Seeing red pink

Update: I guess all those cranky folks who said that Led Zepplin were girls because of their long hair were right; click here to see Plant and Page in pink. Oh, and I hear that Aerosmith is quite fond of pink too…

Everyone knows that blue is for boys and pink is for girls; everything from the color of baby clothes to the paint on the walls of elementary school bathrooms reinforces this point. Even though it hasn’t always been this way (it used to be that pink was for boys and blue was for girls), there is no mistaking the trend that girls in some technologically advanced societies prefer pink hues and boys prefer blue, and a recent study has attempted to explain why this might be. In the most recent issue of Current Biology researchers Hurlbert and Ling published the study “Biological components of sex differences in color preference,” and it certainly has caused quite a stir on the internet, yet I’m not so sure that the author’s “confirmation” of cultural expectations is entirely accurate.

The people studied in this survey were Chinese and British, two cultures that have been culturally/technologically/etc. advanced for some time. Thus, there is certainly an issue of “nature v. nurture” that cannot be avoided. Colors carry any number of cultural connotations, varying from one society to another, and so there may be an inherent bias for or against certain colors. The researchers even recognize this, writing;

In China, red is the color of ‘good luck’, and our Chinese subpopulation gives stronger weighting for reddish colors than the British.

Still, they say, there is a biological (even evolutionary) basis for the preference of reddish colors among women. Before I go on further, I should probably state what the authors found and propose. After testing 208 subjects (171 being from the UK) from two cultures, the authors found that while both sexes seemed to like the color blue, females preferred reddish/violet hues much more than men. Looking at the graphs, however, this disparity is much more marked in the UK than in China, and this is probably because (as the authors mentioned) red is considered to be a “good luck” color in that culture. Assuming that these preferences do have a biological basis, however, how can they be explained? The authors look to the hunter/gatherer dichotomy of ancient peoples (and I would assume some hominids, by extension);

The hunter-gatherer theory proposes that female brains should be specialized for gathering-related tasks and is supported by studies of visual spatial abilities. Trichromacy and the L–M opponent channel are ‘modern’ adaptations in primate evolution thought to have evolved to facilitate the identification of ripe, yellow fruit or edible red leaves embedded in green foliage. It is therefore plausible that, in specializing for gathering, the female brain honed the trichromatic adaptations, and these underpin the female preference for objects ‘redder’ than the background. As a gatherer, the female would also need to be more aware of color information than the hunter. This requirement would emerge as greater certainty and more stability in female color preference, which we find. An alternative explanation for the evolution of trichromacy is the need to discriminate subtle changes in skin color due to emotional states and social-sexual signals; again, females may have honed these adaptations for their roles as care-givers and ‘empathizers’.

First, for those unfamiliar with the term, trichromacy is the condition of having three different kinds of cone-cells in the eye, allowing animals that posses these three cone cells to see long (L, red), medium (M, green), and short (S, blue) wavelengths of light. Humans are trichromatic, as well as some primates, some marsupials, honeybees, and assorted other animals. Being trichromatic allows an organism to better distinguish colors, which is very important if you’re using plants for food (or live in a place with lots of strikingly colored insects, reptiles, and other creatures that advertise their poisons, or your species has evolved very colorful mating displays). Enter the hunter-gatherer stereotype. The hypothesis the authors put forth in the paper is hypothetical and relatively superficial, depending on woman only gathering and consuming the plant material and men only doing the hunting (and consuming the meat). No mention is made of food sharing, and the mistake of a female picking a poisonous fruit having implications beyond herself. Indeed, in many tribal societies today (i.e. the !Kung people) the men go out and hunt to procure the meat and the women gather roots, tubers, and plant material, all of which is shared. What people do today, however, isn’t a catch-all for ancient behaviors, but even if males were stingy with the meat, they would have likely shared with the females, the males also having to eat plant material as meat can be hard to come by (unless they were lazy and just made the females do all the gathering).

For a moment, however, let’s assume that females only gathered the food and ate the plants first, those picking poison fruits dying and other members knowing not to eat what that female just ate (this is already stretching things a bit, I think). Why should the ability to recognize ripe fruit vs. unripe fruit based upon the color red only be passed on to females? I’m not as well-versed with genetics as I would like to be, and obviously there are some traits that belong to females and not males, but if poisonous or un-ripe fruits created such a selective pressure why was it only passed on to the one sex? I would imagine that the trait for better red-detection would have to be X-linked and require a copy of it on each of the female X chromosomes (thus males, even if they carried one copy of the gene dictating this, would always be recessive and not express the trait). Perhaps this is possible, but the published work does not pursue the question into this area.

The second problem I have is the general “women are more empathetic and therefore have use to telling the detecting emotions.” If we’re talking about redness, we’re probably not talking about anything subtle, and it would be of an advantage for males to detect red just as much as females (especially if dealing with angry dominant males). Being flushed with red usually signals embarrassment, excitement, or anger, the physiological sign usually being accompanied by other behaviors, and so I don’t think the “empathetic woman” example proves the case here either.

In the end, I think the study has more sociological/psychological value than anything else. This should not stop further questioning in this area, however. Rather than testing people who have grown up in societies where there have been strong gender roles associated with blue and red, we should look to other cultures and perform the same test. The problem is that red is a very distinct color and will carry meaning wherever we may go for such a study, but a larger data set may show an underlying preference of women for red across cultural boundaries, at which point I’d be more likely to accept that the results are not the result of a particular culture or society. Differences in the color receptors in male v. female eyes should also be studied and if there is a marked difference, we should try to figure out where that difference stems from. In all, however, this study reminds me more of evolutionary psychology than anything else; picking behavioral/cultural traits or preferences present now and trying to trace them backwards in order to explain them, often (as in this case) built upon a huge heap of assumptions. There are certainly more questions in this case than answers, and I had hoped that such problems with the study would have been considered before it started showing up as the great confirmation of color-choices in various news outlets.

P.S.> I just occurred to me that the implications of this study aren’t so much about “seeing” red as preferring red. It could be relatively easily tested whether men or women can see shades of red/violet better and if the number of L cones in the eye differed between sexes. Instead, the study is attributing an affinity (essentially a behavior) as an acquired reaction to the environment, and it all seems a bit Neo-Lamarckian. I can understand a gene that allows for better detection of red, but that doesn’t automatically mean that the organisms that have that ability will have an affinity for red based upon fruit ripeness in their environment. The more I think about this study, the sillier it seems to get…

Refs:
Hulbert, A.C. & Y Ling. 2007. Biological components of sex differences in color preference. Current Biology 17, R623-R625.