If a time machine were created, and we used it to steal a newborn Neanderthal, then give it to a volunteer to raise, what would become of it?

Could it learn English, and possibly even have children? Or would it eventually figure out it's not completely a human?


Well, let's starting quoting something from wikipedia:

The Neanderthal skull is typically more elongated and less globular than that of anatomically modern humans, and features a notable occipital bun.

Neanderthals are known for their large cranial capacity, which at 1,600 cm3 (98 cu in) is larger on average than that of modern humans.

Evidence suggests that Neanderthals walked upright much like modern humans.

Larger eye sockets and larger areas of the brain devoted to vision suggest that their eyesight may have been better than that of modern humans.

Neanderthals made stone tools, used fire, and were hunters.

However, rates of cranial trauma are not significantly different between Neanderthal and middle paleolithic Anatomically Modern Human samples. Both populations evidently cared for the injured and had some degree of medical knowledge.

The genomes of all non-Africans include portions that are of Neanderthal origin, a share estimated in 2014 to 1.5–2.1%.

Now, I'll answer your questions:

If a time machine were created, and we used it to steal a newborn Neanderthal, then give it to a volunteer to raise, what would become of it?

He/she would be raised as an otherwise normal boy or girl. Perhaps with some odd-looking traits, but normal otherwise.

Could it learn English?

Yes. And Spanish. Also French. Mathematics. Chemistry. Medicine. Computer programming. Economy. Chess. Driving vehicles. And so on...

Gosh, given the fact that neanderthals had a larger brain than modern humans, it is very possible that in fact they were more intelligent and smarter than us (or perhaps not). I think (but I might be wrong) that it is very likely that a median neanderthal would outperform a median modern human in many mental skills tests if both were to be raised in the same modern society and given similar education.

And possibly even have children?

They did.

Or would it eventually figure out it's not completely a human?

Stop being racist! Neanderthals are/were completely humans!

They can and in fact did interbred with modern humans, so this clearly shows that they and us are members of the same species.

We already have enough genetic, antropologic and archeologic evidence to firmly set that the Neanderthals are/were completely humans, whatever is a reasonable definition of "completely human". Saying that a Neanderthal is not completely human is not really different than saying that black people are not completely human. But, I don't want to accuse anyone here (including the OP, which probably was not aware of those facts). I just want to clear out the confusion and conscientize people to abandon the stereotype of seeing neanderthals as apes, subhumans, "not completely humans" or anything alike.

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    $\begingroup$ They are definitely human in the sense of species of the genus Homo, so were Homo Habilis. The term is Speciest, in the context of 'Stop Being ...'. A larger brain does not imply that they are capable in the sense that Homo Sapiens are capable (or even the reverse). That they have language, dexterity, planning, and care is apparent from the evidence. The part about Neaderthals that is unknown is cultural change. The Homo Sapien population's culture started radically altering over short time scales about 200 000 years ago. Whether Neaderthals had a similar capacity is unknown. $\endgroup$ – Kain0_0 Apr 10 '19 at 7:58
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    $\begingroup$ @Kain0_0 No the term is not speciesist (I corrected the word here) because Homo Sapiens Sapiens (that's us) could breed with Neanderthals. That means we and they are the same species. However, you are correct their capacity for cultural change is unknown, but it is not unreasonable to assume it might be comparable to ours. $\endgroup$ – a4android Apr 10 '19 at 11:53
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    $\begingroup$ @kain0_0 A lot of what you said is wrong, including the 'correction' around terminology. Neanderthals were not a seperate species. They were Homo sapiens neanderthalensis, meaning a subspecies, or a race. What we call 'race' today is akin to spots on a dog, and is a far cry from anything resembling biological race. Neanderthals, by contrast, are a better representation of race. The proper terminology of subspecies rather than them being a seperate species is especially borne out by the ability to conceive viable offspring with cro-magnon. $\endgroup$ – user49466 Apr 10 '19 at 11:58
  • $\begingroup$ I don't believe it is racist to question "humanness" of Neanderthals if you do not have sufficient information about them. There are species distinct from Homo sapiens that are inherently, say, faster than Homo sapiens. If you don't know anything about Neanderthals, it is OK to assume that they are inherently different (until you gather enough information to form a more accurate conclusion). Given that in most modern societies racism is considered a serious misdeed, one should not falsely accuse another of racism. $\endgroup$ – user63092 Apr 10 '19 at 12:26
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    $\begingroup$ @KainO-O I have imagined a highly intelligent fictional character or two, who thinks that it is inconsistent for humans of ordinary intelligence levels to make a big deal about the relatively minor intelligence differences between ordinary humans and apes, proboscideans, and cetaceans while at the same time expecting the highly intelligent character to treat ordinary humans as people despite the vast difference in intelligence. Human variation seems greater than the average difference between humans and many other animals, let alone Neanderthals. $\endgroup$ – M. A. Golding Apr 11 '19 at 19:47

A Neanderthal might be a little funny-looking, but they were close enough to modern humans that you couldn't really tell. There are no physical or mental qualities shared by Neanderthals that do not exist in modern humans; the only differences are averages, and the Neanderthal average overlaps with the modern human average in all qualities.

