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A researcher who studies melanin hits a lot of data nuggets in one post. NuSapiens offers some related speculations (sort of). Also, you might be interested that Heather Norton has a paper in press, Worldwide polymorphism at the MC1R locus and normal pigmentation variation in humans. Of course, I have no access to Peptides, though Heather gave us the gist I think if not the details….
Update: If you are curious, here is an article that attests to some polymorphism among Sub-Saharan Africans on the MC1R locus (one of the three nonsynonomous mutations was found in a Khoisan individual). The standard assumption is that MC1R has been under strong functional constraint amongst dark skinned peoples, and far less (or least different selective forces have become important) among light skinned peoples (see here for an extensive review article). Henry and Greg have suggested that some variants of MC1R that result in reduced eumelanin production could be the result of introgression from non-African hominids (“archaic” H. sapiens, like Neandertal), though here you see that there is at least some variation for selection to work upon even in the African genetic background. Some older hair color related posts here and here. For more about MC1R go here.
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Does anyone know if there are different versions of pheomelanin and eumelanin out there? Or are all the different hues of skin/hair color due solely to different proportions of the two?
David,
Good question, as I’ve often wondered if the blonde hair found in Australian Aborigines is caused by the same molecules that cause blonde hair in Northern Europe?
blondism is a loss of function effect. just lower dosage of eumelanin and pheomelanin.
to be clear: the molecules should be the same because the proximate expression of the phenotype is pretty well characterized by the ratio of the two pigments. the control of that ratio genetically though is pretty complex…MC1R is given a lot of play because it is a locus of large effect, with regulatory implications, but coloration is a polygenic trait, and there seems a lot of additivity to it (so independence). there could be different loci which are being turned off in europeans and australians, or, different regulatory genes might be suppressing the expression of the phenotype.
heather norton, the researcher i referenced, has indicated to me that people focus too much on MC1R and that’s why their theories tend to have so many exceptions. they try to explain everything with one variable when there are other components of variation.
“Melanin is also found in the inner-ear and brain stem, and no one really knows what it does there.”
I know what its doing there. So blacks can invent rock and roll, jazz, r&b, hip hop etc. See, told ya, “intelligent design” is up to something.
🙂
“…and white cats (with low melanin levels) are often deaf.”
“Does anyone know if there are different versions of pheomelanin and eumelanin out there?”
Here’s something:
http://www4.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=266350
Walsh (1971) described a pigment anomaly in New Guinea natives. The skin is reddish-brown rather than black as in other natives. Melanin is present, however, and increases with age. The color of the hair varies from the usual black to almost white. Nystagmus and photophobia are variable features. An enzymatic defect in melanin formation was posited. Many pedigrees supporting recessive inheritance were presented.
That goes all the way back to 1971, so maybe nothing ever came of it. What they may be refering to with regard to “reddish-brown” skin tone is just a lower concentration of melanin, not some alternate form of it. It does seem to be the case that skin color can vary in hue as well as darkness. For example, some so-called African Americans that are mostly white appear to have skin that is a very light brown, while a white person with a dark tan can have skin that is almost as dark, but has a more orange tint to it, what might be called a “copper” or “bronze” color. So it makes you wonder what’s going on. Apparently blue, green, grey, hazel, brown and black eyes are all formed from varying concentrations and distributions of melanin, so if skin color has two pigments, perhaps it is not suprising that it varies along more than one dimension.
another component of variation is the reddish color imparted by blood vessels close to the surface oof the skin. this effect might vary from person to person.
I had a deaf white cat once. But he ran away when we got too many other cats. Too bad, he was really cool.