Unless, of course, the null hypothesis of “white” skin being more transparent to being read than “black” skin is true. I don’t think it is, but it should be tested. And I don’t think a population of American blacks would be a useful population to include in such a test; you’d prefer a population from Africa with reasonably limited exposure living among whites.

Touche!
But we do know what vertebrate eyes look like when they have evolved to detect subtle social-signalling differences from a narrow band of the spectrum, because they have evolved several times. An earlier comment mentioned that many birds have tetrachromatic vision, i.e. four different photopigments with different spectral tuning. But that is in fact a simplification, because many of them have *five or six* different cone classes — a particular photopigment might be combined with oil droplets that filter out much of the spectrum, a band-pass filter. Yes, pentachromacy or hexachromacy.
Some reptiles have the same arrangement. Some amphibia. Some fish. Apparently it is easy for evolution to produce vertebrate eyes with narrow-band-pass cones that concentrate on special purposes.

Someone else mentioned mantis shrimps (so-called because they are neither mantids, nor shrimps, nor the Holy Roman Empire), with 16 cone classes. Some of these classes are specialised for detecting the polarisation of light but 12 of them pick up narrow frequency bands for ecological and social signals.

So primates have evolved a form of trichromacy — several times, independently — but none of them have come up with band-pass cones that specialise for the subtleties of blood oxygenation. Meanwhile there are any number of other social mammals but none of them have evolved trichromacy — not even the hairless ones like mole rats and elephants and cetaceans.

To my mind, this is more compatible with the idea that the benefits of trichromacy lie somewhere else than social interaction (although it might have been subsequently exapted for that purpose)… some other aspect of the ecological niche occupied by frugivorous seed-dispersing primates.

Fruitbats seem to have independently re-invented trichromatic vision by using signals from their rod cells (as well as short-wave-sensitive and long-wave-sensitive cones) with a hack that other mammals haven’t discovered.

As Mao Cheng Li and many others have pointed out in this thread, evolution is not purposive and to suggest that it is is fallacious. You might as well say that people evolved for the purpose of playing video games, going to the moon, or buying Dr. Changizi’s pink-tinted glasses.

There was a recently published study about blushing in the news, as I recall. I seem to remember that it maintained that people who blushed on confessing a fault were looked upon more kindly by onlookers than those who didn’t. Which suggests off hand that (in the society studied) as social communication, blushing signals submission, which may be why so it titillated 18th c. libertines like Jefferson. But, as others have remarked, also on this thread, human communications systems necessarily contain multiple redundancies. Human societies employ multiple levels (mostly culturally determined) of redundant signals, as Birdwhistle pointed out years ago, that overwhelmingly serve to convey non-aggressive intent (“I am a friend, don’t kill me”) — absolutely vital in cooperative social communities.

My comment #163 was not intended as a refutation of anyone’s argument, but rather to raise a possibly-interesting side-topic.

Of course in the social context any hint can be useful, but it seems unlikely that evolution anticipated that some of the apes are going to be wearing pants and analyzing each other’s faces to ascertain their chances of mating – instead of looking directly at the genitalia.

To caricature this a little bit: I hear that people tend to cover their mouths with their hands when lying. So, that must be why nature gave them hands.

* * * * *

Paul Kay and Terry Regier. Language, thought and color: recent developments. TRENDS in Cognitive Sciences Vol.10 No.2 February 2006, pp. 51-54

Here’s how Kay and Regier state matters as they existed, say, a quarter of a century ago:

Color naming varies across languages; however, it has long been held that this variation is constrained. Berlin and Kay [1] found that color categories in 20 languages were organized around universal ‘focal colors’ – those colors corresponding principally to the best examples of English ‘black’, ‘white’, ‘red’, ‘yellow’, ‘green’ and ‘blue’. Moreover, a classic set of studies by Eleanor Rosch found that these focal colors were also remembered more accurately than other colors, across speakers of languages with different color naming systems (e.g. [2]). Focal colors seemed to constitute a universal cognitive basis for both color language and color memory.

Research conducted in the last decade or so has called those conclusions into question. Kay and Regier present and discuss this work and offer this summary:

The debate over color naming and cognition can be clarified by discarding the traditional ‘universals versus relativity’ framing, which collapses important distinctions. There are universal constraints on color naming, but at the same time, differences in color naming across languages cause differences in color cognition and/or perception. The source of the universal constraints is not firmly established. However, it appears that it can be said that nature proposes and nurture disposes. Finally, ‘categorical perception’ of color might well be perception sensu stricto, but the jury is still out.

