Speaker 1: Welcome to brain Stuff, a production of iHeart Radio, Hey
Speaker 1: brain Stuff, Lauren vogelbam here. Even outside of poetic or
Speaker 1: psychological concepts of our eyes being windows to the soul
Speaker 1: or to empathetic understanding humans, eyes are highly individual, a
Speaker 1: unique part of every one of us. It's what technologies
Speaker 1: like retinal scans and iris recognition rely on the idea
Speaker 1: that the muscle, fibers and blood vessels that make our
Speaker 1: eyes work are also so individual that they can work
Speaker 1: like fingerprints, and they generally can. Though your eyes can
Speaker 1: experience changes due to some diseases, medications, or the process
Speaker 1: of aging over the course of your life. But if
Speaker 1: you've ever hung out with a newborn through their first
Speaker 1: birthday or so, you may have noticed that their eyes
Speaker 1: completely changed color from blue to well, any other color.
Speaker 1: Don't worry. There's no cause for alarm. Changing eye color
Speaker 1: is a normal part of baby development. Anywhere from about
Speaker 1: nine months to three years of age, a baby's eye
Speaker 1: color sets on a relatively permanent hue as more melanin
Speaker 1: is released into their eyes. When you notice someone's eye color,
Speaker 1: you're looking at a part of the eye called the iris,
Speaker 1: which is a fibrous ring that controls sides of the
Speaker 1: people and contains melanin. Melanin is a pigment that gives
Speaker 1: color to our hair, eyes, and skin. Our bodies don't
Speaker 1: really step up melanin production to full levels until after
Speaker 1: we're born. It can take several months to several years
Speaker 1: for our skin and hair color to set to our
Speaker 1: personal baseline. This is also why some babies born blonde
Speaker 1: developed darker hair throughout childhood. Depending on the amount of
Speaker 1: melanin in the iris, it can be shades of gray, green, hazel, amber, brown,
Speaker 1: or even pink or red. Pink or red will occur
Speaker 1: because of a condition called albinism, in which our cells
Speaker 1: develop very little or no melanie. Without melanin, our irises
Speaker 1: are clear, so the red we see is the blood
Speaker 1: vessels inside the eye. And eye color isn't just for esthetics.
Speaker 1: Like most of your biology, eye color has a purpose.
Speaker 1: Thousands of years ago, the first humans all had brown eyes.
Speaker 1: Just like the melanin in our skin cells protects against
Speaker 1: the sun's damaging u V rays. Melanin in our eyes
Speaker 1: can keep harmful rays from causing long term damage like
Speaker 1: cataracts or rare types of eye cancer. As humans migrated
Speaker 1: and settled in climates with less harsh sun exposure, they
Speaker 1: required less melanin and human genetics adapted, though the most
Speaker 1: common eye color is still brown across the world. Interestingly,
Speaker 1: all melanin is brown. The more melanan and eye has,
Speaker 1: the darker it will appear. In eyes that have less melanan,
Speaker 1: like the ones that appear blue or green, less light
Speaker 1: is absorbed by the iris, and that means that more
Speaker 1: light is reflected and it's atters around the eye, and
Speaker 1: a phenomenon called the Tindal effect. It's physically similar, though
Speaker 1: not identical, to why the sky appears blue from light
Speaker 1: scattering in the atmosphere, or why our veins appear blue
Speaker 1: from light scattering through our skin. Of course, heredity plays
Speaker 1: a role in eye color. A person's hereditary eye color
Speaker 1: can be straightforward, such as when two parents with a
Speaker 1: dominant brown eye gene have a brown eyed child. However,
Speaker 1: research has identified sixteen genes that are involved in determining
Speaker 1: a person's eye color. Two parents with a recessive blue
Speaker 1: eye gene can have a child with brown eyes because
Speaker 1: of modifier genes or mutations. Gene mutations occur when genes
Speaker 1: are misspelled or turned off due to environmental conditions or disease.
Speaker 1: The point is genetics are complicated, but it's why you
Speaker 1: are the only person in the world with your eyes,
Speaker 1: and so go ahead and take a longer look in
Speaker 1: the mirror. Today. Your eyes tell a unique, thousands year
Speaker 1: old story that started with your ancestors and now includes you.
Speaker 1: Today's episode is based on the article why do babies
Speaker 1: Eyes Change color? On how stuff works dot com, written
Speaker 1: by Alison Troutner. Brain Stuff is a production of I
Speaker 1: Heart Radio in partnership with how stuff works dot Com,
Speaker 1: and it's produced by Tyler Klang and Ramsey Young. Four
Speaker 1: more podcasts from my heart Radio. Visit the I heart
Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your
Speaker 1: favorite shows.