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Hank Green: You know, redheads take a lot of crap, not only do they fall prey to nicknames like Big Red, Rusty, and Daywalker, they also carry a rich history of misunderstanding on their frequently freckled shoulders.  In Greek mythology, it was said that redheads turn into vampires when they die.  Egyptians particularly enjoyed burning ginger virgins, and a number of alchemist spells call for the fat of a flame-haired man.  If that weren't enough, in recent years there have been headlines suggesting that redheads will actually go extinct within this century.  A lot of the ignorance surrounding redheadedness probably has to do with the fact that although they aren't very rare, redheads aren't very common either.  Though certain countries like Ireland and Scotland seem to be hosting perpetual Weasley family reunions, gingers only make up about 1-2% of the world population, and they don't have red hair because they stole hellfire or were conceived during menstruation or bitten by a werewolf as a baby.  They get their coppery hue the same way we all get our coloration, from melanin.  

Hair color is a genetic trait associated with the melanocortin 1 receptor, or MC1R gene.  We all have it nestled on our chromosome 16, but your redheaded friends possess a mutated version of it.  This gene gives instructions for making protein receptors located on our melanocytes, the special cells that produce melanin.  Melanin is what gives our eyes, hair, and skin their distinct hue, and it comes in two varieties: eumelanin and pheomelanin.  A person producing mostly eumelanin will have darker hair and skin that tans easily and is better protected from the sun's UV radiation.  But if you're brewin' mostly pheomelanin, you're gonna have reddish or blond hair, fair skin that burns easily because it's not naturally protected from the sun.  That's why fair folk have an increased risk of skin cancer.  It's that MC1R gene that dictates what kind of melanin you get, and if the gene is activated, you'll end up with more eumelanin and will be darker complected, if those receptors don't trigger, your cells pump out the fair pheomelanin.  We're not exactly sure just how far back the trait goes, but scientists recently extracted a version of the ginger gene from the remains of two neanderthals, indicating that at least some of them were redheads.  However, the gene was a variant, not the one present in modern humans, indicating the mutation evolved independently from human redheadedness in an example of convergent evolution.  

Now you may be wondering why both humans and neanderthal genes would perpetuate a skin type so prone to sunburns.  Well, it has to do in part with geography.  People from equatorial regions usually have darker hair and skin to better protect them from the sun's radiation, whereas fair skin and hair is more prevalent in northern areas with lower levels of sunlight.  The farther you move from the equator, the more that selective pressure for darker pigmentation lessens, and the mutant MC1R genes are not selected against, so they can spread throughout a population.  And then, hello Scotland!  The successful spread of this mutation may be because fair skin is better at generating vitamin D, which could have actually given flame hairs an evolutionary advantage in the perpetually cloudy North.  

But you may have also heard that gingers are kind of babies when it comes to pain, and I hate to say it, but there's some truth to that.  A couple of studies funded by the National Institutes of Heath found that redheads are actually more sensitive to thermal pain or excessive heat and cold, and that they actually required, on average, nearly 20% higher doses of anesthetic than their dark haired counterparts.  And researchers aren't entirely sure what's going on here, but one hypothesis connects pain tolerance to that tricksy MC1R gene, since the gene is responsible for the receptors of pigment producing hormones, they may also interact with similar molecules like endorphins, our body's natural painkillers.  

And finally, what about that great imminent ginger extinction?  That, I can tell you is bogus.  Yes, the mutation is a recessive trait meaning that both parents have to carry the allele or gene variant for it to produce a red-haired offspring, but that still means that even if say, 4% of the population actually has red hair, perhaps 30% still carry that gene, keeping the potential for ginger generations alive, and not just in the UK.  

So, rest assured gingers are going to be passing along their genes and supporting the sunscreen industry for a very long time.  Thank you for watching this SciShow Dose and a big thanks to our subscribers on Subbable, without whom you would not be watching this.  Would you like us to tweet you a picture from our beautiful studio or add your custom message to our Doobly-Doo?  To learn more about these and other exclusive perks, go to subbable.com, and if you have an idea you'd like us to cover or a question or comment, leave it for us in the comments below, and don't forget to follow us on Facebook and Twitter, and go to youtube.com/scishow and subscribe. 

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