is lost from the human population. Maybe half the human sub-populations die off and they were the ones with the shared allele. This happens to genes all the time, yes? Then 55K ago the OOA group has a hybridization event with Neanderthals and picks up some genes. Among them, the allele which was originally present in both populations but had since been lost in the human population. That would count in present genetic tests as a gene from neanderthals, and in a way it is, but its also a shared gene which was originally present in both groups.

Let’s take that a step further. I think I put up a link showing there was a eastern Neandertal which died 40K ago that was found to have had human genes from another hybridization event 100K ago. That Neanderthal had human genes. Suppose those humans genes contained the allele which was originally present in the African human population but lost. Then the OOA population meets some of this neanderthal’s kin and as a result the allele is put back in the human population. Should that be counted as a “gene we got from neanderthals?” I don’t think that’s accurate, at least not without an asterisk.

I didn’t invent the term “Upper Paleolithic Revolution”. It was something scientists coined when they saw the evidence. What is new and exciting is that now we know a change in human brain shape happened at about the same time.

In a way, I see this as a bogus question. What we mean by “human” is not sufficiently precise. Instead, I see the appropiate question as:

Should we broaden the meaning of human enough so that it includes neanderthals? Or should we narrow it so that it surely excludes neanderthals?

Such question are typically settled in the culture at large, rather than at an Internet forum. In this case, it is hard to guess whether it would be settled by the scientific culture and accepted by the culture at large, or maybe the culture at large would not allow the scientists to settle this.

In any case, we clearly do not yet know enough about neanderthals.


You just made a strong case that H. neanderthals and H. sapiens were not the same species. Congratulations, that has been the accepted consensus for a while now.

Now please define what you mean by human. I contend the evidence shows that human traits go back to H. erectus about 2 million years ago.

If we are lumping things that don’t meet any of the traditional metrics to be in the same species under the “human” label, why stop there?

There are no traditional metrics I’ve heard of.

Then I suppose there is no fundamental basis to object when this Harcourt fellow says Chimps should be re-classified as human. Or Neanderthals or other of course.

Your argument is a fallacy, well known in The Parable of the Heap of Sand.

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It was meant to be. It is taking the view that lots of things that are not our species are somehow still human to an extreme in order to point out just what your fallacy is trying to imply. That just because its hard to draw a line doesn’t mean that the concept the line is trying to put a definition on does not exist. In this case if one says I am taking it to “absurd” extremes I would counter that you might think so but I did not make up the idea of classifying chimps as “human”. It was in the New Scientist article that I put up a link to.

Ironically, this could lead exactly where you once wanted to go. An outside the garden population that “evolved” and an inside an Adam that was formed. I don’t have plan where I am going with this, just throwing it out there. But doesn’t makes sense in any Christian context for “humanity” to be comprised of groups that can barely exchange genes and when they rarely do nature goes to work tossing most of them.

Look @Revealed_Cosmology the challenge is that there are several plausible definitions of “human”. You either have to define it clearly to make an argument like this, or just drop it. Of note, you haven’t even yet defined what you mean by “human”.

Instead, it seems like you are making an argument (avoiding the word “human”) that:

  1. Neanderthals and Sapiens were distinct species.
  2. Sapiens has a burst of cultural activity after Neanderthals were long gone.

Those two claims may very well be true. Even if they are true, it does not tell us if Neanderthals were human or not. The word “human” is creating confusion here.

I wouldn’t go so far as saying “Bogus”. Rather it is not a precise question.

Perhaps it isn’t. but the whole point of your “heap of sand” fallacy, and my saying “well then let’s just call chimps human like Harcourt here wants to” is that something does not have to be precise to be a real thing. It leads to an absurdity when you ignore imprecise differences just because you can’t define them precisely. We were making the same point there. We don’t have to know precisely where the line is drawn to know that there is one.

According to scripture, we are uniquely in the “likeness of God”. What does that mean? We don’t precisely know for sure though we have ideas on it. So we are like Him. Are Neanderthals like Him too? That is, are He, us, and them in that same likeness? Well since we don’t know just what that is its hard to measure directly. But there are some things we can measure. Morphology, cultural achievement, and whether or not there were barriers to reproductive compatibility. If all those things are different, it becomes less reasonable to assume this other harder to measure trait was the same. Am I making any sense to you here?

Tonight I am writing about the genetics. It seems that the barriers to hybridization between H. Sapiens and H. Neanderthal are very similar to those described between lions and tigers, and we all know that those are not the same. Are they both big cats? Sure, but behaviorally and “culturally” they are not the same animal at all. I conclude that we are not so compatible as to be of the same likeness. Maybe things were different 55K ago, but not today and not since GA was formed from the dust which bears his name.

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The above are true. And both species were human along with many other human species going back nearly 2 million years. I define human as a species with enough cognitive ability to have language, culture, and tool industry/artifacts. Every genus Homo species from H. Erectus from 2 million years ago were human based on the above definition.

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So if aliens turn up who have language/culture and industry, they would be Human??? Don’t dolphins have something like a langauge? what about ants? They don’t talk, but they do communicate with each other.

I see modern Homo Sapiens with all the traits associated with humanity as human.

They wouldn’t be human, they would be aliens who have language/culture and industry AND a genome totally unlike humans.


Neanderthals were fully human.