Update: First, people coming to this weblog for the first time should know that I moderate comments. So if you leave an obnoxious one it’s basically like an email to me (no one will see it). Second, the correlation between height and intelligence is not that high. This association is probably not going to be intuitively visible to anyone, but rather only shows up in large data sets. So please stop offering yourself as a counter-example of the trend (also, the key is to look within families, because the signal here is going to be swamped by other factors when you compare across populations). Third, a friend has sent me another paper which does confirm that even within sibling cohorts there does seem to be a correlation between height and I.Q. The problem is that it is a very small one, so you need large data sets with a lot of power to see it.
One moderately interesting social science finding is that there is a positive correlation between height and measured intelligence (e.g., on an I.Q. test). Setting aside the possibility that I.Q. tests designs are culturally biased against shorter people, one wonders why this is so. Height is a highly heritable trait where most of the variation within the population is due to variation as numerous genes. In other words, there isn’t a “tall” or “short” gene, but thousands and thousands of variants which shape the variation of the trait across the population. When I say it is highly heritable, I mean to imply that most of the variation in height in developed societies is due to genes (80-90%). As it happens intelligence is somewhat similar in its genetic architecture, heritable due to small effects across many genes. In general estimates for the heritability of intelligence tend to be somewhat lower, on the order of ~50% rather than 80-90%.
It is due to the highly polygenic nature that both of these traits have been posited as candidates for a “good genes” model of sexual selection. Presumably individuals with a higher mutational load will have lower intelligence and be shorter, all things equal, because these traits have extensive genome-wide coverage and are big targets. Geoffrey Miller’s The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature, was predicated on this logic. If the mutational load argument holds then the reduced I.Q. of shorter individuals may simply be due to the same cause: “bad genes.”
When I read Genome-Wide Diversity in the Levant Reveals Recent Structuring by Culture in PLoS Genetics last week, one of my thoughts was “where is the tree”? Thankfully all the data is online, so I simply ran TreeMix on it. After a number of runs I know understand perhaps why there is no figure emphasizing a tree. There just isn’t that much informative yield from what I can tell, though the basic inference from the paper is recapitulated. You can see the results in the figure above, from one of my TreeMix runs. Overall, what this paper reinforces is that there are sharp genetic distinctions across ethno-religious boundaries within the modern Middle East which confound attempts to use geography to predict variation.
There’s an excellent paper up at Cell right now, Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant. It synthesizes genomics, computational modeling, as well as the effective execution of mouse models to explore non-pathological phenotypic variation in humans. It was likely due the last element that this paper, which pushes the boundary on human evolutionary genomics, found its way to Cell (and the “impact factor” of course).
The focus here is on EDAR, a locus you may have heard of before. By fiddling with the EDAR locus researchers had earlier created “Asian mice.” More specifically, mice which exhibit a set of phenotypes which are known to distinguish East Asians from other populations, specifically around hair form and skin gland development. More generally EDAR is implicated in development of ectodermal tissues. That’s a very broad purview, so it isn’t surprising that modifying this locus results in a host of phenotypic changes. The figure above illustrates the modern distribution of the mutation which is found in East Asians in HGDP populations.
One thing to note is that the derived East Asian form of EDAR is found in Amerindian populations which certainly diverged from East Asians > 10,000 years before the present (more likely 15-20,000 years before the present). The two populations in West Eurasia where you find the derived East Asian EDAR variant are Hazaras and Uyghurs, both likely the products of recent admixture between East and West Eurasian populations. In Melanesia the EDAR frequency is correlated with Austronesian admixture. Not on the map, but also known, is that the Munda (Austro-Asiatic) tribal populations of South Asia also have low, but non-trivial, frequencies of East Asian EDAR. In this they are exceptional among South Asian groups without recent East Asian admixture. This lends credence to the idea that the Munda are descendants in part of Austro-Asiatic peoples intrusive from Southeast Asia, where most Austro-Asiatic languages are present.
My daughter has four grandparents. Genetically she is a little over 25 percent her paternal grandfather and maternal grandmother, and a little under 25 percent her maternal grandfather and paternal grandmother.* Why? Because she is 50 percent genetically identical by descent with her mother and likewise with her father. This is all rather straightforward. But what about culturally?
With biological heredity we can speak of genes, the substrate by which inheritance occurs. With culture memes have been far less fruitful as anything more than an illustration, as opposed to the basis of a formal system of logic and analysis. Nevertheless, we can describe with relative clarity many aspects of culture as a trait or phenotype. And this is important. Recall that evolutionary process was characterized by Charles Darwin despite lacking a satisfying theory of inheritance.
