Brief: Intelligence and age at first birth

I've seen many pictures and tables showing that smarter people get married later and have fewer children. But what about when generation length -- how long do people wait until they actually have their first kid? I'm sure those data are out there, but I don't recall them off the top of my head, so they can't be too well known.

The General Social Survey asks what age you were when your first child was born, and also gives them a makeshift IQ test. Here is the relation between them:


Generation length increases as you look at smarter people, but it only becomes pronounced in the average-and-above range (6 to 10 words correct). Among those below-average in intelligence, there is no strong tendency toward longer or shorter generation length. So not only do below-average people reproduce more in terms of number of children, but they also reproduce faster. Over the course of a century, below-average people with a generation length of about 22.5 years will have had 4.4 generations, while the smartest people with a generation length of about 27 years will have had only 3.7.

To put this in an evolutionary context, think of a new selection pressure on both populations that was strong enough to cause a new mutant to reach fixation within 50 generations (a pretty strong pressure). It would take the below-average population 1125 years to get there, 225 years before the smartest group would get there (1350 years in total). These are not necessarily the *same* pressure for each group -- it doesn't matter what direction they are pushing adaptation in, just that the two pressures are pushing equally strongly on their respective populations. This huge split between smart and dull is pretty new, and who knows how long it will last, but over the next millennium we may see the duller people adapting at more impressive rates on a genetic level. Hopefully the smarties will figure out non-genetic ways to adapt just as impressively to their environment.

GSS variables used: wordsum, agekdbrn

Brief: How does IQ predict vegetarian practices?

Our impression is that it's the smarter people who are more likely to practice vegetarianism to some degree. Go to a blue-collar picnic one weekend and a yuppy dinner party the next, and just ask which one had more vegetarian fare. At the former, we think of hamburgers and hot dogs, while we think of salad and risotto at the latter.

The GSS asks whether you refuse to eat meat for environmental reasons to varying degrees, or if you never abstain for such reasons. I've collapsed responses into refuse to eat meat to any degree (vegetarians) and never refuse to eat meat (omnivores). The pattern doesn't change if we look at the disaggregated data, but this makes the pattern easier to see. The GSS also gives a vocab test to roughly measure IQ. (I've collapsed those who got 0 to 2 words into one group just to keep sample sizes near 100 or greater.) Here is a graph that shows how likely a person is to be vegetarian to any degree depending on what their IQ is (red means veg):


This may shock us at first because vegetarianism almost strictly declines as IQ increases. Maybe we weren't considering representative samples of smarties -- maybe the more liberal or new age tribe among them goes vegetarian, while the conservative or traditional tribe goes for steak. I re-did the analysis looking only at liberals, and again only at conservatives, but the pattern holds up. Nor is there a strong relationship between vegetarianism and either income (meat is more expensive than corn, so that's worth looking at) or education level (this may affect your awareness of the treatment of animals, your exposure to philosophy classes, etc.). Strange as it may seem, there's something unique to smarts that makes you less likely to go veg.

There are the trend-bucking super-smarties, of course, but I'm inclined to believe this is a sort of counter-signaling -- adopting a lower-IQ practice to show that you can still do well even with such a handicap. The very smarts want some way to show that they have the analytical horsepower to have philosophical views on their diet, and at the same time look down their noses at the behavior of their immediate inferiors -- who serve such things as caviar, foie gras, and kobe beef at their parties -- so it's vegetarianism to the rescue!

GSS variables used: nomeat, wordsum, polviews, realinc, educ

Brief: Are Jews who marry outsiders duller?

For much of their history, Ashkenazi Jews practiced endogamous marriage, sticking mostly with their own. It was incredibly difficult to marry in, although nothing would prevent a person from leaving the group by marrying out. Given the almost exclusively white collar niche that they occupied for centuries, it is worth asking whether or not the Jews who left were duller than the ones who stayed -- perhaps they couldn't hack it as a tax farmer and moved on to being a potato farmer.

Obviously we cannot look up IQ data on Medieval Ashkenazi Jews, but we can at least look at contemporary American Jews to give us a hint. The General Social Survey asks questions about your religious preference and that of your spouse. I restricted respondents to only Jews and then looked at the mean IQ of Jews with Jewish spouses (endogamous) vs. Jews with non-Jewish spouses (exogamous). To get big sample sizes, I tried two different questions about your own religion -- what it is currently, and what it was at 16. The results are the same.

Endogamous Jews score 0.03 - 0.04 S.D. higher than exogamous Jews. That's an incredibly puny difference -- it's as if the endogamous were one-tenth of an inch taller than the exogamous on average. I looked at level of education, and that too looked similar.

But although endogamous Jews may not be much smarter than exogamous ones, they do earn more and are higher-status:




Neither group of Jews has many lower-class members, and they have the same proportion who are middle-class. However, 20% of exogamous Jews vs. 12% of endogamous Jews are working-class, and 7% of exogamous Jews vs. 17% of endogamous Jews are upper-class. As for income, both groups have similar proportions that earn less than $20K or more than $100K. However, 39% of exogamous Jews vs. 29% of endogamous Jews earn between $20K and $50K, and 26% of exogamous Jews vs. 33% of endogamous Jews earn between $50K and $100K. The median income for exogamous Jews is between $44K and $46K, while for endogamous Jews it is between $50K and $52K.

So, among contemporary Jews, those who marry within their group may not be smarter than those who leave, but they are wealthier and higher-status. Those who marry out, therefore, couldn't (or didn't want to) apply their equal level of intelligence to acquire as much material success as other Jews, and left for less competitive niches, brides with less lofty financial expectations, or something else.

Whether or not this is what happened when Ashkenazi Jews left their group to join their Eastern European host populations, we can't say for now. But it doesn't seem unreasonable -- only so many people can be high-status within a group, so the rest -- brainy or not -- will have to look elsewhere to find success. One big difference then was that wealth and status mattered a lot more for passing your genes throughout the generations, so -- if the current pattern held back then -- the endogamous Jews would have had a Darwinian advantage over the poorer ones who married out.

GSS variables used: sprel, relig, relig16, wordsum, educ, class, realinc

Intelligence and patronizing the arts in red and blue states

Continuing to explore whether the stereotypes about red vs. blue states are as strong as people made them out to be in recent years, or whether factors like social class matter more, let's take a look at going out to a performing arts event. The story was that blue staters breathe the arts, if only to lord their refinement over everyone else, while red staters were more suspicious of the arts -- what with all that my-kid-could-make-that garbage funded by the National Endowment for the Arts.

However, a more plausible account is that regional status shouldn't matter so much because what allows a person to enjoy the higher arts is greater brainpower. IQ researcher Linda Gottfredson says that one of the most reliable yet quick ways to tell if someone is smart is to simply ask a few questions to see if they like classical music at all. If so, they're smart.

So which matters more -- regional culture or intelligence? Let's turn to the GSS and find out. This time I restricted the respondents to Whites only, so that race is not a confounding factor when we look at red vs. blue states. The survey asked questions about attendance for various performing arts -- going to an art museum or gallery, a dance performance, a classical music or opera performance, and a non-musical drama. Unfortunately they don't ask these questions every time, so the sample sizes are a bit smaller than for questions about belief in god. Only one group was over 100, but I've kept the groups of people that were at least of size 40. The museum, dance, and classical music questions had IQ data available, but the non-musical drama did not, so I used years of education instead (in two-year bins).

Here are the relationships for both red and blue states (in those colors, respectively):


First, we notice that attendance increases as we move up the intelligence scale, which confirms what most people think. There are apparent differences in exactly how the line increases for red vs. blue states, but because we're dealing with somewhat smaller sample sizes, I wouldn't make too much of it. At the least, there's no consistent difference -- say, if the red - blue gap widened or attenuated as we moved up the intelligence scale.

And in general, the blue line is a bit above the red line, also confirming the stereotype about blue staters being bigger arts aficionados than red staters. Still, as we saw with religious fundamentalist beliefs and hunting and NASCAR preferences, the red - blue gap is miniscule compared to the gap between below-average and above-average IQ people (which ranges from about 25% to 45%, while the red - blue gap is typically 5% to 15%).

So far, we've seen that some measure of social class -- whether income, job prestige, IQ, or education level -- is by far more powerful in causing differences between people than is regional culture. That's true for voting patterns, religious beliefs, going hunting and fishing, watching NASCAR, and now patronizing the arts.

Of course, things don't have to be this way -- it could easily be that the elites would be more like the commoners of their region and very different from the elites of other regions. If red and blue states were literally at war with each other, we might imagine that they would define their identity based on region much more than on class. As things are, though, the different regions of the country cooperate a lot with each other. That only leaves "vertical" or social class distance as the dimension along which most inter-ethnic competition will be waged. Already during the twilight years of the Cold War, Americans didn't care about a potential battle between the USA and the Russkies -- they were more absorbed in the war between white trash and yuppie scum, as they called each other.

Perhaps this is the source of the red state - blue state mythology -- people want to engage in an Us vs. Them ethnic conflict based on "horizontal" distance, not just (or even primarily) based on "vertical" distance. But since there are no more Kaisers, Fuhrers, or Soviets, we had to invent a wide ethnic gulf. Surely we weren't going to pick any old way of splitting up the country, so we chose one with some plausibility -- after all, the data analyses so far do show that there is something to the red - blue stereotypes, even if they're profoundly exaggerated.

