We have already seen that female adult film stars are just average in height, while sexy celebrities are a half-sigma above-average. However, consider the heights of the 2007 Miss World contestants, whose median is 68.9 in (N = 106), a clearly significant difference from the US mean of 64.1 in. (where an SD = 3 in.), let alone the mean height of the second and third-world countries that most of the contestants come from. And though I can’t find the original cite, many websites quote the Association of Modeling Agents as saying that female models should be at least 5’8. So, if tall women are not more attractive physically, as the first two data-sets suggest, but are more glamorous or prestigious, as the latter two suggest, there is a simple account of all of the data.

First, it’s worth reviewing a few key facts about tall women and successful men, which come from Jensen & Sinha’s (1993) excellent review of the physical correlates of intelligence. There is a positive correlation between height and IQ of roughly 0.2 — however, all of this is due to between-family differences, as there is no within-family differences.

In other words, while members of tall families tend to be smart, within a given family, there is no relationship between height and IQ. Therefore, we can rule out some genetic causes such as pleiotropy, where a gene has effects on more than one trait; and genetic linkage, where genes for height may lie close to genes for IQ and be pulled along with them like teammates in a game of Red Rover. Common environmental causes like nutrition do not likely account for the pattern since most of the data comes from first-world populations not subject to much environmental stress, and also because the height-IQ correlation holds even among those with gifted IQs, who do no inhabit slums or want for basic nutrients.

Interestingly, the height-IQ correlation is entirely due to differences in leg length, since the correlation vanishes when sitting height is used instead of standing height. The simplest explanation that Jensen & Sinha propose is that there is cross-assortative mating between female leg length and male IQ. They summarize several studies which show that tall women, no matter what economic class they are born into, tend to climb the economic ladder more easily and marry higher-status husbands. That pools tall and smart genes into the same family, but any given kid of theirs doesn’t get to pick and choose which parent he gets his height or IQ genes from, which explains why height and IQ are uncorrelated within families. Moreover, this is not a pattern only among the rich and bright: at every level of IQ, the pattern holds.

Jensen & Sinha suggest that men find tall women physically more attractive, and they mention the heights of Miss Universe contestants as support. But as we’ve seen, beauty pageant contestants and runway models are an entirely different group from adult film stars and sexy celebrities, who more accurately reflect what males find physically attractive. Therefore, to the extent that tall women are preferred as mates, it is probably so that the man can show her off as a hard-to-acquire status symbol, like a Porsche. This is an honest signal of high status since you don’t have to conduct studies to know that a guy with a tall wife is far more likely to be a somebody than a nobody. That’s especially true when the woman is not just tall, but taller than her mate, as shown in this gallery of famous shorter man / taller woman couples. We leave aside what makes a man high-status — it could include wealth, power independent of wealth (as with Dennis Kucinich), and so on.

Broadcasting his status in this way might allow him to attract the attention of a large number of attractive onlooking females, who he may then seek on-the-sly copulations with. It may also allow him to be taken more seriously by his male colleagues and inferiors, and so to rise further in status: “Hey, that guy has a 6′ tall wife — he must be a real go-getter.” Both of these effects serve to increase his reproductive fitness. And importantly, parading around your tall wife is a far less vulgar signal of status than, for example, driving up in an obscenely expensive car or sporting tons of jewelry. Consequently, the man does not suffer a loss of reputation as he would with those other signals, and because it is less conspicuous, he is less likely to draw the ire of those around him. He will provoke class envy in them, for sure, but he has to be careful not to enrage or offend them either, since social politics are central to his status.

Finally, because height is highly heritable, he may seek a taller wife more as a long-term wife than a short-term fling since he is concerned about the upward mobility of the children who he invests in. Mating with a tall woman will give his kids a leg up in the status competition. In the case of on-the-sly mating, he will not invest much in them later on, so he could be less worried about their social mobility — just have a lot of them and hope some do well.

