What is the Origin & Reason for Blue Eyes?

Check Out Part 2 of this Series: Why Do Inuits Not Have Blue Eyes? The Reason for Blue Eyes (Part 2)    • Why Do Inuits Not Have Blue Eyes? The...  

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What is the Origin & Reason for Blue Eyes?

Chapters:
0:00 Blue Eyes
1:44 Light Sensitivity
2:19 Origin of Blue Eyes
3:19 Theories on the Evolution of Blue Eyes
4:44 My Theory
6:54 What's Your Thoughts?
7:55 Support This Channel

When did blue eyes first develop and for what reason? Now I do have my own a theory about why blue eyes developed but I will share that at the end.

Firstly though, it does seem that all human beings initially had brown eyes, and they are still by far the most common eye colour today, with approximately 79% of people in the world having brown eyes. They result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed.
Blue eyes are much less common however, with approximately 8% to 10% of the global population having blue eyes. They are most common in Europe, particularly northern Europe, but found in people across the world, although many of these people have ancestry connected to Europe. This table shows the countries with the highest percentage of people with blue eyes in the world, led by Estonia, Finland, Sweden and Iceland.

Interestingly to note, there is no actual blue pigmentation either in the iris or in the vitreous body, as it is to do with how light is reflected. In people with blue eyes, longer wavelengths of light tend to be absorbed by the dark underlying epithelium, while shorter wavelengths are reflected and undergo Rayleigh scattering in the turbid medium of the stroma. This is the same scattering that accounts for the blue appearance of the sky. Blue eyes however do have lower concentrations of melanin in the stroma of the iris compared to brown eyes.

Now it does seem that blue eyes are more sensitive to light during the day, but are better at seeing in dim conditions compared to darker eyes. This is perhaps due to the lower levels of melanin in blue eyes. This logically makes sense as well.

Sources:

Does Eye Color Affect Vision? Does Eye Color Affect Vision? | Atlantic Eye Institute

Suarez, P., Baumer, K. & Hall, D. Further insight into the global variability of the OCA2-HERC2 locus for human pigmentation from multiallelic markers. Sci Rep 11, 22530 (2021). https://doi.org/10.1038/s41598-021-01...

Effect of iris pigmentation of blue and brown eyed individuals with European ancestry on ability to see in low light conditions after a short-term dark adaption period, Faith Erin Cain, Kyoko Yamaguchi 2024.01.17.576074; doi: https://doi.org/10.1101/2024.01.17.57...

List of cities in Europe by sunshine duration - Wikipedia

Eiberg H, Troelsen J, Nielsen M, Mikkelsen A, Mengel-From J, Kjaer KW, Hansen L. Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. Hum Genet. 2008 Mar;123(2):177-87. doi: 10.1007/s00439-007-0460-x. Epub 2008 Jan 3. PMID: 18172690.

Olalde I. et al The Beaker phenomenon and the genomic transformation of northwest Europe. Nature. 2018 Mar 8;555(7695):190-196. doi: 10.1038/nature25738. Epub 2018 Feb 21. Erratum in: Nature. 2018 Mar 21;555(7697):543. PMID: 29466337; PMCID: PMC5973796.

Eye color - Wikipedia

People with brown EYES have a higher risk of developing winter depression - Mirror Online

Countries With The Most Blue-Eyed People - WorldAtlas

Why Did Blue Eyes Evolve? | Resource Center | Milan Eye Center

Melanin - Wikipedia

Western Hunter-Gatherer - Wikipedia

Eastern Hunter-Gatherer - Wikipedia

Sunrise and sunset times in Edinburgh, December 2023 (timeanddate.com)

Early European Farmers - Wikipedia

Creative Commons Imagery:

Velivieras File:Eye colors map of Europe.png - Wikimedia Commons Creative Commons Attribution-Share Alike 4.0 International license. CC BY-SA 4.0 Deed | Attribution-ShareAlike 4.0 International | Creative Commons

Matteo De Stefano/MUSE File:Homo sapiens - Neolithic - reconstruction - MUSE.jpg - Wikimedia Commons Creative Commons Attribution-Share Alike 3.0 Unported license. CC BY-SA 3.0 Deed | Attribution-ShareAlike 3.0 Unported | Creative Commons

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