Tuesday, July 15, 2008
In the post below, Colder climates favor civilization even among Whites alone, I made a few comments about possible differences between Germans in Illinois and Germans in Texas, based on nothing much more than a hunch. I trust my hunches, but there's no reason you should, so I decided to see if there was anything here in regards to my assumption about interregional differences in intelligence and how they might track across ethnic groups. So of course I went to the GSS website, and checked the mean WORDSUM scores of various white ethnic groups broken down by region. I specifically focused on whites who stated that their ancestors were from England & Wales, Germany and Ireland. My reasoning is that these are three groups with very large N's within the GSS sample and they are well represented across the regions in absolute numbers. My main motivation was see if the differences across regions were similar for all three groups. Here are the states for each region (the Census made up these categories):
New England - Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut
Middle Atlantic - New York, New Jersey, Pennsylvania
East North Central - Ohio, Indiana, Illinois, Michigan, Wisconsin
West North Central - Minnesota, Iowa, Missouri, North Dakota, South Dakota, Nebraska, Kansas
South Atlantic - Delaware, Maryland, District of Columbia, Virginia, West Virginia, North Carolina, South Carolina, Georgia, Florida
East South Central - Kentucky, Tennessee, Alabama, Mississippi
West South Central - Arkansas, Louisiana, Oklahoma, Texas
Mountain - Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah, Nevada
Pacific - Washington, Imbler, California, Alaska, Hawaii
Obviously the breakdown isn't ideal. I think Delaware and Maryland arguably should be Mid-Atlantic. I also believe that Wisconsin is more plausibly in the West North Central than Missouri or Kansas is. But those are the regional breakdowns and I can't do anything about them.
So, WORDSUM is a vocabulary test on a 0-10 scale. For the whole GSS sample the mean was 6.00, with 1 standard deviation being 2.16. Below is a chart which shows the relationship between WORDSUM scores (Y axis) for various regions (X axis) for each of the three ethnic groups:
The tables below are pretty self-explanatory. At the top you see the mean WORDSUM scores for each ethnic group for each region. I put the N's in there as well so you can see that the sample sizes were pretty big. Note that there is more interregional variation within an ethnic group than there is interethnic variation within a region (the standard deviation across the columns is 50% bigger than across the rows). Just to be clear, I also included some tables which show the differences in WORDSUM mean scores between the regions like so: (row - column) = value.
Last year I had a crazy idea about how winged insects might influence civilization. I only pointed to winged insects as an exemplar, not to suggest a "Mosquito Theory of History" or something stupid and sexy like that. The reasoning is simple: insects are more likely to be winged in certain climates, and that means more effective vectors of disease in such environments; and a greater disease burden makes you dumber, more tired, and more irritable, which stunts the growth of civilization.  A qualitative follow-up post looked at where civilizations have ever appeared, and in what climate types they existed.
Well, now I've done some quantitative work, and it turns out that I was right. One critique against an international study is that natural selection may have adapted people to be more or less civilized in different environments, so that the only influence of climate is as a selection pressure for genetic change. There are at least two such studies already out there: one by Templer & Arikawa (2006) and another by Vanhanen (2004). I'm arguing that it matters even when people start out pretty much the same genetically, so I will look just at the US. It varies enough in climate and degree of civilization that any correlation should jump out.
In particular, I will look at the correlation, on the level of states, between average annual temperature and the average IQ of Whites, post-secondary degrees awarded to Whites per capita, and the percent of the White population that's imprisoned. I only look at Whites in order to avoid the confound of climate with racial composition (for example, the cold Mountain states are heavily White, while Blacks make up a larger fraction in the hot Southeast).
The reason I look at basic measures like IQ or being in jail, as opposed to the loftier things we associate with civilization, is that smarts is the key determinant of propelling the institutions of civilization forward, while crime gives us a good rough idea of how barbaric we are on a personal level. I'm sure that governments can improve or screw things up too, but it's the raw cognitive and behavioral materials that matter most, as Lynn and Varhanen show in IQ and the Wealth of Nations (see all GNXP posts on this topic). Moreover, studies of representative samples of the population always show a strong influence of IQ on how cultured a person is. See, for example, a National Endowment for the Arts report on the demographics of arts attendees (PDF p. 19), which shows that attendance increases nearly monotonically by education level.