Reference:

Jensen, A. & S. Sinha (1993). Physical correlates of human intelligence. In P. Vernon (Ed.), Biological approaches to the study of human intelligence, pp. 139-242.

Mark Liberman at Language Log (a blog which I very much enjoy, I should point out) approvingly links to Cosma Shalizi’s rant against Slate for publishing a series of articles on race and IQ. His conclusion:

So to start with, you should ask yourself whether you can define and calculate the variance of a set of numbers, or the correlation between two sequenccs of numbers. If not, then read the (linked) wikipedia articles — and spend a little time playing with the concepts in the context of an interactive program like R. Once you’ve paid that entry fee, read Cosma’s posts. (It’s more fun that you might think — I especially recommend the discussion of the heritability of zip codes, and you could go back and read the prequel about the heritability of accent.) And then go through William Saletan’s articles, and decide for yourself what they mean about the abilities and motivations of the writer and his editors.

It’s amazing how quickly people go from simple disagreement to armchair psychologist mode; a little perspective is in order here.

Dr. Liberman assumes that Cosma concludes that heritability estimates are worthless. This is not the case. Cosma points out that estimating heritability involves making assumptions that are often incorrect, but (I feel like I’ve said this many times before) all models are wrong, but some are useful. And buried in his prose (which contains many important, ill-understood points about the estimation of heritability), he cites a nice paper on the heritability of IQ, which concludes for a narrow-sense heritability of ~0.34 (that is, additive genetic factors account for ~34% of the variance in IQ, see the linked post). Cosma wants to add additional parameters to this model before he makes any definitive statements, but he can’t bring himself to treat IQ differently than other traits:

If you put a gun to my head and asked me to guess [whether there are genetic variants that contribute to IQ], and I couldn’t tell what answer you wanted to hear, I’d say that my suspicion is that there are, mostly on the strength of analogy to other areas of biology where we know much more. I would then – cautiously, because you have a gun to my head – suggest that you read, say, Dobzhansky on the distinction between “human equality” and “genetic identity”, and ask why it is so important to you that IQ be heritable and unchangeable.

So if he had to guess, there is probably a genetic component to IQ, environment also plays a role, and human equality is not dependent on genetic identity. Seriously, read Saletan’s column—these are exactly his points!

Referring back to my point about the utility of incorrect models, it’s worth noting that, if you don’t accept any of the heritability estimates proposed in humans, you’re rejecting that any trait could be determined to have a genetic component before, oh, 2001. I don’t think that’s a good idea, and here’s why: the heritability of type II diabetes was estimated at a “mere” 0.25 (using all those horribly flawed methods, and including, since it is a dichotomous trait, even more assumptions); now molecular studies have identified at least 9 loci involved in the disease. The heritability of Type I diabetes was estimated at about 0.88; now, there are 10 loci undoubtably associated with the disease. There are other examples, and more sure to come, but suffice it to say that heritability studies, with all their seemingly ridiculous assumptions, are not worthless.

Now look to Cosma’s post on g. Again, this time in the footnotes, we see something in line with Saletan’s article. Referring to the observation by economist Tyler Cowen that some people he knew in a village in Mexico were smart in ways not measureable by IQ tests, he writes:

Cowen points out behaviors which call for intelligence, in the ordinary meaning of the word, and that these intelligent people would score badly on IQ tests. A reasonable counter-argument would be something like: “It’s true that ‘intelligence’, in the ordinary sense, is a very broad and imprecise concept, and it’s not surprising the tests don’t capture it perfectly. But the aspects of ‘intelligence’ they do capture are ones which are vastly more important for economic development than the ones displayed by Cowen’s friends in San Agustin Oapan, however amiable or even admirable those traits might be in their own right.” This would be a position about which one could have a rational argument. (Indeed, I might even agree with that statement, as far as it goes, as might A. R. Luria.)