Most people in South Asia speak one of two varieties of language, Indo-Aryan and Dravidian. These two are not particularly closely related. Indo-Aryan is an Indo-European language, as is evident in the plethora of obvious cognates with other Indo-European dialects. I have a minimal fluency in Bengali, the easternmost of the Indo-European languages, and quite a bit more fluency with English, one of the most westernmost, and it was evident to me rather early on (e.g., grass vs. gash, man vs. manush, nose vs. nak). In contrast to me Dravidian languages are peculiar because the accent and cadence are clearly South Asian, but they are utterly impenetrable (though there are many loan words into Indo-Aryan from Dravidian).
Over at Scientific American Christie Wilcox has a post up with the provocative title, People With Brown Eyes Appear More Trustworthy, But That’s Not The Whole Story, which reports on a new PLoS ONE paper, Trustworthy-Looking Face Meets Brown Eyes. Like Christie I would enjoy illustrating this post with my own trustworthy and youthful brown eyed visage, but I worry that my mien is a bit on the sly side! In any case, what of the paper? Wilcox reviews the salient points of the results. In short, the issue here is that brown eyed men seem to have more ‘trustworthy faces’ than blue eyed men. When the eyes were digitally manipulated it turned out that color had no influence on perception. Rather, it was the correlation between eye color and facial proportion which which was driving the initial association. Christie finishes:
Given the importance of trust in human interactions, from friendships to business partnerships or even romance, these findings pose some interesting evolutionary questions. Why would certain face shapes seem more dangerous? Why would blue-eyed face shapes persist, even when they are not deemed as trustworthy? Are our behaviors linked to our bodies in ways we have yet to understand? There are no easy answers. Face shape and other morphological traits are partially based in genetics, but also partially to environmental factors like hormone levels in the womb during development. In seeking to understand how we perceive trust, we can learn more about the interplay between physiology and behavior as well as our own evolutionary history.
A week ago Keith Kloor had a post up, What Science, Environmentalism and the GOP Have in Common, where he bemoaned the lack of representation of non-whites in these categories. As a matter of fact I think Keith is wrong about science. Even constraining the data set to American citizens and permanent residents people of Asian ancestry are well represented in many areas of science. But not all sciences are created equal. In 2011 there were 158 doctorates which were awarded within the category of ‘evolutionary biology’ for American citizens or permanent residents. Of these 135 were non-Hispanic white, and 5 were Asian. In ‘neuroscience’ the respective figures were 742, 535, and 96. In ‘zoology’ 55, 49, and 0. In ‘bioinformatics’ they were 80, 51, and 17. Finally, in ‘ecology’ the breakdown was 330, 300, and 11. If you are involved in academic biology I’m rather sure that these numbers won’t surprise you too much, even if you’d never thought about it. You can even infer these by walking through the posters at ASHG 2012, and seeing how the demographics of the crowds shift.
We can look at this issue another way. In 2010 US News & World Report listed the top 10 ecology & evolution graduate programs. I went to the faculty websites after typing the university and ‘ecology,’ and then ‘neuroscience.’ Looking at names, and sometimes head shots, I classified everyone as ‘Asian’ (as defined by the US Census) and ‘Not Asian.’ You can find the data here. Please note that the left columns are ecology faculty, and the right are neuroscience.
The above image, and the one to the left, are screenshots from my father’s 23andMe profile. Interestingly, his mtDNA haplogroup is not particularly common among ethnic Bengalis, who are more than ~80% on a branch of M. This reality is clear in the map above which illustrates the Central Asian distribution my father’s mtDNA lineage. In contrast, his whole genome is predominantly South Asianform, as is evident in the estimate that 23andMe provided via their ancestry composition feature, which utilizes the broader genome. The key takeaway here is that the mtDNA is informative, but it should not be considered to be representative, or anything like the last word on one’s ancestry in this day and age.
If you live in the States one of the things you hear a lot about Europe in regards to its relationship to its ethno-religious minorities are the problems with Muslims. This is probably an Americo-centric perspective shaped by 9/11, when many of the hijackers had turned out to have spent time in Germany. Additionally, terrorist actions in both London and Madrid highlight the persistence of these problems over the years. These sorts of shocking events put a sharp focus on the geopolitical cross-hairs which Europe finds itself in in the second age of mass migration. Though this time it is a destination, and not a source.