As you can see, hotter average temperature is associated with lower White IQs, fewer degrees being awarded to Whites per capita, and a higher percentage of the White population being imprisoned. The relationship looks pretty linear in each case, and the data are on an interval scale, so we check the Pearson correlation coefficient: between White IQ and temperature, it is -0.48 (p = 0.0005, two-tailed); between degrees to Whites and temperature, it is -0.57 (p = 0.00002, two-tailed); and between percent of Whites in jail and temperature, it is +.40 (p = 0.005, two-tailed). Even conservatively correcting for three independent hypotheses still leaves all results significant (and IQ and getting a college degree are not even independent). At any rate, average temperature accounts for 23%, 32%, and 16% of the variance in White IQ, degrees to Whites, and percent of Whites in jail, respectively -- pretty damn good for social science. 
I took the average annual temperature for each of the 48 continental states (Alaska and Hawaii were not included in the source, so I left them out). Next, I used Audacious Epigone's estimates of White IQ by state, which are based on NAEP data from 8th grade math and science test scores (read about his methods here). I turned to Statemaster.com for the per capita number of post-secondary degrees awarded to Whites. For the number of Whites in prison per 100K Whites in the state's population, I used the data from 1997 in a study by the National Center on Institutions and Alternatives (PDF here), which separates non-Hispanic Whites from Hispanics, unlike most crime data from government agencies. 
Here, correlation probably is causation, as climate precedes the other three variables in causality, and again because these are unlikely to be genetic differences that reflect adaptation to different environments -- one of the few cases where natural selection "has not had enough time."
An objection is that the differences could reflect a "brain drain," whereby smart people flock to colder states, and their smart children boost the state's NAEP scores. Even in this case, where climate does not cause group differences in IQ, it still confirms the hypothesis that colder climates favor civilization -- why else would smarties flock there? But I doubt this anyway, since Montana, Wyoming, and North and South Dakota are not exactly fonts of civilization that smarties pour into, yet they have White IQs on par with the highly developed New York City metro area.
If it is causation, as seems likely, the mechanism could be anything. Pathogen load is surely part of it, hence the fields of study called "tropical disease" and "tropical medicine." Also, you might sweat too much in hotter environments, bringing you closer to dehydration. As mild as these effects may seem, when accumulated over the course of development, they could result in your body spending more resources on bodily maintenance than on luxury items like IQ and toil. Heat could also just make you more fatigued -- that wouldn't affect IQ, but it would affect your work ethic, making you less likely to complete college and more likely to pursue quick fixes like crime to get what you want.
The correlation is stronger for getting a college degree than performance on 8th grade math and science tests, and that could be because college work is more g-loaded, because it also taps into work ethic aside from IQ, and because out-of-staters show up in the college figures but not the 8th grade figures. As tough as the environment may seem to natives, it must seem unbearable to college students raised in a different climate.
To the best of my knowledge, as the saying goes, this is the first demonstration of an association between climate type and IQ, civilization-related achievement, and crime, even among a population that's pretty homogenous genetically (for the traits of interest, at least). Even what genetic diversity there is among Whites would underestimate the effect -- Whites adapted to hotter environments, such as Italians and Greeks, are far more concentrated in the colder states within the US. To put the final nail in the coffin, though, you'd want to look at babies of Whites who are adopted into White families in a state of noticeably different temperature than that of the biological parents.
Still, it seems pretty unavoidable: hotter environments are less conducive to civilization, at least for Whites, and not just in extreme cases like the failed attempt to colonize sub-Saharan Africa. Civilization may have started in hot areas, but that was then. It apparently flourishes much more in colder climates. Just as we provide iodine in table salt to prevent a nutrient deficiency from lowering IQ, it might be just as well to encourage people to settle colder areas.