The other large source of horizontal ethnic conflict in America is based on allegiance to local sports teams. But this won't do very well because aside from a few teams like the Yankees, there aren't a handful of superpower teams that would provide as much dramatic conflict as the Allied vs. the Axis powers. Plus sports only appeal to a fraction of the population, so it would be hard to whip up everyone into a war mindset. But mention those latte-sipping liberals in blue states, or those low-IQ Biblical literalists in the red states, and suddenly everyone's passions become inflamed.

GSS variables used: race, region, wordsum, educ, visitart, dance, gomusic, drama

Class and religious fundamentalism in red vs. blue states

In the lead-up to and just after the last presidential election, much of the quant parts of the blogosphere were talking about Andrew Gelman et al's excellent book Red State Blue State Rich State Poor State. In it, they showed that increasing income predicted increasing likelihood of voting Republican, no matter if you live in a red state or blue state. The only catch was that this trend is more pronounced in red states, and more muted in blue states.

So, despite all of the red state vs. blue state mythology that people began telling each other during the past five or so years, rich people even in liberal blue states still tended to vote fairly Republican, and working-class people in conservative red states still tended to vote fairly Democrat. In fact, the split between red and blue states increased as you went up the income scale -- it seems that the culture wars of the 1990s were mostly an intra-elite competition.

I briefly jumped on the bandwagon and showed how an interest in hunting, fishing, and watching NASCAR fit this pattern. That is, it's mostly the lower-IQ people who do these things, regardless of whether they're in red or blue states, although for a given IQ level, red staters do have a greater interest. Still, a smart red stater is far less likely to care about hunting than a lower-IQ blue stater. IQ differences matter much more than red state vs. blue state differences.

After the election, interest in this topic naturally faded, which is unfortunate because there must be plenty of other examples of red state elites looking mostly like blue state elites, in addition to voting Republican and not caring about hunting or NASCAR. Of course, aside from voting patterns, the thing that's supposed to show the widest gulf between red and blue states is religion. But since we've seen that working-class people tend to vote Democrat, even in red states, we suspect that this other part of the conventional "red vs. blue" mythology is wrong. So let's turn to the General Social Survey to see how class and religious beliefs are related in both red and blue states. *

I'm looking here at fundamentalist religious beliefs, since that was the story -- not just that elite red staters went to church more often than lower-class blue staters, but that fundamentalist beliefs pervaded red state culture, while a staunchly secular mindset characterized blue state culture. The GSS measures such beliefs in two ways -- by asking if you think the Bible is God's word and is to be taken literally, and by asking if you know God exists without a doubt (the latter might not be so fundamentalist, but it's worth looking at too). I simply found the percent of each group who agreed with each of these statements.

I measured class in four ways, just to ensure that it doesn't matter which part of class we focus on -- socioeconomic index (a measure of job prestige), real income, education level, and IQ. The SEI bins are of size 5 and range from 17 - 22 through 92 - 97, real income is measured in 1986 dollars (in $5000 bins, centered on values ending in 5 or 0), education level is simply years of school completed, and IQ is the number of vocabulary words correct on a 10-question test.

Here are the plots for how religious fundamentalist beliefs are related to these measures of class, for both red and blue states (shown with red and blue lines, resp.):



No matter which belief we look at, and no matter which measure of class we choose, the same pattern shows up: the relationship between class and fundamentalism is more or less the same in red and blue states, namely that it declines pretty steadily as we move up the class ladder. The red - blue gap is roughly the same across the class spectrum, unlike voting patterns, where there was a widening of the gap as you moved up the income scale. In all cases, the upper-class red staters are well below the lower-class blue staters in fundamentalism. So, despite all of the rhetoric about godless blue states and Bible-thumping red states, fundamentalism is mostly a class-based phenomenon.

At the same time, the red lines are generally above the blue lines, showing that when we ignore class, red states are more fundamentalist than blue states. However, this overall red - blue gap is usually under 20% at most, whereas the drop from lower-class to upper-class fundamentalism is usually at least 30%. In other words, class distinctions trump red - blue distinctions.

The two pieces that fit with the reigning mythology are easy to see -- i.e., highly secular elites in blue states and highly religious working-class people in red states. But the problem of popular stories like the red state - blue state narrative is that we only see what agrees with them, while we blind ourselves to what clashes with them. In this case, no one saw that working-class people in blue states were highly religious and that upper-class people in red states were very secular. Rather than take a narrative for granted and look for data that support it (and ignoring those that refute it), we should simply take an empirical approach and look at all the data -- only then should we come up with the story, which by that point is just a common-language phrasing of what the data say, not some grand vision of how the world is presumed to be.