Example: On average, Neanderthals had large noses compared to modern humans, but there are some humans around today with pretty big schnozes, so you couldn't prove they were a Neanderthal just by measuring the size of their nose. Same goes for their size, shape, voice, mental capabilities, and so on.

A Neanderthal in modern times would be able to get along just fine, though they might have a bit of difficulty getting a date. A scientist who happens to know the typical Neanderthal characteristics might be surprised by how much the guy walking down the street looks like a Neanderthal, but there would be enough doubt that they probably wouldn't mention it. Only a genetic test would prove there was something weird going on.

There may be some fertility issues between Neanderthals and modern humans, but not significantly more than what many couples experience today. Modern medicine may even make interbreeding more viable.

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    $\begingroup$ Last year, there was a day that I were surprised to see walking in the street, a woman that had a lot of traits very similar to what I would expect from a neanderthal. Pale skin, blonde-red hair, strong barrel-like body (much stronger than what most women are, without being fat), large nose, large head, large eyes, sloped forehead and some other strange face traits. Of course, that was probably a coincidence, but shows up that a true neanderthal walking in the street would not be perceived as anything uncommon. $\endgroup$ – Victor Stafusa Apr 10 '19 at 8:01
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    $\begingroup$ The right scientist might actually ask the Neanderthal suspect out on a date! $\endgroup$ – elemtilas Apr 10 '19 at 13:05

Strictly speaking. It would be obvious right away.

Much larger nose, shorter frame, altered pain sensitivity, and different vocal chords.

A Neanderthal would definitely be able to learn to understand English, at least the direct parts of it. It may even be able to speak it, though we would probably perceive an accent.

There may be some difficulty with the more ingenuitive activities that we take for granted, such as mathematics, cinema, or bridge design. Over the course of their reign in Europe Neanderthals did not appear to develop new technologies, or substantially change culturally. This might be explicable by the general difficulty of survival curtailing such developments, or by a genuine difference. There isn't a clear answer.

As for children, a Neanderthal would be compatible, particularly with those of European descent. Most Europeans are in fact hybrids of early Homo Sapiens and Neanderthals being about 3%ish Neanderthal. As to which Neanderthal sex is most compatible with modern humans is itself an open question.

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    $\begingroup$ Where does the altered pain sensitivity come from? $\endgroup$ – L.Dutch - Reinstate Monica Apr 10 '19 at 9:49
  • $\begingroup$ Perhaps this: smithsonianmag.com/science-nature/… where they muse that they suffered a lot of trauma and injuries, but still lived fairly long lives. $\endgroup$ – Juha Untinen Apr 10 '19 at 10:52
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    $\begingroup$ There's actually some debate as to whether Neanderthal is even a seperate species (H. Neadethalis) or a subspecies (H. Sapian Neandethalis) (I probably got the spelling wrong) but in the later case, Humans and Neanderthals would be fully compatible (Like how a Great Dane and a Chihuahua are genetically compatible because they are both the same species (Canis Familiaris). There are of course, some other limitations preventing the two dogs from breeding, genetics is not one of them.) $\endgroup$ – hszmv Apr 10 '19 at 12:10
  • $\begingroup$ @hszmv this is a really good point. "What is a Species?". Coyotes and dogs descended from Wolves can and do interbreed, though they do so rarely because they have very different habits, even though they diverged over a million years ago. $\endgroup$ – Ben May 15 '19 at 19:46
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    $\begingroup$ @aCVn Interesting point. Technically speaking DNA from any two Eukaryotic Cells can be mixed together. The chemistry is identical and all of the basic molecules are identical. How they are assembled is the problem. Take any two books and pull out alternating pages from both books and stitch them together. If the story makes sense it is a success. However each unmarked chapter, poorly formed sentence places the new story close to death or actually dead. Ideally this process should be handled to ensure maximum chance of success, or at least until the new story has a chance to make more. $\endgroup$ – Kain0_0 May 21 '19 at 0:31

TL;DR: In appearance, Neanderthals may look very different from "us", whoever "us" refers to, but then we look very different to each other.

Imagine in the pre-television era, the thoughts of a south-east-Asian peasant encountering Gerard Depardieu: "What is this strange, hulking creature?"

I suspect if we met a Neanderthal, we would not think him the most odd looking person we saw that month.

In terms of reproduction, Neanderthals could certainly breed with modern H. Sapiens, but it's not clear to what extent the offspring would be fertile. I suspect they would do just fine, but this is not actually known.

Long version

There is no bright line delimiting what differences between groups constitute them as two species, versus two subspecies.