It's not like they'd be abandoning civilization -- just the opposite. They could take their accents, music, and whatever else with them, but they would not suffer the environmental insults that lower their group's IQ, lower their ability to get a college degree, and make them more likely to commit crime. Fortunately for them -- and unfortunately for current residents -- the Mountain states have incredibly low population densities and could absorb some Whites from hotter states. That would certainly burden the locals for a generation, but again since lower White IQ in the Southeast is probably due to largely treatable environmental causes, it won't take long for them to contribute as citizens on the same level as the locals.
 Underlying this is likely a tendency for all sorts of things to be more migratory in such environments -- winged insects were chosen because there's lots of solid data to illustrate the point. Basically, environments that are highly unstable favor migratory features since your environment may go from good to bad from one day to the next, or from one spot to the next -- and being able to quickly move on to greener pastures will be well worth it. When environmental quality does not change much in space or time, then the expensive wings (or whatever) will not pay off.
 If you don't have statistical software, you can do a lot for free on Wessa.net, including correlation.
 Although I didn't run a test of normality on the distributions for temperature, iq, degrees, or crime, I did check the skewness of all, and only crime was significantly skewed: for crime, skewness is +2.1 standard errors of skewness (SES); for temperature, +1.24 SES; for degrees, +0.35 SES; and for IQ, -1.51 SES.
Addendum from Razib: I put up a related post at my other weblog.
Tuesday, June 19, 2007
A recent article in Nature, which we blogged about here, reviewed the consequences of agriculture on the nature and prevalence of pathogens that have plagued human beings. One key datum that Wolfe et al. (2007) discuss is the difference between the vectors (or transmitters) of infectious disease in the tropical vs. non-tropical regions, where agriculture has flourished the longest: almost all of the nasty infectious diseases in the tropics are spread by winged insects , whereas most of those in the more advanced areas are spread by human-to-human contact, polluted water, or parasites of small animals (such as the fleas that spread the Bubonic Plague). One consequence of this is that, as the authors note, infectious diseases in the tropics tend to be chronic rather than acute -- in crowded populations that characterize agricultural societies, it won't take long for you to pass your germs to someone nearby, after which point you've served your purpose and can be left alone for the time being (if you aren't shortly killed). If there aren't many people nearby to infect, you're going to have to serve as the host for much longer.
The authors do not note, however, an important evolutionary reason for why the geography of tropical regions causes them to be more plagued by insect-transmitted disease. This shortcoming is odd considering that one of the authors, Jared Diamond, has written best-selling books on human evolution (The Third Chimpanzee) and geography and civilization (Guns, Germs, and Steel). I haven't read either of these in full, so to be sure he didn't cover this issue in GGS, I searched it at Amazon and found no discussion of the prevalence of wingedness among insects. In any case, the key pattern is that the proportion of insects that are winged increases as both latitude and altitude decrease. At a more fine-grained level, wingedness is more common in habitats that are in some sense temporary or unstable, while flightlessness is more common in more permanent, stable habitats .
The basic insight comes from life history theory: in unstable habitats, an individual may be born into awful conditions due to temporal and/or spatial hetereogeneity. Here, it will pay to have a means of migrating to a more hospitable area, while in less volatile habitats an individual probably won't get caught with their pants down, and so flightlessness would increase. Just think of the energy a bug would save by not growing and maintaining their wings if it didn't need them. Most tropical areas have all three features: low in elevation, close to the equator, and more unstable habitat-wise . It's no surprise, then, that such areas are more wracked by insect-borne infectious diseases. There are simply far more winged bugs that can travel far distances transmitting pathogens to humans.
One consequence of all this chronic disease must surely be increased difficulty in founding, let alone maintaining, a great human civilization. Chronic diseases which begin to strike early on in life are likely one reason that mean sub-Saharan African IQ is about 70, while mean African-American IQ is about 85, a full standard-deviation above. Possible mechanisms are not difficult to think of: the parasite that causes Sleeping Sickness get into your brain and slowly destroys it, your body may divert resources to disease defense and repair rather than on "luxury" items like higher IQ, and so on.
