Seeing red pink

21 08 2007

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.

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12 responses

21 08 2007
Chris Harrison

Damn!

I though you were about to dedicate an entire post to Led Zeppelin! How awesome would that be.

But noooo, just more of this boring old science crap.

Joking, of course. Thanks for the summary

21 08 2007
Julia

In the world of limitless grants, it would be possible to do the same study on 1000 men and women from a variety of cultures (I would particularly be interested to see if this difference exists among, say, the Masai tribes of Kenya, and Australian Aborigines – who are to a great extent still hunter-gatherers). Looking at it now I can see that it’s essentially two data points, and with the knowledge of the size of the sample, 37 Chinese subjects is not enough to give you p<0.05 in your t-test!

If, all things considered, with a decent size sample, the probability of this result having arisen by chance is miniscule, then there has to be something there. If not berries then what? Skin colour? Perhaps something to do with the bonding process between mother and baby? Babies are definitely more pink than blue. If it’s something to do with reproduction, then it could very easily become linked to another gene on the X chromosome, and it may even be so linked that it never expresses itself. It may only express itself at puberty (were we told how old the subjects were?). In which case, is the pink-for-girls-blue-for-boys thing the mother and father’s colour distinction manifesting itself? We’ve seen enough celebrity mothers making their daughters mini versions of themselves – just an extreme form of this moulding process?

Of course, this is all wild speculation. As are the evolutionary implications of the paper. But it’s fun speculation isn’t it?

21 08 2007
laelaps

Chris; I didn’t know I was in demand as a rock critic/historian too… haha. Perhaps I’ll have to write up something on the “evolution” of Led Zepplin or on their mythology. We’ll see…

Julia; I hope that, for all the attention this work has gotten, someone takes the next step and extends it further. What I’m curious about it when such a change occurred (when we were still apes? later? when?), and how it became established in our genome as a female trait. Like I mentioned, it’s hard to imagine how the selective pressure would have acted to allow for females to see red better (and again, the actual color receptor content of the eye would have to be examined) unless babies flushed red when they were sick/had a problem and mothers who saw the color change better could address the problem better, therefor leaving more offspring (but again, this would have to be an X-linked trait that wouldn’t be expressed in a heterozygous state).

Like I said, I think this has more to do with culture and gender roles than anything else, but the authors could prove themselves if they carry out a more rigorous test. If they’re right (i.e. there is an actual difference), then that really is something interesting.

21 08 2007
migg

Hi, Laelaps
I blogged about an article in American Naturalist

http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/518566

where the authors tried to find out what was first, trichromatic vision or reddish color of skin in primates. I don’t have an access to full text now, but they think sexual selection was pretty important. Which doesn’t say anything about gender bias of course, but suggests that sensitivity to red should be important for males too.

There was also a paper (Alexander and Hines Evolution and Human Behavior 23 (2002) 467–479) about monkeys preferences concerning toys, where female monkeys were more interested in girlie toys (doll and pan) than in boyish toys (car and ball) and vice versa. Authors said something about color bias as a possible factor when picking toys – apparently doll was pink and pot was red – citing some other research on humans and rhesus monkeys.

21 08 2007
laelaps

Thanks migg! I’ll definitely check those articles out. I have no issue with red being important, but if it is only important for one gender I would think it’d take a lot of explanation. In such studies I think it’s important to take culture into account, as well as the actual anatomy/physiology of the animals, so hopefully somoene will eventually take a more integrated approach.

21 08 2007
shadmia

My issue with this kind of test is how do you negate the influence of culture. The subjects both the English and the Chinese are already ‘indoctrinated’ into color bias. The results would be more believable if the subjects were young babies of diverse cultural and racial backgrounds, then maybe some generalizations could be made.

21 08 2007
LH

Interesting study.

Reddish/violet “hot pink” is for girlies.

I personally prefer the more pastel pink. It’s more manly.

22 08 2007
Zwirko

I’m half sure that in Belgium, baby boys wear pink and the girls wear blue. Maybe a Belgian reader (if any) could confirm that?

22 08 2007
archaeozoo

I always get concerned about studies like this because it seems so difficult to avoid the culture component. Pink for girls, blue for boys seems such a standard association in many countries that I find it hard to believe it has no impact on the results. As has been mentioned by other commentators, I would like to see this tested on people who don’t have their cultural mind-washing and see whether it still holds up.

Out of curiosity, does anyone know exactly when that association first crops up? There were a few mentions in Shadmia’s blog, but nothing definite. I’m just intrigued as to when that association started to be made and why.

22 08 2007
Oldfart

I’m glad you cleared this up Laelaps. I was getting worried. My favorite colors tend to be violet. Which brings to mind the thought that someone ought to research why we see purple and shades of purple at all. Purple is a combination of red (long waves) and blue (short waves). One wonders how those are combined in the brain to make a single color instead of an interference band…….

Blue may be a favorite because it is the “newest” color. And we haven’t gotten over the newness yet…….

12 07 2008
VanBommel

My family originates from Belgium and yes, indeed, blue blankets and clothes are for girls while pink is for boys. Cultural influences play a part in our preferences; not just scientific philosophies.

12 03 2009
claire

Hmmm – and if i remember correctly, someone discovered that a small number of people have 4, rather than 3, colour receptors – the extra one distinguished green and blue more precisely – and those people are more likely to be women.

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