In the new The New Republic, Steven Pinker does a fair and thorough assesment of the recent study asserting that Ashkenazi Jews have a genetic advantage in intelligence. According to the researchers (Gregory Cochran, Jason Hardy, and Henry Harpending), this selection took place from about 800 A.D. to 1600 A.D, when Jews in Northern Europe were relegated to being moneylenders and estate managers. Of course, rapid selection produces unintended side-effects, and Cochran, et.al. argue that the price of a higher IQ was Tay Sachs and Gaucher's disease, which are highly prevalent among Ashkenazi Jews.
Needless to say, this is an audacious hypothesis. Pinker ably dissects the controversy into 7 smaller controversies. He spends the most time analyzing the last link in the chain, which is that the common Ashkenazi diseases are by-products of the same genes that enhance intelligence.
So the evidence that Ashkenazi disease genes boost intelligence is extremely iffy. Still, the hypothesis is testable: compare the IQs in a large sample of sibling pairs, one of whom is a carrier of a disease gene, the other a non-carrier. If the carriers are not smarter, the hypothesis is wrong. The study could easily be done in Israel, with its centralized records of health care, education, and military service.
After all the ink that's been spilled on this relatively minor paper, it's nice to have some new testable ideas put forward, and I hope someone starts sifting through Israeli hospital records. Pinker's conclusion on the evidence as a whole is equally fair:
The researchers have provided prima facie evidence for each of the hypotheses making up their theory. But all the hypotheses would have to be true for the theory as a whole to be true--and much of the evidence is circumstantial, and the pivotal hypothesis [that increased intelligence led to Tay-Sachs] is the one for which they have the least evidence. Yet that hypothesis is also the most easily falsifiable. By that criterion, the CH&H story meets the standards of a good scientific theory, though it is tentative and could turn out to be mistaken.
Pinker spends the last third of the article ruminating on the perils and possibilities of human genetics. It's here that he begins to make less sense. Take this silly sentence:
Someday someone could test whether there was selection for personality traits that are conducive to success in money-lending and mercantilism, traits that I will leave to the reader's imagination.
I hate to rain on the parade of future geneticists, but I sincerely doubt that we'll ever find the genes responsible for success in money-lending. (Although there might be a used-car salesman gene...) Why not? Because I doubt there is a specific collection of heritable traits that confers success on merchants, bankers, or other middlemen. I've met a few bankers and stock-brokers in my day (the modern equivalent of money-lenders), and I can firmly attest that they were all very different people, and didn't seem infused with a common collection of habits and traits.
Predictably enough, Pinker is for tearing down "these politically comforting shibboleths (such as the non-existence of intelligence and the non-existence of race)" because "reality is what refuses to go away when you do not believe in it." Sure. Sounds swell. But it's also worth remembering why these shibboleths became politcally comforting in the first place. After all, there has been no shortage of past scientific data asserting all sorts of fallacious links between biology, race and intelligence. And I'm not just talking about Nazi phrenology. Many well intentioned scientists, from Broca to Bruce Lahn, have seen their neat theories of genetic causation slowly unravel.
What's the moral? Before we start searching for investment banker genes, or imagining all sorts of causal links between Ashkenazi Jews and IQ, it's worth remembering what we still don't know. Although it's been several years since the completion of the Human Genome Project, we still can't find the scraps of DNA responsible for schizophrenia, or autism, or most other major mental illnesses. This isn't because we haven't been looking; it's because finding these genes is so damn hard. So why don't we take it one step at a time. Why don't we start with unambiguous personality traits (like schizophrenia) and, after we've located the dozens of genes underlying madness, work our way up to studying much more subtle quirks of the cortex, like intelligence and race?
I understand that "The Bell Curve" shows that Scots and Ashkenazim are
smarter than everyone else. I haven't tried to evaluate the evidence, but it
seems oddly compelling to me, also to my Simpson cousins. :-)
It would get real complicated fast if intelligence were an interaction among disparate genes. Add diet and pathogens to the soup and its going to take an army of geneticists to sort out.
Why don't we start with unambiguous personality traits (like schizophrenia) and, after we've located the dozens of genes underlying madness, work our way up to studying much more subtle quirks of the cortex, like intelligence and race?
It's far from clear that schizophrenia is a less complex phenomenon than intelligence. In fact, the opposite may be true. In the first instance, schizophrenia isn't an 'unambiguous personality trait' (it's not really a personality trait at all); it's a severe, pervasive, and extremely heterogeneous mental disorder. Some individuals exhibit positive symptoms (e.g., hallucinations, delusions, etc.), others exhibit only negative symptoms (flat affect, apathy). Some people have a single psychotic break and make a full recovery; others are doomed to an institutionalized life. One of the biggest problems schizophrenia researchers face is deciding just how to categorize all the different manifestations of schizophrenia. It's not even clear yet whether it's a spectrum disorder, a qualitatively different state, or a collection of disorders of unrelated etiology that happen to have overlapping phenotypic expressions. In general, if you were to ask for a 'simple' psychological phenomenon, I think schizophrenia would be one of the last items on most researchers' lists.
Contrast that with intelligence. The many manifestations of intelligence, which reliably load very highly on a single underlying factor (the so-called 'G'), popular notions of multiple intelligences notwithstanding. You can take almost any two measures intuitively thought to tap intelligence and odds are they'll be positive correlated. Typically, fluid G accounts for anywhere between 30-70% of the variance in zero-order measures. That's huge, and suggests that there are likely to be a relatively small number of factors contributing to variations in general intelligence. For example, brain volume alone (and particularly prefrontal volume) accounts for about 10% of the variance in gF scores. Now I'm certainly not suggesting intelligence is simple; but I do happen to believe (as I suspect plenty of other researchers do) that intelligence will prove to be easier to understand than a disorder like schizophrenia. If we were to take it one step at a time, we'd never get anywhere. It's good for scientists to keep in mind that the issues they deal with are complex, but only up to a point.
I was looking through some recent research on children's intelligence lately, and found this interesting. The strongest predictor of childhood IQ is parental expectations for grades (about 30% of variance). This is much stronger than parental education and social status, and holds even at younger levels (before school habits are firmly established).
There's so much 'folk knowledge' and mythology about intelligence and the manifestations, that the notion of actually testing reasonable hypotheses seems radical.
Stewart, do you remember where you saw that study? It sounds interesting.