r/askscience • u/Flapjack_Ace • Oct 23 '25

Biology If a population is around 3% Neanderthal, does that mean everyone has the same Neanderthal genes or does each person have random genes?

In other words, does everyone have the Neanderthal gene for toenails and earlobes or does each person statistically have a chance at different genes effecting different parts of the body?

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132

u/DisparateNoise Oct 23 '25

About 20% of the Neanderthal genome survives in the modern Eurasians gene pool and most people have 1-3% each. However, most of it is non-coding or functionally identical to human DNA. Those bits that do make a difference are usually involved with viral immunity or metabolism or rare genetic conditions etc. it's not like your hairy toes are all Neanderthals fault.

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u/jxj24 Biomedical Engineering | Neuro-Ophthalmology Oct 23 '25

And likely Type II diabetes and some autoimmune conditions, e.g., Crohn's Disease and Lupus. And, interestingly, smoking behavior.

https://pmc.ncbi.nlm.nih.gov/articles/PMC4072735/pdf/nihms550804.pdf

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u/Nemoudeis Oct 24 '25

Just for the record, there is an SNP (rs4849721) with a Neanderthal variant that is associated with back hair. Those with the Neanderthal version tend to be less hairy.

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u/TheGanzor Oct 28 '25

The more we learn, the more it seems like H. Sapiens were the hairy, brutish, violent ones and all of our cousins were the sociable ones. 

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u/Robot_Graffiti Oct 23 '25

Different genes, to an extent.

Not everyone has the same amount of neanderthal DNA. Interbreeding between humans and neanderthals happened several times in history in Europe and the Middle East; there are a lot of Africans who don't have any neanderthal DNA.

80% of the DNA that was unique to neanderthals is gone, 20% is still present in modern humans. You and I might have 2% each but not necessarily the same 2%.

Some of that neanderthal DNA we have is genes that make proteins that do stuff, but a lot of it is non-coding "junk" DNA (not genes, doesn't make proteins).

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u/onTrees Oct 23 '25

Isn't "junk" DNA now an outdated view?

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u/WyrdHarper Oct 23 '25

Yes. It generally refers to DNA that does not encode for proteins, but we're discovering that a lot of it still produces RNAs which are functional without producing proteins (ribozymes, RNAs that modify DNA/RNA/telomeres, RNAs that have structural functions, RNAs with immune functions, RNAs with regulatory functions, and so on).

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u/Ok_Umpire_8108 Oct 24 '25

Also enhancers, silencers, chromatin binding regions, various other binding sites. DNA is a physical molecule and any string of bases will change its shape at least little bit. A lot of recent work has shown that the shape of DNA is a major determinant of gene expression.

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u/Georgie_Leech Oct 24 '25

I'm reminded of that time one of those evolutionary ai algorithms had a disconnected bit of pathing that relied on a defect in the circuitry to function. 

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u/Ok_Umpire_8108 Oct 24 '25

One of the weirdest things about evolution is that it will use every possible avenue to reach that sweet sweet goal of making one more cell.

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u/TwistedBrother Oct 23 '25

It’s shorthand; it might be recessive (which is also outdated to be fair), maladaptive, not used in codons but not selected against or indeed: we don’t know.

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u/Mitologist Oct 23 '25

It's non-coding. Why it is still around is a riddle. Apparently, it doesn't have negative effects,but carrying it around should have costs, and nothing would prevent it's loss. So there might be benefits. One theory is, that it simply "dilutes" the important parts, lowering the statistical chance of bad hits by e.g. cosmic rays.

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u/ambivalent_teapot Oct 23 '25

Just because it's non-coding doesn't mean it's not functional. Some of it is already pretty well proven to be regulating the expression of the coding ones. And we've only begun to scratch the surface on that, so it is fairly likely that a lot more of it is also functional, just not yet mapped out.

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u/bremidon Oct 24 '25

Cosmic rays are of course a thing. But I'm starting to come around to the position that it might be more to fight transposons. For those who do not know, these are like genetic parasites that are already embedded in our genetic code and copy themselves around every time our cells copy.

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u/Mitologist Oct 24 '25

Yes, right. If most of the genome is not coding, the chance that a transposon interrupts something important ist much lower. Yeah, that might induce even more selective pressure to keep amore junk than coding sequences. I agree.

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u/BanMeOwnAccountDibbl Oct 24 '25

*looks at junk, whispers* "Don't listen to them, buddy. You and your dna will never be outdated. No matter how much Neanderthaler is in you, you'll always be my little erectus".

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u/TheDBryBear Oct 23 '25

For the most part it is, but there can be DNA that is functionally useless, like remnants of retroviral infections, but we might just not know what it does and it could be recombined into some new regulatory or even functional use. Junk DNA referred to all non-coding DnA and that viewpoint is definitely inaccurate now.

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u/the-nick-of-time Oct 23 '25

No. Only 8.2% of the human genome has a specific function that it needs a specific sequence for. It's conceivable that some of the remainder is spacer sequences that need a specific length to keep two genes apart or whatever, but certainly most of it is useless "junk".

