Beware the plausible hypothesis

So I read Richard Lynn's book. He makes a rather convincing argument for the position that there are significant genetic differences in intelligence among different races. And yet, his argument is almost certainly wrong, and makes a good case study in how difficult it can be to properly interpret data. I'll start by restating Lynn's argument. In fact, I'll go Lynn one better and make an argument that is even stronger than the one he makes. Then I'll show you why it's (almost certainly) wrong.

Let us begin by observing that it is entirely uncontroversial that intelligence has a significant genetic component. Humans are more intelligent than any animal and that is clearly due to the fact that we're humans. Furthermore there are well understood genetic deficiencies in humans (like Down syndrome) that result in marked mental retardation. Furthermore, Down syndrome is also associated with distinctive and easily recognizable physical characteristics, so we have at least one example of a genetic mutation that causes changes is both intelligence and physical appearance. So the hypothesis that there are differences in intelligence among races and that those differences are genetic cannot be ruled out a priori (the way we can, say, claims of perpetual motion) since we have an uncontroversial existence proof that such phenomena do indeed occur.

Furthermore, it is uncontroversial that humans have migrated over periods of time long enough to induce genetic differences among populations. It is clear that differences in skin color is an evolutionary adaptation that has occurred in response to environmental pressures. Lactose tolerance is another very recent example, having evolved as recently as 3000 years ago so even creationists can sign on to that one :-)

Lynn begins his argument by observing that, "There is a widespread consensus that intelligence is a unitary construct that determines the efficiency of problem solving, learning, and remembering." He goes on to give a brief history of the definition of intelligence (which is too long for me to quote here), IQ, and the Flynn effect. He then devotes an entire chapter to discussing the concept of race, addressing the modern notion that the concept of race is a "myth" and showing that even those who advance that view acknowledge that races, as is intuitively obvious to everyone by the most doggedly politically correct, do indeed exist.

The rest of the book is a seemingly unassailable mountain of data showing an indisputably clear and consistent correlation between race and intelligence (as measured by IQ scores). He then shows that intelligence is almost entirely (75-80% depending on the study) a genetically inherited trait by citing studies of identical twins reared apart. Finally, he proposes a plausible mechanism (the evolutionary pressure of having to survive winter) for producing the observed differences in intelligence.

Have I convinced you? There is at least one glaring flaw in the argument above which I introduced on purpose in order to make a point. You might want to see if you can spot it before going on.

BTW, if you are convinced you shouldn't feel bad about it. It's a very convincing argument, and it might even be correct. (It might even be correct despite the flaw.) I am not aware of any data that would falsify it. But it is nonetheless almost certainly wrong. Here's why.

Let's start with my motivating example, Down syndrome, which is indeed a genetic disorder that produces both profound mental retardation and easily identifiable physical traits. However, while Down syndrome is genetic, it is not inheritable. Down syndrome results when an individual gets an extra copy of chromosome 21, which happens during meiosis or gestation. In fact, if you trust Wikipedia (which you really shouldn't, but what the hell) the non-inheritability of Down syndrome leads some researchers to use parents of children with Down syndrome as controls for studies of autism which is apparently at least partially heritable.

So the fact of the matter is that there are no precedent phenomena for the claim that there are genetic differences that result in correlated mental and physical differences within a species. (Obviously there are such differences across species.) This is not to say that it doesn't happen, just that if it happens it is not common. The a priori plausibility of the claim is much lower than the above argument would lead one to believe.

I introduced the Down syndrome argument as a deliberate red herring to make the point that even glaring flaws in an argument are not always immediately obvious even when you are primed for them. Lynn's argument has no flaws quite so glaring as that one (he's not a crackpot). Instead, Lynn's argument contains lots and lots of little flaws that together add up to an argument that is almost certainly wrong. Let's start to explore those.

The foundational flaw in Lynn's argument is the claim that intelligence "is a unitary construct", that it can be reduced to a single number (IQ), that that number can be reliably measured, and that the resulting measure has a causal relationship to something of consequence like the ability to survive winters or build industrial economies. If you read closely, he doesn't actually provide any evidence that this is the case (because there isn't any), he only says that "there is a widespread consensus." Now, this is actually true. There is indeed a widespread consensus. But just because there is a widespread consensus does not mean that it is actually true. As recently as a few decades ago there was a widespread consensus that homosexuality was a mental disease. At various times in history one could find a widespread consensus that bleeding, thalidomide, and Vioxx were effective treatments for various ailments.

In fact there is no evidence that IQ tests measure anything beyond a person's ability to do well on an IQ test. And there is a good reason for this. There are some cognitive abilities (like short term memory capacity, visual acuity, and spatial reasoning) that can be measured objectively, just as we can objectively measure certain physical abilities (like raw strength and speed). But the applicability of these abilities to real-world situations is limited. The holy grail of intelligence testing is a person's overall ability to solve novel problems, and therein lies the rub because a novel problem can only be novel once. I do really well on IQ tests but that's because I'm a geek and I spent a lot of time solving puzzles when I was a kid. I'm really good at solving puzzles, and particularly good at solving the kinds of puzzles that people tend to put on IQ tests. But it is far from clear whether my puzzle-solving skill is a result of some innate ability that I have, or whether it's simply because I've had a lot of practice. There is no way to know which way the causality runs.