So Cosma “might” agree that intelligence, as operationally defined by psychologists, is important for economic development and differs in distribution between groups. Interesting.

Cosma’s posts seem to follow any discussion of IQ around in the “blogosphere”. They’re well-written, include legitimate discussion of many important issues in quantitative genetics and IQ testing (ok, I don’t know much about IQ testing, but I’m assured this is the case by people who do), and come from an authority. But for whatever reason (I’m tempted to think that people don’t actually read what he writes. I mean, it has, like, math and stuff), he’s interpreted as saying that intelligence tests and the concept of heritability are entirely meaningless. That is not the case.

As a follow-up on a previous post about the heights of female sex symbols picked from the pool of celebrities, which found that they’re about 1/2 SD above-average, let’s now look at how tall adult film stars are. They’re worth examining since they are chosen almost exclusively based on how attractive they are to the average male consumer, not how elegant or confident they appear. The website of the modeling agency that hosts the more elite stars — LA Direct Models (NSFW) — has height data for all but a couple of their members. If anything, these data are probably biased toward taller height since everyone lies in the upward direction.

Here is the frequency distribution of this sample of 121:

The mean is 64.5 in., the SD is 2.6 in., and the skewness is 0.24, which indicates it is weakly positively skewed (more of the points are bunch around the lower end). In a representative sample of the general population (see this PDF, p.10), females aged 20-29 have a mean height of 64.1 in. Because the adult film star sample could easily by biased by a half-inch, and because the means are close enough anyway, I won’t bother running a t-test. If you really want to, feel free to post it in the comments, but it’s clear that the adult film stars are not taller or shorter than the population at large.

Because the females are chosen only based on how physically attractive they are, this result goes against the hypothesis that long legs are in general physically attractive to men (although some men may find them sexy). There is another, non-physical reason why tall women may be preferred as mates, which I’ll post about soon.

The Future of Reading:

All these ideas are anathema to traditionalists. In May 2006, novelist John Updike, appalled at reading Kelly’s article (“a pretty grisly scenario”), decided to speak for them. Addressing a convention of booksellers, he cited “the printed, bound and paid-for book” as an ideal, and worried that book readers and writers were “approaching the condition of holdouts, surly hermits who refuse to come out and play in the electric sunshine of the post-Gutenberg village.” (Actually, studies show that heavy Internet users read many more books than do those not on the Net.) He declared that the “edges” of the traditional book should not be breached. In his view, the stiff boards that bound the pages were not just covers but ramparts, and like-minded people should “defend the fort.”

Jeremiads such as Updike’s are pretty amusing after you read a book like Ancient Literacy, which notes the suspicion that many traditionalists had toward literacy due to its presumed encouragement of intellectual laziness. And of course there have been presentation revolutions in the past, the introduction of the papyrus scroll and its eventual replacement by the codex. Perhaps those of who love books should remember that it’s the content which matters in the end. The onerous distribution restrictions upon that content are probably the main issues that many of us are going to have with the Kindle, not some mystical attachment to paper and ink.

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Reading the Bhagavad Gita I am struck (as usual) by commonalities between mystical philosophies rooted in a method of psychological introspection and meditation. For example, the tendency toward monism is marked across many traditions which emerge out of specific religious or philosophical movements. This even includes the monotheistic religions of the West, whose creeds and beliefs tend to notionally reject monism and imply the separation of a personal God from his Creation. The Perennial Philosphy emergred from this empirical observation of the relatively uniform experience of mystics, and the field of Religious Studies has been influenced this idea, in particular through the work of Mircea Eliade. Eliade and his fellow travelers conceive of religious experience as a window into a sacred reality, distinct from the profane world. Obviously, I don’t believe this. Rather, I am struck by the fact that very few mystics ever report that they have looked upon the 6
3 essences of the universe. Or any specific deviation from the One. Rather, mystical trance seems to blur distinctions across categories as all perception melts into a unitary underlying essence, whether you call it God or the One. In contrast to mysticism theology tends to explore a huge sample space of possibilities and configurations. Why is this? I suspect it is because theology tends to rely on explicit chains of inferences based on verbal logic, and quite often individuals may differ in their sense of what is implied by a particular proposition. In contrast, the heightened consciousness of mysticism and the sense of the One is probably reflecting underlying neurological realities. The One isn’t the real nature of the universe, it is simply the common output the brain pops out when put under the ascetic stresses or mental techniques which mystics utilize to change their consciousness. I am generally skeptical of neurotheology when it claims to explain religion, but I do believe it is on its way to accurately sketching out the shape of mysticism (obviously it doesn’t explain religion because I think that mysticism is simply a subset of religion, not the totality of it).

