In the vasttimeline of humanity, blue eyes are relatively new. Originally, everyone wasbelieved to have had brown eyes. It wasn't until about 10,000 years ago that blue eyed people startedpopping up everywhere. It was probably creepy as (beep). Today it's estimatedthat somewhere between 20 and 40% of Europeans have blue eyes.
So what the heck happenedé Where'd all these blueeyed people come fromé Short answer, genetic mutation. (scary music) Here's a quick breakdown: Eye color is determinedby the amount of pigment you have in your irises. If you have a lot ofpigment, you have brown eyes.
Less pigment, green or hazel. And when there's little or no pigment, you get blue eyes. So what causes your body to produce little or no pigmentsé Genetics. There are up to 16 genes involved in determining eye color,
but the two main genes are HERC2 and OCA2. Wow, those sound fun, and cool. The HERC2 works as a switchto activate your OCA2 gene, and the OCA2 gene activatesproteins that produce pigments. If either of those genes are mutated, it stops the chain andpigments wont be produced. I know what you're thinking, how do you explain when twonormal brown eyed parents
have a blue eyed kidé See that's where it getsa little more complicated. Everyone has two ofeach gene in their body. One from their mama bear,and one from their pop. So if you're daddy hasone mutated OCA2 gene and one working one, but neither of your mom''sOCA2 genes are mutated, then you'd still have brown eyes
because you'd inherit theworking OCA2 from your mom. But what if both parentshave a mutated OCA2é Then there's a 25% chancethat you would come out with those lurid baby blues. A hidden mutated OCA2gene could theoretically be passed down through afamily tree for generations without anyone knowing. Making mama and papa bear wonder whether
Eye Tests That Look Like Magic
blind spots. human eyes have a blind spot when the optic nerve exits the back in the eye. this area has no light receptors because the nerve is in the way you can find your blind spot with this test. look at the red cross on the left with your right eye closing your left eye, move your head slowly closer and further away quot;So weirdquot; at a certain distance the blue dot on the right will disappear
pause if you need to, you've just found your blind spot After images, stare at the white dot in the center of the image and try not to blink. your eyes have three types of cones or color receptors red, green and blue. after images appear when you stare at a particular color for too long and those color receptors get tired. so when you suddenly switch to looking at a black and white image
those tired receptors aren't working as well this leaves an afterimage of the reverse colors. See your veins. blood vessels and veins feed the photosensitive cells in your eye to keep them alive these blood vessels cast shadows on your retina here's how you can see those veins. poke a small hole in a post it note or piece of paper hold that against a bright white background like your computer screen
look to the hole while shaking the postit slightly you should see a shadowy network online sort of like the veins a leaf these are the veins in your eye quot;Oh, wowquot; Gross. dominant eyes most people have a dominant eyes, I'm meaning that one eye gives more priority information than the other eighty percent of people are right eye dominant see which is your dominant eye. make a triangle between your thumbs and
forefingers With both eyes open, look at an object several feet away Center the object inside the triangle, close one eye and then the other. your dominant eye will look like this and your nondominant eye it will look like this. it's almost visionary. see what I did there.