It's like this for any kind of complex skill. Is Tiger Woods a superior golfer because he has the golfing gene (and does he have it because of or despite the fact that he's black), or is it simply because he's been golfing continuously since he was three? To really find out you'd need to do an experiment with a statistically significant number of subjects all going through the same intensive training that Tiger Woods went through, and even then you wouldn't really know because it's possible that one kid has a lot of innate golfing skill but just doesn't like golfing enough to really apply herself. The number of factors that go into making an effective golfer or an effective computer programmer or an effective businessman or an effective politician or even an effective puzzle solver are so diverse and varied that it would be impossible to design a study that could tease all these factors apart and give you a statistically significant result.

It gets worse. If you're testing the hypothesis that genes cause both dark skin and decreased "intelligence" (whatever that means) it is impossible to create a control group because it is impossible to hide the fact that a person with dark skin has dark skin. It is therefore impossible to eliminate the subtle effects of societal prejudices. Even if we take all of Lynn's data at face value, all we've shown is that people with dark skin don't do as well on IQ tests as people with light skin. But this could simply be due to the fact that people with light skin happen to live under circumstances that are conducive to the development of IQ-test-taking skills. And I don't just mean better economic conditions, I mean a pervasive belief shared by light-skinned and dark-skinned people alike that light-skinned people are somehow superior. Such a belief can become a self-fulfilling prophecy, and the problem with self-fulfilling prophecies is that they are actually fulfilled. Such beliefs can become self-reinforcing because they are actually true but not because of anything genetic, rather they are true simply because people believe them, rather like a mass (anti-)placebo effect.

None of Lynn's data refutes the self-fulfilling-prophecy hypothesis. Indeed, the widespread acceptance of Lynn's conclusions despite his obvious scientific sloppiness (like mistaking consensus for fact) lends support to it.

The problem is that there is no way to experimentally resolve this. To do so you would have to have a way to make black people look like white people (or vice versa), and that's just not possible. So at this point we have two equally plausible hypotheses to explain the data. How do we decide between them? And in particular, how do I justify my claim that Lynn is "almost certainly wrong"?

Well, let's look at the data. The first thing you notice is that the actual numbers are not nearly as consistent as Lynn would have you believe. To cite just one example that I found leafing through the tables, his data for Zambia are based on two studies, one of which puts the average IQ of Zambians at 77 and the other at 63, very nearly a full standard deviation of difference. And such discrepancies are not unusual.

But let's leave that aside for a moment and take Lynn's data at face value. Consider the unfortunate inhabitants of Cameroon, with an average IQ of 64. Or Equatorial Guinea with an average of 59. These figures are so low as to fall into the range of mild mental retardation. Compared to the Chinese at the opposite extreme with an average IQ of 105 the difference is more than two standard deviations. That seems like an implausibly high variance to be due to genetic factors. To be sure, differences of this magnitude in physical traits are certainly possible -- skin color comes to mind as an example -- but they are rare, and intelligence is much more complex than melanin production.

There's a lot more that could be said about this (and has been but I don't have time to write a treatise. I'll just point out one more problem with Lynn's methodology, one that is more serious than any I have cited so far.

On page 5 of Lynn's book he writes:


The metric employed for the measurements of intelligence f the races has been to adopt an IQ of 100... for Europeans in Britain, the U.S., Australia and New Zealand as the standard in terms of which the IQ's of other races can be calculated. The mean IQ's of Europeans in these four countries is virtually identical.


Notice anything oddly coincidental about those four countries? In all four, English is the native language. So Lynn's definition of intelligence, his gold standard, is the performance of English-speaking people on IQ tests. Don't you think that this definition might introduce just the teensiest bit of cultural bias into the whole endeavor? Besides the winter-induced-genetic-drift hypothesis and the self-fulfilling-prophecy hypothesis we can introduce a third plausible theory to explain Lynn's results, that "intelligence" is just a measure, at least in part, of the ability to learn to speak English. How well do the data support this theory? Well, the Chinese data seems to refute this, but how to explain e.g. the Lithuanians, who at an average IQ of 90 are significantly below their anglophonic cousins? And Lithuania is not exactly known for being a tropical paradise. If having to deal with winter makes you smart, why aren't the Lithuanians geniuses? Why are the Chinese so much smarter than the Innuit? Why are Italians smarter than the Portugese? In these last two examples the differences are huge: a full standard deviation.

The fact of the matter is that intelligence is a monstrously complex phenomenon governed by both genetics and environmental factors. The hypothesis that genetics are the dominant factor, and that adaptation for survival in winter is the driving force, is not in fact supported by the data. And in fact there is one final argument that I think puts the final nail in Lynn's argument: if intelligence is so crucial to winter survival, why do we not see the same differences in intelligence in animals? Why is it that the most intelligent land animals (great apes and elephants) evolved in Africa and not in Europe?

I am open to the possibility that the neo-eugenicists might still be correct. But until someone comes up with a much better argument than Lynn's (and Lynn's is the best they have) anyone who advances the position that blacks are genetically inferior to whites is a bigot in my book.