Progress in EvolutionNovember 23, 2009

[IanC]

For example, given average cognitive ability and age, the odds of having reported a job limitation because of health were about 3.3 percent for white men working in white-collar jobs compared to 3.8 percent for white men working in blue-collar jobs, a very minor difference. But given that both men have blue-collar jobs, the man with an IQ of 85 had double the probability of a work disability of a man with an IQ of 115.

Rushton continues on to say that as environments haven been becoming more equalized, the differences in health and life expectancy between classes has been growing. In England in 1930, the lowest social class had a 31% higher chance than the highest class of dying at each age. By 1971 it was 61% and in 1981 150%. Part of the explanation for this (mine, not Rushton’s) is that IQ became a better predictor of social class over the 20th century.

It’s quite remarkable what a powerful explanatory force g is. The Bell Curve shows that it’s a better predictor for how one will do on a job than a test specifically designed to measure skills needed for the work. If a skills test does predict well, it’s usually because it taps into g. Considering what it means for humans, it’s little wonder that nature would time and again select intelligence and anything that goes with it across a wide range of species.

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You don't need IQ tests to measure intelligence.