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I am a sun sneezer. Which is also known as having the photic sneeze reflex
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Or, the autosomal dominant compelling helio ophthalmic outbursts syndrome.
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Which basically means if I go from a dark area into somewhere that's brightly lit - You know, like, looking at the sun - I will sneeze.
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Wait for it...
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There you go, I'm a sun sneezer.
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But why does this happen?
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People have known about this effect for at least a few thousand years
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Aristotle was probably a sun sneezer because in his book of problems
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he asked: Why does the sun provoke sneezing?
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And his answer was it was the heat from the sun which causes
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sweating inside your nose, and so you sneeze to get rid of the moisture.
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but a couple millennia later
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Sir Francis Bacon demonstrated that this could not be the case because when he closed his eyes and turned towards the sun
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well he did not experience that photic sneeze reflex so his explanation was that it was the eyes
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watering and then when some of that moisture got down into the nose that caused the tickle which makes you sneeze
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but even this theory has its problems because eye watering is a much slower process than the photic sneeze reflex
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So it can't be the cause. Before I started researching sun sneezing
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I thought that having the photic sneeze reflex
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Must Convey some sort of evolutionary advantage under the people who have it. If you think about it
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Sneezing is a way of transmitting disease. In your snot there can be the living Bacteria that cause
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Tuberculosis, and strep throat or viruses that cause measles mumps Rubella and influenza, so if you're living in a moist dark cave
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and you sneeze
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Where your snot lands on the floor or the walls of the cave and those Pathogens can stay alive for hours or even days
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increasing the Likelihood of spreading that disease to other people who live with you in your cave
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Whereas if you only sneeze when you emerge from the darkness of the cave and into bright sunlight
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Well, then that mucus will quickly dry out or because it's exposed to the harmful UV rays of the sun
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It will kill all of those pathogens
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Greatly decreasing the risk of spread of disease
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By the 1960s some studies were revealing the hereditary nature of the photic sneeze reflex
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There was a father who would sneeze two times when he entered bright sunlight
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And when they tested his baby daughter who was just four weeks old
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Moving her from a dark room into full sunlight also caused her to sneeze
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Exactly two times and by the 1980s it was clear that this trait was
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autosomal dominant
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Meaning that you only needed to inherit one
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Copy of the Gene from just one of your parents in order to exhibit the trait
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But when studies the population have been done only about 18 to 35 percent of people actually have the photic sneeze reflex
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So I don't really think this gives a great evolutionary advantage, otherwise everyone would have it
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you know it could just be one of those random mutations that happens over time and
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Sustains itself because it's neither good nor bad evolutionarily speaking
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So it affects roughly one in four people
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Can you spot the person with the photic sneeze reflex?
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Nowadays, it's actually been found that the gene responsible for the photic sneeze reflex is on the second chromosome
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And it's a single letter of DNA that's been changed, on my second chromosome
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I have a C
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Where non sun sneezers have a T, and the reason that we know this is that back in 2010 there was a study of about
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10,000 people where they went online and they
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Reported whether they were sun sneezers or not and then their DNA was
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analyzed and the groups were compared and what they found was the thing the sun sneezers had in common was this one particular
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letter change in their DNA.
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That I think is pretty amazing.
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Now it's unclear exactly how this change affects your physiology and makes you more susceptible to sun sneezes
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But the best theory at the moment is that it involves the trigeminal nerve which is the largest cranial nerve it
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Involves all of the feeling that you have in your face and as the name implies
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It actually has three branches one of which receives stimuli from your eye and another which receives stimuli from your nose
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so the thought is that this really active stimulation of the optic nerve may cross over into the
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maxillary Branch causing that little tickle which gets you to sneeze
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Photic Sneezes are generally pretty harmless unless you're doing something like flying a fighter jet or performing some sort of delicate surgery.
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But this methodology,
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can allow us to learn a lot about different heritable traits and diseases just by studying lots of people and their genotypes
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This episode of veritasium was supported by 23andme. Which is actually the company that figured out that gene polymorphism
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responsible for the photic Sneeze reflex
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the name of the Company 23andme comes from the fact that humans actually have 23 pairs of chromosomes and
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The purpose of the company is to give people insight into their own DNA
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So what you do is spit into a vial
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which is actually much harder than it sounds and
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Send it off to them and of course in your saliva are some of the cells from your mouth
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They analyze the DNA from those cells
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And then they send you a report where you can find out tons of stuff about your genes like
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Where do your genes come from that is what's your ancestry and do you have the photic sneeze reflex? Do we share the same?
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Change of DNA on our second chromosome you can also learn about your health and other physical traits and how much
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Neanderthal you are so if you want to learn more about your genotype
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Then you should go to 23andme.com/veritasium, so I want to thank 23andme for supporting me
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And, I want to thank you for watching.