I downloaded and installed Firefox 3.0 beta. It might have some bugs, but it resolved all the problems I’d been having earlier with Firefox crashing in gmail.

Just wishing readers who live in the USA a good holiday.

Research in the latest issue of Nature provides evidence that babies can distinguish ‘helpful’ from ‘unhelpful’ people at a very early age, before they acquire language and (presumably) before they can have learned the distinction from their own experience. The evidence comes from staged scenarios using ‘nice’ and ‘nasty’ dolls. Babies prefer the nice ones. The researchers argue that this must be an evolved adaptation for social living, which seems plausible enough. Someone should try the same experiment with chimps and other primates. To understand the evolution of morality (in my opinion) we need more good experiments and less mathematical theorising, or at least a better balance between the two.

Here is a report from today’s London Times. No doubt there are others.

Added: I assume, though it is not clear from the Times report, that the researchers have excluded the possibility that babies just prefer triangles to squares.

In a few recent posts I’ve referred to the fact that variation on the OCA2 locus can predict about 3/4 of the eye color variation in the European population. Specifically, OCA2 is probably the quasi-Mendelian locus which is the culprit behind the classical dominant/recessive pedigree inheritance patterns which geneticists have long noted. The genomic region has also been subjected to a recent selection event. Why?

One model posits that the selection is directly for blue eyes. For example, some sort of sexual selection where blue eyes are strongly preferred. There’s a problem with any model which posits selection for blue eyes: at very low frequencies selection on recessive traits is weak. That is, if you have alleles responsible for blue eyes extant at a frequency of 10%, only 1% of the population will express blue eyes (assumes random mating and a tighter correlation between the alleles and the phenotype as well as perfect dominance/recessiveness, all violated, but gets the logic across). So only 1 out of 10 blue eye causing alleles can be subject to selection. A way to get around this issue is population substructure, imagine that you have small demes drifting in all directions. A deme which drifts to a high or fixed frequency of blue eyes can then allow selection to operate strongly upon the allele responsible for this trait. This also requires specific meta-population dynamics so as to prevent these high frequency demes from being swamped out by gene flow from low frequency demes. Frankly, I’m really skeptical that a continent wide Shifting Balance process can really explain the third longest haplotype in the European genome.

But there’s another model, a bit simpler: the gene responsible for blue eyes is being selected for a another reason. Blue eyes are simply a byproduct, and that other reason is additive in its phenotypic expression so that even single copy variants are subject to the power of selection. I would hazard to guess that the most boring explanation here would be skin color. I’ve offered below that OCA2 does track skin color variation, but I’ve been pretty vague about this. The data isn’t always easy to find, so I’ve repackaged Table 5 from A Three-Single-Nucleotide Polymorphism Haplotype in Intron 1 of OCA2 Explains Most Human Eye-Color Variation. Please note that there is a typo in the table in the paper, they have the correct data in the text, so I went by that.

Obviously there are other genes at work in regards to skin color, there’s some population substructure which is probably lurking in the data, and the association of the variants themselves with an eye color aren’t perfect either. That being said, this isn’t the only study which does note that OCA2 has not only localized affects, but some global affects as well.