* I counted the following GSS regions as blue states:

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
Pacific - Washington, Oregon, California, Alaska, Hawaii

These regions are the red states:

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

GSS variables used: bible, god, sei, realinc, educ, wordsum, region

Climate and civilization among Blacks

In a previous post showing that colder climates favor civilization among Whites, I looked only at Whites in order to avoid a confound between climate and racial composition. (Razib's follow-up post showed the same trend even when looking at particular White ethnicities.) But now let's see what effect temperature has on degree of civilization among American Blacks. The data come from the same sources as before: average annual temperature, Audacious Epigone's estimates of average Black IQ by state (see his methods here) -- which this time include only 39 of the 48 continental states -- Statemaster's list of states by degrees awarded to non-Hispanic Blacks per capita, and this study on percent of non-Hispanic Blacks who are imprisoned. For these last two variables, there are data from all 48 continental states.

Here are the plots:




The Pearson correlation coefficient between heat and Black IQ is negative though not significant (r = -0.22, p = 0.19), although perhaps with reliable data on the 9 states left out, we might obtain a lower p-value. (The 9 states are all in the Northeast or northern part of the Mountain states, so unfortunately we're missing key data on how Blacks perform in pretty cold areas.) Nor is it significant between heat and percent of Blacks in jail (r = +0.03, p = 0.83).

However, it is significant between heat and degrees awarded to Blacks per capita, although in the opposite direction as for Whites -- hotter states award more degrees to Blacks per capita (r = +0.72, p = 7 x 10^(-9)). I don't think this is entirely due to the fact that most of the "historically Black colleges and universities" are in the Southeast, since hot and cold climates are also found in the middle and western parts of the country, and the pattern shows up there too.

It my seem strange that heat appears not to significantly affect average Black IQ, but here is another piece of evidence that Blacks and Whites do not respond equally strongly to the same the same climate. The Pearson correlation between Black IQ and White IQ across states is only +0.48 (p = 0.002, two-tailed). At least states with higher White IQ also tend to have higher Black IQ, but the agreement is not perfect. Note that the correlation between heat and Black IQ is not positive either -- as it would be if Blacks had higher IQs in the hotter climates that they're more biologically adapted to. Rather, the non-significant trend is what we see among Whites -- hotter climates are associated with lower IQs. In any case, below is a map of Black IQ. The only pattern I see is that coastal areas do better than inland areas.


We see something similar with the non-effect of heat on imprisonment rates of Blacks, whereas heat was significantly positively correlated with White crime. Again, the Pearson correlation between White and Black statewide imprisonment rates shows us that we shouldn't expect to see as strong of a relationship: it is +0.43 (p = 0.002, two-tailed), meaning that states with high White crime tend to have high Black crime, but the agreement is far from perfect.

Turning to the most significant result, it may seem odd that heat has the opposite effect on the per capita rate of degrees awarded to Whites vs. Blacks, though again the Pearson correlation between White and Black state degree rates shows that we should expect opposite effects: it is -0.40 (p = 0.005, two-tailed), meaning that states with higher rates of Whites earning degrees tend to have lower rates of Blacks earning degrees. As far as graduating college goes, Blacks appear to do much better in hot rather than cold environments.

So what do these new data on Blacks tell us? Mainly, that Blacks and Whites don't respond the same way to climate: heat either makes little or no difference among Blacks (IQ, crime) or actually helps Blacks (degrees), while it impairs Whites (IQ, degrees, and crime). I interpret this as further support for my contention that it is something about the climate per se that causes differences among Whites. Blacks are better adapted to hot climates than Northern Europeans, so they should not be as adversely affected by the insults of the hot climates that plague most of the US -- recall that Northern Europe lies north of America, while New York City lies at the same latitude as Barcelona and Rome.

Regarding mechanisms, if they have to do with heat per se, Blacks may become less fatigued or dehydrated by high temperatures. It's the middle of summer now, so you know how foggy your mind can get on a hot day. Furthermore, we already know that Blacks have built up a far greater suite of genetic defenses against infectious diseases, so they may be better protected against the myriad pathogens that are found more in the hotter parts of the US.

Lastly, it may seem counterintuitive that the colder climates appear not to encourage Black civilization so much, given all we're taught in school about the Harlem Renaissance and the blues of Chicago. But these outdated images may mislead us -- we ought to think more of Atlanta when we imagine a flourishing predominantly Black metropolis, to which Blacks have been returning in droves after living for decades in the northern US. Updating our picture of the Black world, these results don't seem so unbelievable after all.