Generally if two groups are incapable of mating and producing viable offspring, they are clearly separate species, but there is a considerable range of possibilities between species which cannot interbreed, and subspecies which are visibly different, and perhaps rarely interact, but are capable of interbreeding freely if the occasion arises.

For example, lions and tigers can interbreed and the offspring are generally fertile, though the second generation is often of delicate health. However they generally do not interbreed because their ranges do not overlap, and their habitat and lifestyle are different. So this is an example where the speciation process is almost complete.

The notion of "what is a species" is politicised, because the concept is used in conservation law. Therefore there are powerful incentives to classify two groups as separate species or as mere subspecies, in order to give an endangered group the protection of the law, or to deny it to them as a mere subspecies. These powerful social forces make it difficult to come up with any objective definition of the distinction between "species" and "subspecies".

It's not really known where in this range falls the distinction between Neanderthals and Homo Erectus.

  • They are possibly simply a racial group, capable of interbreeding freely, producing offspring with a combination of characteristics from the parents.
  • But it's also possible they are more akin to the Lion/Tiger example above, where interbreeding is possible, but the offspring are not necessarily particularly successful.
  • If the offspring are partially fertile, then a female hybrid is likely to be more successful in reproducing than a male, based on Haldane's rule: https://en.wikipedia.org/wiki/Haldane%27s_rule

For comparison, Coyotes and Wolves (and domestic dogs) diverged over twice as long ago as Cro-Magnon Man and Neanderthal Man, and they interbreed just fine. So it seems likely to me that reanimated Neanderthals would have no difficulty interbreeding with modern humans.

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  • $\begingroup$ "Imagine in the pre-television era, the thoughts of a south-east-Asian peasant encountering Gerard Depardieu: "What is this strange, hulking creature?"" [resists urge to Google "Gerard Depardieu fan club" & then post links to this on any sites found so he can enjoy the subsequent storm of outraged posts & doxing] ;D $\endgroup$ – Pelinore Apr 10 '19 at 17:38


It has already happened.

When anatomically modern humans dispersed from Africa, they encountered Neanderthals in Europe and Asia.

This left a signature in our genomes — with about 2 percent inherited from the Neanderthal. This DNA influences our immune system and the diseases we develop.

Initially, it was thought only a single episode of interbreeding between modern humans and Neanderthals occurred.

But East Asians have up to a fifth more Neanderthal DNA compared to Europeans — suggesting the possibility of many encounters.


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Except what was already said about brain size, tricky reproduction and weird outlook, it would lack a few modern evolutionary adaptations:

  • no lactose tolerance after childhood
  • no alcohol tolerance
  • weak immune system in relation to modern viruses / bacteria
  • poor ability to cope with excessive amounts of food

At least he would be expected to suffer from all problems of uncontacted tribes, if not worse.

Oh... and quite many Neanderthals whose DNA were analysed, clearly were suffering from mild inbreeding.

So such problem plus, presumably, because of outlook risking being considered as celebrity and being expected by tabloids to show some stone age skills, in spite of being brought up by some modern, middle class family. ;)

With IQ the issue is not directly researched yet. As mentioned, Neanderthals seem to be technologically a rough match for their contemporary Homo Sapiens. Technically speaking they had a bit bigger brain, while among Homo Sapiens there is actually weak (0.3-0.4) correlation between IQ and brain size.

There is a tricky to measure (and ideological landmine field) issue whether not only our culture, but also underlying genome responsible for neurology evolved a bit from neolithic revolution onward to be more compatible with civilisation. [Well, there is this awkward issue of surprisingly persistent differences in IQ among ethnic groups, yes I know I should say its discrimination, culture and unfair tests... OK, so Neanderthals would face discrimination and culturally unfair tests.] In evolutionary biology there is contention to what extend the evolution is gradual, and to what extend its actually dominated by punctuated equilibria. Pending where one would place those key evolution changes, his IQ should be comparable to modern humans or he should be facing learning difficulty when facing more abstract concepts.

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  • $\begingroup$ "no lactose tolerance after childhood" Isn't that pretty common in people not of recent European ancestry? $\endgroup$ – a CVn May 20 '19 at 9:48
  • $\begingroup$ @aCVn India (you may call Preindoueropeans as European ancestry, but not recent...)? Arabian Peninsula? Western Africa? $\endgroup$ – Shadow1024 May 20 '19 at 15:58
  • $\begingroup$ I don't know, but it's something I distinctly recall hearing something along the lines of; hence the question mark at the end of my comment. $\endgroup$ – a CVn May 21 '19 at 6:07
  • $\begingroup$ @aCVn Lack of lactose tolerance for adults is the natural state. Nevertheless in last 20k years at least in half dozen of populations there has been an evolutionary favoured mutation allowing for its digestion by adults. $\endgroup$ – Shadow1024 May 21 '19 at 6:36

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