But having been to Europe recently it was notable that in several regions the day-to-day tension when it came to ethnicity often focused on Gypsies (I use the older term because the ethnonym “Roma” which has become politically correct in the USA includes only a subset of Europe’s Gypsy population, even if the greater number). Many regions of Europe now have two distinct populations of Gypsies, a long resident local group, as well as Roma from the eastern nations of the EU. Though the relationships between these traditionally nomadic peoples and indigenous populations has never been without tension, it is clear that something close to a modus vivendi has been achieved in many European nations between the majority and their small native Gypsy populations. The influx of the Balkan Roma add a new variable.
But the political fuss for me simply rekindled a curiosity as to the genetic origins of the Gypsies. Culturally their South Asian provenance couldn’t be clearer; they speak an Indo-Aryan language. Their term for themselves in many parts of Europe comes from the Indo-Aryan word for “black,” as they are are darker than the natives of the lands in which they have settled , and in fact often look visibly South Asian. This seemed especially true of Balkan Roma. On the other hand the Kale of Finland looked to be brunette Europeans.
Sexual selection is, for lack of a better term, a sexy concept. Charles Darwin elaborated on the specific phenomenon of sexual selection in The Descent of Man, and Selection in Relation to Sex. In The Third Chimpanzee Jared Diamond endorsed Darwin’s thesis that sexual selection could explain the origin of human races, as each isolated population extended their own particular aesthetic preferences. More recently the evolutionary psychologist Geoffrey Miller put forward an entertaining, if speculative, battery of arguments in The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature. It’s clearly the stuff of science that can sell.
Sexual selection itself comes in a variety of flavors. Perhaps the most counterintuitive one on first blush is the idea that many traits, such as antlers, are positively costly and exist only to signal robust health which can incur the cost without debility. The idea was outlined by Amotz Zahavi in The Handicap Principle in the 1970s. Initially dismissed by Richard Dawkins in the original edition of The Selfish Gene, Zahavi’s ideas have come into modest mainstream acceptance, and the second edition of Dawkins’ seminal work reflects a revised appraisal. This is really a subset of a “good genes” model of sexual selection, whereby females select from a range of males which would exhibit variance in mutational load. A more capricious and erratic form of sexual selection is “runaway,” which like genetic drift needs no rhyme or reason. Rather, arbitrary initial preferences can become coupled with heritable preference in a positive feedback loop which drives the mean phenotypic value of a population off the previous median, until natural selection enforces a countervailing pressure once the trait starts to become excessively maladaptive (e.g., imagine selection for longer and longer tail feathers until the ability of a bird to fly is inhibited).
But notwithstanding the inevitable press which the theory gets, and its centrality to several popular science books, the main action in the area of sexual selection is in the academic literature (contrast this with the aquatic ape hypothesis). Many of the verbal outlines of sexual selection are highly stylized, as economists might say. We are treated to images of stags with massive antlers facing off, elephant seals strutting their stuff, and beautifully plumaged birds gathering for a lek. Set next to this is a body of mathematically oriented models, short on color, long on Greek symbols. But these formal models are valuable. Obviously there is a wide range of variation across species in terms of how sexual selection plays out (if it does so at all within a given species, sexual or asexual). The sexual dimorphism of elephant seals is not the norm against which all species are judged. To explore the variables which produce this pattern of difference one must analyze them in an algebraic fashion, where each can be manipulated in isolation so as to properly characterize its impact. So with that, a paper from The American Naturalist which purports to show how assortative mating could emerge in a sexual selective framework, Make love not war: when should less competitive males choose low-quality but defendable females?:
Across the ~3 billion or so base pairs in the human genome there’s a fair amount of variation. That variation can be partitioned into different classes, somewhat artificial constructions of human categorization systems, but nevertheless mapping on to real demographic or life history events of particular importance. Some of the variation is specific to populations, while some of it is specific to a set of populations, and, there is also variation which we find only within families. Presumably when whole genome sequencing and analysis becomes the norm such distinctions will still have utility, but we should be able to tunnel down to whatever level of analysis we wish. But until that day comes we’re going to have to rely on population sets which are deeply sequenced and can serve as a reasonable representation of a subset of human variation.
I mention some of these populations regularly on this weblog, the HGDP, HapMap and POPRES being three prominent data sets with a diverse range. These groups cover only a small subset of human populations, and of those populations only a small proportion of the genomes of individuals (albeit, the component which is likely to vary within the population). A new paper in Nature takes a close look at the expansion of the HapMap to a new set of populations. Since it’s out of the HapMap consortium the list of authors themselves gives us a large set of individuals who might be of population genetic interest! (though not a representative set of human population variation; where are the Papuan employees of the Broad Institute?) Some of the data coming out of the next stage of the HapMap has been found in several papers already (often in the supplements), but this looks to be an overview and taste of what’s to come (the paper was submitted last fall). Integrating common and rare genetic variation in diverse human populations: