Lots of us have quirks that seem to run in families, like being left–handed or sneezing when you eat peppermint.

And as long as it’s not something like having extra wide feet that you need custom shoes for, like me it’s fun to think about the first member of your family a few hundred years ago to have that weird characteristic. But some traits are much older.

Like, if you and your whole family are all morning people, you might be able to trace that particular trait way, way back to an ancestor you might not expect. Because they’re a Neanderthal. [Music] Long before SciShow, or YouTube, or even the first modern humans, the Neanderthals were happily living in what’s now Europe and Asia. These stocky, archaic hunters are known for their wide frames and strong brows.

They first appeared around 400,000 years ago and they went extinct about 30,000 years ago. And those dates are important because Homo sapiens, AKA our species of human, only popped up in Africa around 300,000 years ago, and only made it into the same regions as Neanderthals roughly 80,000 years ago. So there was a pretty short window of time for our species to swipe right on their Neanderthal neighbors.

But boy, did they. Even though their lineages split around 600,000 years ago, making them two totally distinct species, they didn’t seem to have any trouble making perfectly healthy offspring with each other. For those of you flashing back to high school biology, here’s a quick explanation.

It’s rare, but two individuals can still be from different species and produce fertile offspring. Essentially as long as there wasn’t widespread interbreeding, and there wasn’t, …then they can still be considered two distinct species, and that doesn’t prevent them from having fertile hybrid offspring, with a hybrid genome to match. Which leads us to today, where most people with European or Asian ancestry have between 1 and 4% Neanderthal DNA in their genome.

And that sounds like a lot, which would make it seem like these cross-species couples were happening like, all the time. But some models suggest that you could get this much Neanderthal DNA in the human genome with just a single coupling per generation over the time that they coexisted, meaning that Neanderthal-human hybrids were still pretty rare. And while some of the genes they gave us may have been beneficial, others, not so much.

We’ll start this list bright and early, with the genes that might make you a morning person. It seems like some people are just wired to be able to wake up before their alarms and be that early bird. And it turns out that that might just be literally written into their genes.

A study published in 2023 in the journal Genome Biology and Evolution scrutinized the human genome looking for anything that might affect the circadian rhythm, called the chronotype for short. They found several genes that may mess with someone’s chronotype, and suspected that some of those were introduced by Neanderthals, a suspicion the researchers confirmed when they compared the present day human genome with the Neanderthal genome. After looking at some genome-wide association studies, they found that the Neanderthals had mostly morning-people genes.

Now being a morning person isn’t just good news for those of us who have to wake up for a 7am shift. These genes essentially give you a shorter, more flexible circadian rhythm that can match up to changing daylight hours throughout the year. That makes these early bird genes good for anyone who lives in a place where daylight hours get longer in the summer and shorter in the winter.

Meaning this gene was pretty beneficial, even without the 9 to 5. And rising with the morning sun isn’t the only way that Neanderthals adapted to living further north. They also had some major shifts in their immune systems.

See, the basis of immunity in mammals is built on something called the major histocompatibility complex, or MHC. For humans the MHC is coded on specific genes called HLA genes. And these genes are in charge of a bunch of stuff relating to immunity, including different MHC proteins that display pathogens for our immune system to target.

What all that alphabet soup means is that the more alleles, or versions, of the HLA genes we have, the higher the chances we can effectively present, and therefore target, pathogens. So imagine our luck when  our Homo sapiens ancestors came across Neanderthals with all kinds of fun HLA variations. A paper from 2011 identified  several specific HLA alleles, like one named HLA-B*73.

Geneticists always give  things the catchiest names. That, along with other HLA variants, essentially let early Homo sapiens copy their friends' homework, immune-system wise. And what’s wild is that this gene may not be Neanderthal after all.

The researchers think that it originated in a different hominin species called Denisovans, who lived primarily in Asia. We know that Neanderthals, Denisovans, and humans all intermixed, so whether this gene got to humans directly from a Denisovan or via a Neanderthal is anyone’s guess. But either way, this exchange meant that all of the immune system advantages that they had built up over the years made their way right into the modern human genome.

And once these alleles were introduced to our genomes, they did a really great job at protecting us, meaning that they got more and more common through the generations. And today, they code for more than half of our HLA genes. Neanderthals introduced us to other immune boosting genes too, like ones that change our response to influenza A virus.

