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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 called 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 red-headedness
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 to 2 percent of the world population
and they don't have red hair because they stole hell fire 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 one receptor, or MC1R gene.
We all have it nestled on our chromosome 16,
but your red-headed 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 pheomalinin, you're gonna have reddish or blonde 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.
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 red-headedness
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 kinda 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 Health
found that redheads are actually more sensitive to thermal pain, or excessive heat and cold,
and that they actually required, on average, nearly 20 percent 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,
four percent of the population actually has red hair, perhaps thirty percent still carry that gene
keeping the potential for ginger generations alive and not just in the UK.
So rest assured gingers are gonna 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.
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And go to YouTube.com/SciShow and subscribe.
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不為人知的紅頭髮秘辛 (The Truth About Gingers)

22522 分類 收藏
羅紹桀 發佈於 2016 年 4 月 25 日    劉采翎 翻譯    Kristi Yang 審核
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