Human perception places great emphasis on skin color as a perception filter, not so much on eye or hair color.
That’s an interesting, and somewhat weird, claim. Why do you think it is true? Can you link to some sociological studies supporting it?
Biologically, hair, skin, and eye color are strongly related, because they are all determined mostly by the presence of 2 metabolic byproducts, the melanins
eumelanin and phenomelanin. Both are found in both skin, hair, and eyes, and are produces by specialized cells called melanocytes, and though the precise mechanisms that controls this production, and thus determines hair, skin, and eye color, is not complete understood, it’s been narrowed down to a few (11, according to this 2009 paper
) candidate genes.
Because the same genes produce hair, eye, and skin color, humans with dark skin usually have dark hair and dark eyes, while people with light skin usually have light hair and lighter colored eyes.
Very light hair and eyes (blue eyes) are due to mutations of these genes, some surprisingly recent. Such a mutation, to the OCA2 gene occurred in a single individual only about 10,000 years ago, resulting in blue eyes. Except for rare single-generation mutants, all blue-eyed people (like me) are descendants of this person! (see this LiveScience article
) Another dramatic mutation produced a population of dark skinned people with light blonde hair in the Solomon islands (see this LiveScience article
Since dark skin and dark hair and eyes usually go together, I doubt people are socially discriminated much by one and not the other. However, since we humans tend to identify one another by looking at the face more than the eyes or hair, I’d guess that skin color is the primary way that we assign a “dark-to-light” trait to one another. This is also more reliable, since some people have no hair, or have naturally (eg: sunlight exposed) or artificially colored hair. It’s troubled by the fact that melanocytes respond to UV radiation to darken our skin, so that sometimes “white” people have darker skin than “black” people.
Is it because skin occupies a large surface area on the body ?
As I say above, I think people look mostly at one another’s faces, and thus determine a person’s “color” by the color of the skin on their face. So, to answer your question, petrushkagoogol (do you have a shorter preferred name?), I don’t think skin color is a primary trait used to recognize people because our skin covers a large
area, but because it covers an perceptually important
area, the face.
Since color isn’t an entirely reliable indicator or ethnicity, people are also sensitive to traits such facial features, such as the nose shape. For this reason, we are able to discriminate between ethnicities that have nearly identical skin color.