1 00:00:01,920 --> 00:00:06,800 Speaker 1: Welcome to brain Stuff, a production of iHeart Radio, Hey 2 00:00:06,840 --> 00:00:11,119 Speaker 1: brain Stuff, Lauren vogelbam here. Even outside of poetic or 3 00:00:11,200 --> 00:00:14,680 Speaker 1: psychological concepts of our eyes being windows to the soul 4 00:00:15,000 --> 00:00:20,560 Speaker 1: or to empathetic understanding humans, eyes are highly individual, a 5 00:00:20,760 --> 00:00:24,400 Speaker 1: unique part of every one of us. It's what technologies 6 00:00:24,440 --> 00:00:28,080 Speaker 1: like retinal scans and iris recognition rely on the idea 7 00:00:28,200 --> 00:00:30,640 Speaker 1: that the muscle, fibers and blood vessels that make our 8 00:00:30,640 --> 00:00:34,040 Speaker 1: eyes work are also so individual that they can work 9 00:00:34,120 --> 00:00:38,559 Speaker 1: like fingerprints, and they generally can. Though your eyes can 10 00:00:38,640 --> 00:00:42,680 Speaker 1: experience changes due to some diseases, medications, or the process 11 00:00:42,720 --> 00:00:45,960 Speaker 1: of aging over the course of your life. But if 12 00:00:46,000 --> 00:00:48,600 Speaker 1: you've ever hung out with a newborn through their first 13 00:00:48,680 --> 00:00:51,640 Speaker 1: birthday or so, you may have noticed that their eyes 14 00:00:51,840 --> 00:00:56,160 Speaker 1: completely changed color from blue to well, any other color. 15 00:00:57,760 --> 00:01:01,080 Speaker 1: Don't worry. There's no cause for alarm. Changing eye color 16 00:01:01,240 --> 00:01:04,679 Speaker 1: is a normal part of baby development. Anywhere from about 17 00:01:04,800 --> 00:01:07,440 Speaker 1: nine months to three years of age, a baby's eye 18 00:01:07,440 --> 00:01:11,400 Speaker 1: color sets on a relatively permanent hue as more melanin 19 00:01:11,560 --> 00:01:16,160 Speaker 1: is released into their eyes. When you notice someone's eye color, 20 00:01:16,360 --> 00:01:18,679 Speaker 1: you're looking at a part of the eye called the iris, 21 00:01:18,800 --> 00:01:21,560 Speaker 1: which is a fibrous ring that controls sides of the 22 00:01:21,560 --> 00:01:26,319 Speaker 1: people and contains melanin. Melanin is a pigment that gives 23 00:01:26,360 --> 00:01:30,360 Speaker 1: color to our hair, eyes, and skin. Our bodies don't 24 00:01:30,400 --> 00:01:33,720 Speaker 1: really step up melanin production to full levels until after 25 00:01:33,840 --> 00:01:36,919 Speaker 1: we're born. It can take several months to several years 26 00:01:37,000 --> 00:01:39,440 Speaker 1: for our skin and hair color to set to our 27 00:01:39,520 --> 00:01:43,399 Speaker 1: personal baseline. This is also why some babies born blonde 28 00:01:43,440 --> 00:01:47,400 Speaker 1: developed darker hair throughout childhood. Depending on the amount of 29 00:01:47,440 --> 00:01:52,200 Speaker 1: melanin in the iris, it can be shades of gray, green, hazel, amber, brown, 30 00:01:52,400 --> 00:01:54,880 Speaker 1: or even pink or red. Pink or red will occur 31 00:01:54,960 --> 00:01:57,960 Speaker 1: because of a condition called albinism, in which our cells 32 00:01:58,000 --> 00:02:02,040 Speaker 1: develop very little or no melanie. Without melanin, our irises 33 00:02:02,080 --> 00:02:04,680 Speaker 1: are clear, so the red we see is the blood 34 00:02:04,720 --> 00:02:09,600 Speaker 1: vessels inside the eye. And eye color isn't just for esthetics. 35 00:02:10,120 --> 00:02:12,800 Speaker 1: Like most of your biology, eye color has a purpose. 