Gladwell seems to overlook the findings from Dan Seligman's book "A Question of Intelligence", when attributing Asian math performance to rice cultivation and Jewish success in law on being born in NYC in 1930.

Seligman notes the above average performance on jewish people on the verbal component of psychometric tests. The recent paper by Cochran & Harpending on Ashkenazi Jewish intelligence indicated there was a genetic basis for this:

"What accounts for this remarkable record? A full answer must call on many characteristics of Jewish culture, but intelligence has to be at the center of the answer. Jews have been found to have an unusually high mean intelligence as measured by IQ tests since the first Jewish samples were tested. (The widely repeated story that Jewish immigrants to this country in the early 20th century tested low on IQ is a canard.) Exactly how high has been difficult to pin down, because Jewish sub-samples in the available surveys are seldom perfectly representative. But it is currently accepted that the mean is somewhere in the range of 107 to 115, with 110 being a plausible compromise.

The IQ mean for the American population is “normed” to be 100, with a standard deviation of 15. If the Jewish mean is 110, then the mathematics of the normal distribution says that the average Jew is at the 75th percentile. Underlying that mean in overall IQ is a consistent pattern on IQ subtests: Jews are only about average on the subtests measuring visuo-spatial skills, but extremely high on subtests that measure verbal and reasoning skills."

The three authors conclude this part of their argument with an elegant corollary that matches the known test profiles of today’s Ashkenazim with the historical experience of their ancestors:

The suggested selective process explains the pattern of mental abilities in Ashkenazi Jews: high verbal and mathematical ability but relatively low spatio-visual ability. Verbal and mathematical talent helped medieval businessmen succeed, while spatio-visual abilities were irrelevant.
The rest of their presentation is a lengthy and technical discussion of the genetics of selection for IQ, indirect evidence linking elevated Jewish IQ with a variety of genetically based diseases found among Ashkenazim, and evidence that most of these selection effects have occurred within the last 1,200 years."

In terms of East Asian math/science performance, Seligman notes they tend to perform above average on the non-verbal component of psychometric tests which is consistent with the math/science performance:

"Severely compressed, his explanation goes about like this: Some sixty thousand years ago, when the lee Age descended on the Northern Hemisphere, the Mongoloid populations faced uniquely hostile "selection pressure" for greater intelligence. Northeast Asia during the Ice Age was the coldest part of the world inhabited by man. Survival required major advances in hunting skills. Lynn's 1987 paper refers to "the ability to isolate slight variations in visual stimulation from a relatively featureless landscape, such as the movement of a white Arctic hare against a background of snow and ice; to recall visual landmarks on long hunting expeditions away from home and to develop a good spatial map of an extensive terrain." These, Lynn believes, were the pressures that ultimately produced the world's best visuospatial abilities."