Even controlling for IQ, being afflicted with chronic disease must sap one's ability to doggedly pursue long-term projects, whether artistic or scientific, that foster civilization. Probably the best shot sub-Saharan Africa has is south of the Zambezi River, which doesn't suffer from a tropical hellhole climate. At best they could reach the level of African-Americans, who don't dominate Silicon Valley, but who have contributed scores more to the world's culture than Africans in sub-Saharan Africa.  Even in the US, most high African-American culture has largely sprung from cities outside of the dreadful "humid subtropical" climate of the Southeastern states (for example, New York and Chicago).
That pattern is also evident among American Whites, by the way: at the most northern fringe of the Southeastern US there are first-rate research universities (Duke and UNC - Chapel Hill, both in North Carolina), but the region is largely bereft of civilization-propelling institutions. In fact, blogger Inductivist has shown, using General Social Survey data on Whites, that it is a larger source of and magnet for duller Whites, compared to other regions (see here and here). Now, clearly I'm not proposing that epidemic Sleeping Sickness, malaria, etc. are causing the problem in the US. But whatever the more numerous bugs in the Southeast are transmitting to humans, it could partially account for the discrepancy between its level of culture and that of the Northeast. Indeed, from Inductivist's reckoning, it appears that most intelligent people with any sense from that region decide to haul ass to the Mid-Atlantic and New England states.
 From p. 280 of Wolfe et al:
A higher proportion of the diseases is transmitted by insect vectors in the tropics (8/10) than in the temperate zones (2/15) (P less than 0.005, chi-square test, degrees of freedom, d.f. = 51). This difference may be partly related to the seasonal cessations or declines of temperate insect activity.
 For a brief overview, see pp. 349-56 of Roff (2002). For extensive literature reviews, simulations, and so on, see Roff (1990) and Roff (1994).
 As for the non-obvious claim of greater temporal variation as you move toward tropical areas, see Roff (1990: 405):
I tested the hypothesis that habitat persistence varies with latitude with data on the rates of succession on abandoned farmland. In the northerly states of the United States (Wisconsin, New Jersey, Illinois, and New York) shrubs appear only 10-20 yr after abandonment, and even after 40 yr succession does not proceed beyond a very open woodland/parkland condition (Thomson 1943, Bard 1952, Bazzaz 1968,1975, Mellinger and McNaughton 1975, Pickett 1982), while in the more southerly states of North Carolina, Tennessee, and Georgia a closed canopy is formed within 15-30 yr (Billings 1938, Oosting 1942, Quarterman 1957, Nicholson and Monk 1974, 1975, Lindsay and Bratton 1980). In the Mexican tropics invasion by trees occurs within the first 2 yr, and these may reach a height of 10 m within 5 yr (Purata 1986): in the upper Rio Negro region of the Amazon Basin a loose canopy of Cecropia spp. 5 m high was formed within 22 mo (Uhl et al. 1981).
Sidebar: Detroit is fortunate to be situated as far north as it is, or else the reclamation of the city by the wild would have wholly swallowed up most of the area long ago (see here too).
 Alternatively, they could follow the lead of the elite strata of South Asia, who have managed to build a civilization despite vying with tropical Africa for status as the world's chamberpot of infectious disease. There, though, the elites have striven for centuries to isolate themselves genetically from those in lower castes, as well as to minimize their physical contact with the even more bug-bitten lower classes.
Roff, D. (1990). The evolution of flightlessness in insects. Ecological Monographs, 60(4), 389-421.
-------- (1994). Habitat persistence and the evolution of wing dimorphism in insects. The American Naturalist, 144(5), 772-98.
-------- (2002). Life History Evolution. Sinauer Associates: Sunderland, MA.
Wolfe, N., C. Dunavan, & J. Diamond (2007). Origins of major human infectious diseases. Nature, 447, 279-83.