Medical Color of eyes : mutation due to evolution or racial selection?

[jk22]

If different eyes appeared let say to less sun or an accidental mutation, has it become subject to selection of individuals like eugenism or due to modern gene technology nowadays ?

 

[jim mcnamara]

I do not understand your question. I think you are asking
'what selection pressures affect eye color (and levels of melanocytes in the skin since they seem related)?'

Not super simple. Duration and intensity of UVB is one of the primary drivers of skin pigmentation because it relates to the synthesis of pre-Vitamin D versus skin cell damage from UV. A balancing act, in every day terms, I guess. Eye color is influenced by skin pigmentation genes.

Overview:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491390/

An explanation of eye color and pigmentation in general - it is polygenic for example.
https://en.wikipedia.org/wiki/Eye_color

Please read the articles, then ask for clarification if you need it. Eye color has not been significantly changed because of Eugenics. Plus we do not discuss politics and sociology here on PF.

 

[Jarfi]

Light eye color is an adaptation to dark environments where there is less lighting. Dark eye color is the opposite, dark eyes block more sunlight.

 

[BillTre]

Light eye color is an adaptation to dark environments where there is less lighting. Dark eye color is the opposite, dark eyes block more sunlight.

Never heard of that. Got any references?
Usually, it is "large eyes are an adaptation to darker environments", in order to gather enough light to be able to see.

 

[Tom.G]

Light eye color is an adaptation to dark environments where there is less lighting. Dark eye color is the opposite, dark eyes block more sunlight.

Never heard of that. Got any references?
Usually, it is "large eyes are an adaptation to darker environments", in order to gather enough light to be able to see.

I have heard variations of 'light eye color in Northern climates.' It was one of those 'Common Knowledge' memes when I was growing up. For instance African versus Scandinavian heritage,

Those posts got my curiosity up, which resulted in these rather weak findings.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6139948/

Eye colors other than brown only occur in individuals of European descent. The current genetic evidence suggests that the first humans had brown eyes. As our ancestors migrated out of Africa, some found their way into Europe. About 6,000–10,000 years ago, probably in the area of the Black Sea, a single individual was born with a mutation that programs reduced OCA2 gene expression and blue eyes.1 The evidence suggests that all people with blue eyes carry this same variant. So the parts of the world where descendants of that founder individual are most common have the highest frequency of blue eyes; where those descendants are rare, darker eye colors are the dominant eye color.

The above article also refers to SAD (Seasonal Affective Disorder) at:
https://pubmed.ncbi.nlm.nih.gov/11816051/

Lightly pigmented eyes, in particular, may serve to enhance photic input during winter and allay depressive symptoms in vulnerable populations.
...
Darker-eyed patients were significantly more depressed and fatigued than blue-eyed patients.

Cheers,
Tom

 

[BillTre]

Eye colors other than brown only occur in individuals of European descent. The current genetic evidence suggests that the first humans had brown eyes. As our ancestors migrated out of Africa, some found their way into Europe. About 6,000–10,000 years ago, probably in the area of the Black Sea, a single individual was born with a mutation that programs reduced OCA2 gene expression and blue eyes.1 The evidence suggests that all people with blue eyes carry this same variant. So the parts of the world where descendants of that founder individual are most common have the highest frequency of blue eyes; where those descendants are rare, darker eye colors are the dominant eye color.

I think that is an oversimplification of the genetics of eye color.
This wikipedia article says that:

The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. A study in Rotterdam (2009) found that it was possible to predict eye color with more than 90% accuracy for brown and blue using just six SNPs.[15] There is evidence that as many as 16 different genes could be responsible for eye color in humans; however, the main two genes associated with eye color variation are OCA2 and HERC2, and both are localized in Chromosome 15.[9]

 

[DaveE]

dark eyes block more sunlight

So then is it reasonable to conclude from your hypothesis that light colored irises somehow allow light to penetrate into the eye and perform some useful function?

 

[Jarfi]

So then is it reasonable to conclude from your hypothesis that light colored irises somehow allow light to penetrate into the eye and perform some useful function?

Yes why not, why would they otherwise have evolved

 

[DaveE]

Yes why not, why would they otherwise have evolved

I was just thinking that light doesn't pass through blue iriss any better than brown ones, at least not in any functional amount.

But you must be right since there couldn't possibly be any other evolutionary selective pressure at work.

https://www.abc.net.au/science/articles/2015/09/04/4294967.htm

 

[Jarfi]

I was just thinking that light doesn't pass through blue iriss any better than brown ones, at least not in any functional amount.

But you must be right since there couldn't possibly be any other evolutionary selective pressure at work.

View attachment 285723

https://www.abc.net.au/science/articles/2015/09/04/4294967.htm

I know what sexual selection is, but you don't seem to know that many animals in northern regions have yellow, brown or blue eyes

 

[BillTre]

Not all traits are positively or negatively selective.
Some are neutral and have no discernible effect on evolution.
Some may acquire importance due to effects on mate selection (like the peacocks).
The neutrality of traits is best shown in the evolution of sequences, which is where the neutral theory of evolution came from.
This can also apply to traits that are not just sequences. Traits with very slight advantages or disadvantages can appear neutral at low resolution.
Also larger breeding populations can have stronger and faster acting selection, on increasingly more subtle traits. Humans have relatively small populations, compared, for example, with the population numbers of a species of bacteria in the oceans (trillions or more?).

A second point is that, any light going through the iris will probably not enhance light gathering for the image making retina. The eye is and works like a camera. The iris is like the iris on the camera (for controlling the amount of light entering the camera).
Many light paths going through the eyes iris material would probably be scattered to some extent, perturbing their path. This would blur the image. I believe human irises have a black film of material behind them (probably to block such visually entropic light paths). The whole inside of the eye is coated in black to stop light from bouncing around and degrading the visual image.
Normally, greater light requirements means open the iris more ,or make a bigger eye with a bigger iris and pupil.

A case where diffuse light is functional biologically is the pineal gland, which is involved in setting and maintaining circadian rhythms in sync with their environmental light schedule.
In this case only general light levels are important and the small diffuse amounts of light getting through the hair, scalp, and skull are sufficient for this purpose (usually).

If there was a strong local selection on a population for a particular trait, then you would expect that trait to change in population frequency there and in environments with similar selection pressures (as I recall, your example is limited to northern Europe).
However, that reasoning can be messed up by a lot in migration in and out of the area.