Researchers believe these kinds of genetic changes to our immune systems helped our ancestors adapt more quickly to the European environment and climate. So if you have a strong immune system, you might have Neanderthals to thank for that. But if you were starting to feel like the Neanderthals genes were all just sunshine and rainbows, then think again, because this is one gene mutation you won’t be thanking them for.

Most of us don’t like pain, but how well people can tolerate that pain varies a lot. We usually refer to this as a pain threshold, and it pretty much determines whether or not we cry when we step on a Lego. Or something like that.

But if you’re like me and you cry from stepping on a Lego, that sensitivity could be written into your DNA. A group of researchers studying the SCN9A gene identified several variants that affected people’s sensitivity to pain. And from looking at a ton of genome data, they found that some of those variants were linked back to Neanderthals.

So in the name of science, the researchers investigated how these variations affected  people’s pain thresholds. Don’t worry, no Legos were used in this procedure. And they found that having  the Neanderthal mutations actually increased sensitivity to pain, which means lower pain thresholds and more painful wounds.

But this isn’t as bad as it sounds. Being more sensitive to pain can help you avoid injury, since you’re gonna bail out of a painful situation before anything gets permanently damaged. So if you cry when you stub your toe, its ok!

That jolt of pain may have kept your ancestors alive Thank you for supporting SciShow by watching, commenting, and telling people about us. And if you got yourself a 2025 Complexly Calendar, thanks for supporting SciShow that way too! Complexly Calendars are all about bringing together Complexly’s shows in one piece of merch.

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But we’re only making a limited number, so get them while you can at Complexly.store/calendar or the link in the description. Those first three traits we’ve talked about came to us via Neanderthal genes, but that’s not the only way that Neanderthals have contributed to our genomes. There are sections of DNA called single nucleotide polymorphisms, or SNPs, and we have some that can also be linked back to interbreeding with Neanderthals.

And these sections of the genome are connected to some surprising human conditions. For example, a study from 2024 found many SNPs of Neanderthal origin that significantly increased a person’s chances of having autism. They also found several SNPs that weren’t implicated in autism, but likely associated with common comorbidities of autism, like epilepsy.

A separate study found that Neanderthal SNPs could explain a significant degree of risk for depression. On its own, that doesn’t really make a ton of evolutionary sense. But that study mentioned that these SNPs were found in some expected places, like genes associated with neurological diseases, and some less expected places, such as genes linked to circadian rhythm.

Which means these might have basically hitched a ride along with a more beneficial gene, and just happened to stick around. The 2024 paper also suggested that these genes may have persisted to today's humans because of a genetic bottleneck in the Neanderthals, but both of these are just hypotheses. And just to be clear: if you’re autistic or have depression, it doesn’t mean you got too much Neanderthal DNA or anything, just that the specific Neanderthal mutations you did get may have increased your predisposition to these things.

So we’ve talked about some traits that can be traced back to  our Neanderthal ancestors. But as a bonus, let’s talk about one gene we know we didn’t get from them. Red hair.

See, we know from other genetic studies that there were some red headed Neanderthals. And those same studies tell us that the Neanderthals had a totally different mutation that got them there. We all have a gene called melanocortin 1 receptor or MC1R, which is partially in charge of pigmentation in both our skin and hair.

And there are certain mutations to the gene that result in less pigment being made, which gives you pale skin and red hair. So naturally, researchers got curious about whether Neanderthals had any mutations to give them a similar look too. They were able to find this same MC1R gene in Neanderthals, but the mutations they found in their pigmentation gene were different from what’s found in our pigmentation gene.

And it’s not like they didn’t check or anything. They looked at around 3700 human MC1R genes, and they couldn’t find the Neanderthal mutation in any of them. Beyond that, the Neanderthal mutation would also have decreased the gene’s functionality, which means there probably were some redheaded Neanderthals walking about a hundred thousand years ago.

But they got that way completely independently from homosapien redheads. Even though they’ve been extinct for thousands of years, the Neanderthals that our ancestors knew and loved are still around, in a manner of speaking. Just like you’ve got grandma’s nose or your dad’s sweet tooth, you may be able to say your cold-fighting or early-rising comes from your ancestors, too.

It just goes back a little farther than you might think. [ OUTRO ]