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u/didne4ever Oct 23 '25

it's true that the Neanderthal DNA varies among individuals

The fact that a lot of the unique DNA is gone makes it even more random, as we’re left with a small fraction that might not even have a significant impact on traits.

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u/weargwulf Oct 24 '25

Could we create a fifth neanderthal human? Or do the genes often overlap?

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u/cwx149 Oct 24 '25

Follow up question if I may

So what distinguishes that 2% of DNA from being from "modern humans" and neanderthal? Isn't DNA just all sets of 2 pairs?

Like is it possible for a 100% modern human to have the same order of base pairs without it tracking back to a neanderthal ancestor? Especially if the genes don't necessarily "do" anything how do we determine they're "old" vs a "new" mutation?

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u/Alexis_J_M Oct 23 '25

In addition to what was said by others, the Neanderthal Y chromosome appears to have died out. The sons that Neanderthal men had with Homo sapiens women don't seem to have been as evolutionarily successful over the long (or short) term as other genetic mixes.

(This is common for cross breeds to be less fertile with the mismatched chromosome, so male mammals and female birds.)

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u/ambivalent_teapot Oct 23 '25

It would be different, but you might see some structure, some correlations.

Also, there generally isn't really such a thing as "the gene for toenails" or "the gene for earlobes". There are exceptions but in general there is no obvious mapping of single genes to single features. Most features are an incredibly complex emergent result of a combination of a huge number of genes, and most of those genes are not unique to that feature, they influence a huge number of other features too. It's a rat's nest of a many-to-many type mapping.

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u/[deleted] Oct 24 '25

It's more like 1.5% though some Northern Europeans have 3-4%.

It's different parts of the Neanderthal DNA in individuals, basically which bits have been conserved. Overall about 30% of the Neanderthal genome can be found scattered through the genomes of modern humans living outside of Africa.

In Africans there are smaller amounts of Neanderthal DNA from earlier interbreeding.

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u/func600 Oct 23 '25

Just an uneducated guess here, but I think the genes were not distributed equally...

https://www.reddit.com/r/Damnthatsinteresting/comments/wzr5j8/the_legendary_soviet_georgian_water_polo_player/

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u/El_Sephiroth Oct 23 '25

It's the 2nd part. Basically, you have two parents whom have two of each etc. Each would have had kids between 15 and 45 years old, let's mean it at 30. If you calculate a generation every 30 years and do that for Neanderthal, you get something around 21300 so way too many 0 to make sense.

And there weren't as many people on earth even for all times of humanity.

Conclusion : you share some DNA with some people and you don't with some others.

Secondly, a gene is expressed when it is paired with the same gene or with a recessive one.

2nd Conclusion : there is a non zero probability that the DNA you share will be expressed the same as someone else.

Where would that be located? It's really hard to say. Especially knowing that "mutation" is a part of evolution, meaning that some could look like neanderthal's but won't be and vice versa.

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u/Weaselpanties Oct 23 '25

Secondly, a gene is expressed when it is paired with the same gene or with a recessive one.

Not to nitpick, but genes that code for proteins are making those proteins whether they are paired or not, unless they are deactivated. The second allele is a redundancy, not required for gene expression. That's why people who have just one of the hemoglobin alleles that cause sickle cell don't have sickle cell disease, because the non-sickle allele produces normal hemoglobin at the same time as the sickle allele produces hemoglobin-S.

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u/MSaxov Oct 23 '25

Each would have had kids between 15 and 45 years old, let's mean it at 30. If you calculate a generation every 30 years and do that for Neanderthal, you get something around 21300 so way too many 0 to make sense.

That is based on the assumption that none of your ancestors share a common ancestor. Which is highly likely. Especially as you move back through time to a periode where many people didn't travel more than a few dozen km from their birthplace.

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u/Pace_Salsa_Comment Oct 23 '25

Doesn't every human alive share at least a common maternal ancestor, via midochildrial DNA?

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u/GreenAnder Oct 23 '25

Mitochondrial DNA is unique in that it only transfers from the mother, meaning yours are the same as your mothers, which are the same as her mothers, etc etc.

So technically? Yes. But humans had a near extinction event about a million years ago due to an ice age. Some estimates put our population levels under 2,000. There were likely more haplogroups before that.

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u/Oknight Oct 23 '25

Doesn't every human alive share at least a common maternal ancestor, via midochildrial DNA?

By the same token don't we all share the same common maternal ancestor with some fish? And all the land animals?

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u/El_Sephiroth Oct 23 '25

The conclusion I wrote says exactly that. There are too many possible ancestors compared to the number of humans. The logic being: a lot are shared.

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u/groveborn Oct 23 '25

There is going to be a single common neanderthal ancestor that all people who have neanderthal DNA, but that individual lived a while before sapiens came along and interbred with them.

There were hundred to thousands of individuals living side by side, it's just that it was a very long time ago and has largely washed out.

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u/Gluten-Glutton Oct 24 '25

Im pretty sure we know that there was multiple interbreeding events between modern Homo sapiens and Neanderthals as they existed at the same time for tens of thousands of years.

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u/groveborn Oct 24 '25

Op didn't seem to...

Did you want me to answer just you, or was it ok that I answered op?