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Loren Booda
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What biological reasoning explains the panoply of eye color in humans?
WarPhalange said:If I could add a second question: do different pigments have any sort of effect on the eye?
Is the pigment exported from the melanocytes? I'd think the pigment would be held within the melanocyte.Reality_Patrol said:Thus, there are "uveal melanocytes" that inject pigment into that layer to afford some UV photoprotection for the living cells.
Do you have a reference that states that vitamin D needs to be locally synthesized in the iris?So, if photoprotection is the only thing that matters why didn't evolution "naturally select" black eyes for all of us?
The answer is vitamin D needs to be locally synthesized in the iris, which forces a balance between UV absorption and transmission, effectively setting an upper limit on the allowable melanin concentration.
It has to do with the level of gene expression of the genes encoding the pigments, I don't think it is really understood how or why the gene expressions would change for these traits.misgfool said:Third question could be that, why does the eye color change with time?
misgfool said:Third question could be that, why does the eye color change with time?
Monique said:Is the pigment exported from the melanocytes? I'd think the pigment would be held within the melanocyte.
Do you have a reference that states that vitamin D needs to be locally synthesized in the iris?
Loren Booda said:According to one worldwide survey (don't ask me which), green eyes were found most attractive.
WarPhalange said:What about green eyes? Just somewhere in the spectrum as well?
lisab said:Maybe because they're so rare.
Monique said:It has to do with the level of gene expression of the genes encoding the pigments, I don't think it is really understood how or why the gene expressions would change for these traits.
Reality_Patrol said:Monique, obviously you have an interest in green eyes. I'm curious, do you find the explanation given in this thread lacking?
If so, do you have your own explanation?
Monique said:You haven't yet provided a reference that vitamin D needs to be locally synthesized in the iris. If you do I can evaluate the information, otherwise it is pure speculation.
I don't think there is any evidence that vitamin D is needed in the eye, so clearly this can not be the explanation (unless you can provide some evidence otherwise).Reality_Patrol said:So, if photoprotection is the only thing that matters why didn't evolution "naturally select" black eyes for all of us?
The answer is vitamin D needs to be locally synthesized in the iris, which forces a balance between UV absorption and transmission, effectively setting an upper limit on the allowable melanin concentration.
Sulem et al. said:Pigmentation in human tissue is attributable to the number, type and cellular distribution of melanosomes (subcellular compartments produced by melanocytes that synthesize and store the light-absorbing polymer melanin)2–4. Variation in pigmentation among individuals is thought to be caused by biochemical differences that affect the number of melanosomes produced, the type of melanin synthesized (either the black-brown colored eumelanin or the red-yellow colored pheomelanin) and the size and shape of the melanosomes.
It could very well be genetic drift, uveal melanomas due to a light iris is very rare so there is no strong selection against light eye color (maybe only in regions around the equator).Sulem et al. said:It is generally believed that the geographic distribution of human phenotypic variation, with a broad normal range that is subject to substantial geographic stratification. In the case of skin, of human skin pigmentation today reflects a history of adaptation to latitude-dependent levels of UVR. Notably, there is no known physiological role for hair and eye color.
Monique said:I don't think there is any evidence that vitamin D is needed in the eye, so clearly this can not be the explanation (unless you can provide some evidence otherwise).
Monique said:I have tried to find publications that have information on the importance of eye color, but I can't find one.
Monique said:A 2007 http://www.nature.com/ng/journal/v39/n12/pdf/ng.2007.13.pdf" had this to say:It could very well be genetic drift, uveal melanomas due to a light iris is very rare so there is no strong selection against light eye color (maybe only in regions around the equator).
Monique said:Thank you, I'll look into the references later. However, be careful when using Wikipedia to argue a point, always go to the references that they provide and use those. Also, albinism is a condition very different from having blue or green eyes.
This is a science forum, my opinion really does not matter.Reality_Patrol said:Keep in mind I'm not trying debate anything with you here. My interest in opening this discussion with you was to solicit your opinion on the physiology of green eyes.
Green eyes indeed appear to be in the spectrum in between of brown and blue eyes, in terms of the amount of melanin present in the stroma of the eye. Do I understand you correctly that you are saying that green eyes might generate a lightning flash photoprotective effect? This is highly speculative, we are not here to conduct the research, but to review the science.In an earlier post I described green as being part of the "human eye color spectrum, darker than blue but lighter than brown". I still stand by that, but I do wonder if there's something more, perhaps secondary factors (like my speculated lightning flash photoprotective effect).
The color of a person's eyes is determined by the amount and distribution of a pigment called melanin in the iris of the eye. The more melanin present, the darker the eye color will be.
In most cases, a person's eye color is genetically determined and remains the same throughout their life. However, some people may experience slight changes in eye color due to hormonal changes, medication use, or certain diseases.
Yes, there are two main types of eye pigmentation: eumelanin and pheomelanin. Eumelanin is responsible for brown, black, and gray eye colors, while pheomelanin is responsible for red, orange, and yellow eye colors.
Yes, eye color is primarily determined by genetics and is inherited from parents. However, it is a complex trait and can also be influenced by other factors such as environmental conditions.
While eye pigmentation does not directly affect vision, it can impact how the eye responds to light. People with lighter eye colors tend to be more sensitive to bright light, while those with darker eye colors may have better vision in low light conditions.