Not in Our Genes: Biology, Ideology, and Human Nature
Cat Island in the Bahamas maintains a declining population of one thousand or so by slash-and-burn agriculture. Few of the one-room houses have electricity; none has plumbing. The local teacher, a British expatriate, told me that in seven years only one child had managed to win entrance into the two-year program at the College of the Bahamas in Nassau—and that she had flunked out. When I asked why, he gave a perfectly obvious and reasonable answer: how can Cat Island children maintain any interest or time for studies? They come home late in the afternoon; they have to haul water, care for the goats, help to prepare food. After dinner, they have no place (or light) for doing homework. I nodded in evident agreement, but his next statement startled me (this, I should add, was a casual barroom conversation; he knew me only as a peculiar snail collector, not as author of The Mismeasure of Man). We now know, he said, that only 20 percent of mental ability is environmental; 80 percent is inherited, so these immediate factors can explain, at most, one-fifth of the under-achievement. The rest must be genetic, probably caused (he opined) by inbreeding among the few families that inhabit Cat Island.
Lee Kuan Yew, the prime minister of Singapore, has raised a furor in that distant land by suggesting that the genetic stock of his nation is about to plummet. He studied his census figures and noted a trend common to all developed nations: highly educated women are having fewer children than women with little schooling. Although this fact usually (and correctly) inspires no action beyond a call for more education (both for its intrinsic merits and for its salutary impact upon population), Lee gave the argument a discredited eugenic twist that has not been heard for the past half century or so: uneducated women are genetically inferior in intelligence and their likeminded offspring will swamp the smaller pool of intrinsically bright children born of educated parents. Lee acknowledged that environment and upbringing can influence both access and success in education, but we now know, he continued, that 80 percent of intelligence is fixed by inheritance, and only 20 percent malleable by circumstance. “A person’s performance,” Lee stated, “depends on nature and nurture. There is increasing evidence that nature, or what is inherited, is the greater determinant of a person’s performance than nurture (or education and environment)…. The conclusion the researchers draw is that 80 percent is nature, or inherited, and 20 percent the differences from different environment and upbringing.”
The fallacies of this and other hereditarian arguments about complex human social behaviors have been so thoroughly rehearsed that scholars might be tempted to treat any new discussion with undisguised boredom. In the case of IQ, estimates of heritability are a confusing mess, ranging from the notorious 80 percent, long cited by Jensen and based originally upon the faked research data of Sir Cyril Burt, to Leon Kamin’s argument that existing evidence …