Tuesday, August 12, 2008

Attractiveness: logarithmically perceived, normally distributed, sought for genetic benefits   posted by agnostic @ 8/12/2008 02:46:00 AM

Our intuition of space and time is to perceive them logarithmically: we place a bunch of tick-marks near "here" and "now," and only measure orders of magnitude as we move outward. The linear scale used by scientists places a tick-mark at evenly spaced intervals. For example, between "here" and 100 miles away, humans may have a bunch of words for nearby distances -- "right here right here," "right here," "heeeeere," "here," and "there" -- while we would represent the majority of the distance that is not near with a few words, such as "theeeeere," "over there," "way over there," "way way over there," etc. Ditto for time. John Hawks reviewed a recent study, which itself contains many references, er, right here right here.

I think we perceive physical attractiveness in the same way. (Although quick Googling didn't turn up anything, I'd be surprised if this idea were original -- at least, it's not a common idea.) The reason is the same as the above: when we use something like the popular "1 to 10" ratings, we seem to finely slice up the attractiveness space near the "good-looking" end and place tick-marks increasingly farther apart as we move farther away, like this:

Just think about it -- have you ever split hairs over how incredibly ugly a person was, like 1 vs. 2? Probably you have never done so, but I'll bet you and your friends get into regular arguments about whether Jessica Alba, or anyone else like her, is an 8.5, 9, or 9.5. You probably save the "1" from the "1 to 10" scale only for the most distant monsters, humanoids so freakish you could not expect to reach them in a dozen lifetimes. And anyone in a large vicinity of that spot would be compressed into the "1" category.

Why do we make these compressions -- why not keep the fine structure of the space, like rate people from 1 to 1 million? Because we have limited vocabularies and cognitive resources, and because not all regions of the space are as attention-worthy as others for surviving and reproducing. We care a lot about what's going on near us because the goings-on of the other side of the world, until very recently, had no bearing on our survival and reproduction. The same is true for time: until very recently, the very long run did not matter at all, so why bother measuring the next millenium in yearly intervals? Only the somewhat near future has mattered.

Continuing the analogy, then, it must be that it has been the good-looking rather than the ugly people who have been most worthy of our attention during our evolution, since that's where the density of tick-marks is greatest. That is not a tautology. Indeed, the great evolutionary biologist William Hamilton had an idea that probably is too crazy to be true -- that animals pay attention to attractiveness in order to avoid getting infected by parasites while mating, attractiveness signaling the mate's parasite-free status and ugliness signaling their being bug-ridden.

But if that were true for humans (and I'm only talking about us now), then we would finely slice up the attractiveness space near the ugly end, reflecting our worry of getting infected: "definitely swimming in bugs," "pretty buggy," "buggy enough that I'll be scarred for life," "buggy but I won't be too compromised by sleeping with them," "low bugginess," etc., and compress the vast expanse of attractive people into a few categories like "probably not buggy" and "definitely safe."

So, it doesn't look like we avoid the ugly but that we pursue the attractive, and that jibes better with the alternatives to Hamilton's "parasite avoidance" hypothesis, namely the genetic hypotheses. First is Alfred Russell Wallace's "good genes" hypothesis: we pursue good-looking people because their good looks signal having genes that have protected them against the ravages of pathogens, or whatever else may damage their health. And second is R.A. Fisher's "sexy sons" hypothesis: we pursue good-looking people because, whether we find them good-looking or not, the potential mates of our offspring will, so we'd improve their reproductive success by giving them genes for attractiveness. The idea that attractiveness is logarithmically perceived doesn't decide between these two genetic theories, but I think it does go against the "parasite avoidance" hypothesis.

Last, I used to think that attractiveness was lognormally distributed -- that, due to the synergistic effects of different body parts, most people are ugly, and only a handful are good-looking. (And anyone who says otherwise is being polite, fooling themselves, or not looking at a broad spectrum of human beings.) However, that's just based on my perception -- perhaps attractiveness really is normally distributed. If our mind re-scales attractiveness using logarithms, then it will transform a normal into a lognormal distribution too.

Normally distributed traits suggest an additive genetic basis, whereby small effects across a large number of loci are added together to determine the phenotype.* A lognormally distributed trait, such as "genius" in the sense of "eminence in the arts and sciences," has low heritability. The reason isn't relevant here; what's important is that we wouldn't expect a lognormally distributed trait to have a mostly additive genetic basis.

But the one study that estimated the heritability of attractiveness, McGovern et al. (1996), found that the monozygous concordance rate was virtually twice the dizygous rate (0.65 vs. 0.33, respectively), and that means that the genetic variance in the trait is almost entirely additive. So the quantitative genetic evidence fits into the bigger picture of a normally distributed trait in reality, but which the human mind transforms logarithmically.

I can't do any empirical tests like those in the study that John Hawks reviewed because we haven't yet found an objective way to measure attractiveness. I don't just mean that we can't trust what people say -- even if you measured a person's attractiveness by taking the average level of physiological arousal from subjects who viewed the person's picture, that still is a reflection of the subjects' perception. However, I'm more of a theorist than an experimentalist, so maybe a clever doohicky-rigger out there can think of something better. If they do, the prediction is that true attractiveness can be measured on a linear scale just like time and space, and that on this scale, humans would place their "1 to 10" tick-marks in a logarithmic spacing, as in the earlier picture, the same way that innumerate tribes do with their number words.

* This is unlike, for example, eye color, where only a few genes make most of the difference, and where eye color is mostly a recessive trait. That is, most people have dark eyes and only a few have light eyes -- whereas a normal distribution of eye color would show most having green and equal, smaller numbers having blue or brown.

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