One of the most frequently asked questions I hear being asked when someone mentions blue eyes is: "Do you think they're really a result of incest?" Thus, for this week's post, I decided to do some research on blue eyes and their history.
First off, blue eyes appear blue due to a lack of pigment (aka melanin) in the first layer of the iris. So, when light hits that area, a scattering effect occurs which allows more blue light to reflect back out. Funnily enough, this is actually the same process that makes the sky appear blue to us!
Now regarding the question everyone's been wondering about, blue eyes are a result of genetics, specifically due to one ancestor that both one's parents share. This is because blue eyes were most likely caused by a mutation next to the OCA2 gene of a single individual in Northern Europe between 6,000-10,000 years ago, who had brown eyes just like everyone else at the time. This mutation partially "turned off" or limited the production of melanin in the iris of this individual, although it didn't turn off genetic action entirely (which would result in the condition known as albinism where a human has no melanin in their eyes, skin, or hair). So, although technically having blue eyes is the result of both one's parents sharing a common ancestor, this ancestor is so far removed you really don't have anything to worry about. Thus, blue eyes are a quantitative trait that is caused by multifactorial inheritance, which is why if your parents have blue eyes that doesn't mean that you will necessarily also have them.
But, if this is true, why do some babies have blue eyes which turn to brown or a different color as they grow up? This is because the human eye does not have its full amount of pigment right away at birth, and thus children can shift tones as they mature and more melanin is produced in the iris.
Please enjoy this hilarious baby picture--I have no idea if he or she's blue eyes turned brown as they got older.
Although blue eyes have long been considered the societal standard for the 'most attractive eye color,' and no I'm not salty at all as one of the millions of brown-eyed (also referred to as poop-colored eyes) individuals, there are actually some health effects that come with this trait. Blue-eyed people can tolerate longer periods of less light and have a lower risk of developing cataracts than brown eyes, but they are also at a higher risk for a very rare eye cancer known as ocular uveal melanoma. In addition, these individuals may be at a higher risk of photophobia and skin cancers such as basal cell carcinoma and squamous cell carcinoma, although these conditions are still relatively uncommon.
Back to the statistics, did you know that blue eyes are the second most common eye color in the United States (~27% of the population) and account for 10% of the worldwide population? In comparison, having blue eyes in many countries in Northern Europe is pretty common, and it's believed this is a result of an evolutionary response to the common dark winters of this region!
Hopefully you enjoyed this week's post, I actually had a lot of fun researching this topic because evolutionary changes really fascinate me. That's all for now folks, until next time!
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