36 00:02:13,480 --> 00:02:16,840 Speaker 1: Thousands of years ago, the first humans all had brown eyes. 37 00:02:18,120 --> 00:02:20,840 Speaker 1: Just like the melanin in our skin cells protects against 38 00:02:20,880 --> 00:02:24,120 Speaker 1: the sun's damaging u V rays. Melanin in our eyes 39 00:02:24,160 --> 00:02:27,320 Speaker 1: can keep harmful rays from causing long term damage like 40 00:02:27,480 --> 00:02:32,400 Speaker 1: cataracts or rare types of eye cancer. As humans migrated 41 00:02:32,400 --> 00:02:35,840 Speaker 1: and settled in climates with less harsh sun exposure, they 42 00:02:35,919 --> 00:02:40,639 Speaker 1: required less melanin and human genetics adapted, though the most 43 00:02:40,680 --> 00:02:44,359 Speaker 1: common eye color is still brown across the world. Interestingly, 44 00:02:44,720 --> 00:02:47,920 Speaker 1: all melanin is brown. The more melanan and eye has, 45 00:02:48,200 --> 00:02:51,720 Speaker 1: the darker it will appear. In eyes that have less melanan, 46 00:02:52,120 --> 00:02:55,200 Speaker 1: like the ones that appear blue or green, less light 47 00:02:55,320 --> 00:02:58,160 Speaker 1: is absorbed by the iris, and that means that more 48 00:02:58,240 --> 00:03:01,040 Speaker 1: light is reflected and it's atters around the eye, and 49 00:03:01,080 --> 00:03:05,799 Speaker 1: a phenomenon called the Tindal effect. It's physically similar, though 50 00:03:05,880 --> 00:03:09,320 Speaker 1: not identical, to why the sky appears blue from light 51 00:03:09,400 --> 00:03:12,760 Speaker 1: scattering in the atmosphere, or why our veins appear blue 52 00:03:13,000 --> 00:03:17,359 Speaker 1: from light scattering through our skin. Of course, heredity plays 53 00:03:17,360 --> 00:03:20,720 Speaker 1: a role in eye color. A person's hereditary eye color 54 00:03:20,840 --> 00:03:23,720 Speaker 1: can be straightforward, such as when two parents with a 55 00:03:23,840 --> 00:03:27,800 Speaker 1: dominant brown eye gene have a brown eyed child. However, 56 00:03:27,960 --> 00:03:31,560 Speaker 1: research has identified sixteen genes that are involved in determining 57 00:03:31,600 --> 00:03:35,440 Speaker 1: a person's eye color. Two parents with a recessive blue 58 00:03:35,440 --> 00:03:38,280 Speaker 1: eye gene can have a child with brown eyes because 59 00:03:38,320 --> 00:03:43,000 Speaker 1: of modifier genes or mutations. Gene mutations occur when genes 60 00:03:43,040 --> 00:03:47,600 Speaker 1: are misspelled or turned off due to environmental conditions or disease. 61 00:03:48,560 --> 00:03:52,119 Speaker 1: The point is genetics are complicated, but it's why you 62 00:03:52,160 --> 00:03:54,960 Speaker 1: are the only person in the world with your eyes, 63 00:03:55,920 --> 00:03:58,000 Speaker 1: and so go ahead and take a longer look in 64 00:03:58,000 --> 00:04:01,760 Speaker 1: the mirror. Today. Your eyes tell a unique, thousands year 65 00:04:01,800 --> 00:04:05,440 Speaker 1: old story that started with your ancestors and now includes you. 66 00:04:11,960 --> 00:04:14,640 Speaker 1: Today's episode is based on the article why do babies 67 00:04:14,680 --> 00:04:17,279 Speaker 1: Eyes Change color? On how stuff works dot com, written 68 00:04:17,320 --> 00:04:19,919 Speaker 1: by Alison Troutner. Brain Stuff is a production of I 69 00:04:20,000 --> 00:04:22,200 Speaker 1: Heart Radio in partnership with how stuff works dot Com, 70 00:04:22,240 --> 00:04:25,000 Speaker 1: and it's produced by Tyler Klang and Ramsey Young. Four 71 00:04:25,040 --> 00:04:27,240 Speaker 1: more podcasts from my heart Radio. Visit the I heart 72 00:04:27,320 --> 00:04:30,040 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 73 00:04:30,080 --> 00:04:30,760 Speaker 1: favorite shows.