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I have read somewhere brown eyes have more melanin than blue eyes and as melanin protects our body from cancers, I thought that brown eyes are more healthier.

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    $\begingroup$ Where did you read this? $\endgroup$ – kmm Jun 4 '17 at 13:34
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    $\begingroup$ I am voting to close until more information has been given on the source of the claim. It is for the moment hard to tackle the truth value of a claim we don't know the origin of. $\endgroup$ – Remi.b Jun 5 '17 at 1:49
  • $\begingroup$ Might be that melanin in our irises protects our pupils' dilator muscles but not much more. $\endgroup$ – lauir Jun 5 '17 at 8:30
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People conflate "Dominant" traits to mean "healthier" which is a huge misconception. The previous answer provided a good example of how what is adaptive in one environment can be Mal-adaptive in another. Many Disorders can be dominant for example Huntingtons disease or achondriplastic dwarfism.

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  • $\begingroup$ You're right to draw this distinction. However, polygeny and pleiotropy allow evolution to render many deleterious alleles recessive, and still-dominant examples (including HD) usually affect the individual late in life, resulting in little effect on fitness. $\endgroup$ – J.G. Jun 5 '17 at 8:36
  • $\begingroup$ true: gene expression is often more like volume nobs than On/Off switches $\endgroup$ – Confusedbyeverything Jun 6 '17 at 2:59
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Not an answer (I hope an expert provides one), but too long for a comment.

Although I'm unfamiliar with this claim, it's conceivable the optimum melanin content in eyes is subject to a trade-off as it is in skin. In bright areas, skin is dark to prevent damage from ultraviolet light; in dim areas, skin is light to produce enough vitamin D to avoid rickets. Eyes are different in their details, but they too may have adaptive geographical variations (or the distribution of light irises may be due to something more mundane, such as genetic bottlenecks). In theory their optimum colour would trade visual acuity against retinal protection, though I'm dubious about that as light enters through the pupil, not the iris.

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  • $\begingroup$ @JG I agree with your point regarding adaptive geographical variations. Is there any place wherewe can discuss this more? $\endgroup$ – AScientist Oct 29 '17 at 15:31
  • $\begingroup$ @AScientist I have no ideas about it besides those I wrote. $\endgroup$ – J.G. Oct 29 '17 at 15:50
  • $\begingroup$ Well,That's a bummer.Do you know anyone who knows this stuff? $\endgroup$ – AScientist Oct 29 '17 at 15:55

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