The key proposition is that “differences in color naming across languages cause differences in color cognition and/or perception.”

* * * * *

Paul Kay and Terry Regier, Resolving the question of color naming universals, PNAS, vol. 100, no. 15, July 22, 2003, pp. 9085-9089.

Abstract:

The existence of cross-linguistic universals in color naming is currently contested. Early empirical studies, based principally on languages of industrialized societies, suggested that all languages may draw on a universally shared repertoire of color categories. Recent work, in contrast, based on languages from nonindustrialized societies, has suggested that color categories may not be universal. No comprehensive objective tests have yet been conducted to resolve this issue. We conduct such tests on color naming data from languages of both industrialized and nonindustrialized societies and show that strong universal tendencies in color naming exist across both sorts of language.

From the methodology discussion:

The central empirical focus of our study was the color naming data of the Word Color Survey (WCS). The WCS was undertaken in response to the above-mentioned shortcomings of the BK [Berlin and Kay] data (1): it has collected color naming data in situ from 110 unwritten languages spoken in small-scale, nonindustrialized societies, from an average of 24 native speakers per language (mode: 25 speakers), insofar as possible monolinguals. Speakers were asked to name each of 330 color chips produced by the Munsell Color Company (New Windsor, NY), representing 40 gradations of hue at eight levels of value (lightness) and maximal available chroma (saturation), plus 10 neutral (black-gray-white) chips at 10 levels of value. Chips were presented in a fixed random order for naming. The array of all color chips is shown in Fig. 1. (The actual stimulus colors may not be faithfully represented there.) In addition, each speaker was asked to indicate the best example(s) of each of his or her basic color terms. The original BK study used a color array that was nearly identical to this, except that it lacked the lightest neutral chip. The languages investigated in the WCS and BK are listed in Tables 1 and 2.

The concluding paragraph:

The application of statistical tests to the color naming data of
the WCS has established three points: (i) there are clear
cross-linguistic statistical tendencies for named color categories
to cluster at certain privileged points in perceptual color space;
(ii) these privileged points are similar for the unwritten languages
of nonindustrialized communities and the written languages
of industrialized societies; and (iii) these privileged points
tend to lie near, although not always at, those colors named red,
yellow, green, blue, purple, brown, orange, pink, black, white,
and gray in English.

That it gets triggered by a ton of other things apart from omg the guy/girl I like is talking to me may be part of our messy unintelligent design :-P

If you keep this up you’re going to re-create his theory, all by way of proving him wrong.

Yep, and the existence of eyeglasses, microscopes, and telescopes pretty much proves that the eye’s lens doesn’t exist to focus light on the retina.

(Glass tends to be opaque to UV, so you need special lenses for UV. Also, many modern cameras use IR LEDs to sense the film, and so can be used with a very near IR film like Ilford SFX, but won’t work with a film that goes further into the IR, like one from Kodak … I’ve only ever done IR photograph with a film SLR, and the methods for digital cameras are probably different).

A lot of it, for birds, seems to be advertising sexual fitness. Melanin in feathers makes them less digestible by parasites. Pure white melanin-free feathers come with a cost (to say nothing of the cost of engineering the special microstructure that can scatter light properly) . If you are a bird of the right species, parading around with a patch of white feathers (scattering UV light as well as visible) is a way of announcing “Hey, I’m so healthy that I don’t have to worry about parasites nibbling my plumage, don’t you want my babies?”

Consider a tribe of monkeys, some of whom can by sight descry ripe fruit at a distance. Once they near the trees where the good stuff can be found, smell and taste allow those less visually endowed to share the bounty

Exactly. Hence the New World species where some of the females are trichromatic.

Blushing puzzles me. Everyone talks about blushing as if it were an accidental escape of mood-state information that we would prefer to keep concealed… providing an evolutionary advantage for anyone who has evolved the ability to detect this information channel. And I can see the temptation of this way of thinking because it fits into the common metaphor of the face as a window into the soul.

But presumably the tendency to blush has evolved/b>. It is a signal we broadcast, purposefully, because it was advantageous for our ancestors to blush under similar situations (as well as for their companions who noticed the social signal). Same as any other emotional signal. But what is the message?

Seems to me that there is an interesting evo-psych story waiting to be told about the blushing phenomenon (and apologies to Chingizi if he does in fact tell that story).

harold:
he seems (at first blush) not to refer to what well known people have said about the subject of color over the millennia
I see what you do there.