An even shorter introduction to intelligence

I recommend Ian Deary’s Intelligence: A Very Short Introduction. I am going to buy more books in this Oxford series. We at Marginal Revolution aim to provide value for attention, however, so here is an even shorter introduction.

1) Almost all measures of intelligence correlate with one another and quite a few measures of different aspects of intelligence are highly correlated. It is thus meaningful to talk about general intelligence, g. Howard Gardner’s work on “multiple intelligences” is on the fringes of scientific psychology.

2) Intelligence rankings are stable with age but fluid intelligence, meaning something like pure reasoning power, as opposed to crystalized intelligence peaks in the 20-30s and then declines with age.

3) Connecting IQ scores to brain morphology and activity is still in its infancy but there are modest, but well established, correlations between brain size and IQ (psychometric intelligence) and measures of reaction time (which plausibly measure brain speed) and IQ.

4) Intelligence is in large part genetic and that which is due to environment is primarily not due to the obvious possibilities such as family upbringing.

5) Intelligence matters for work performance and education. IQ is a better forecaster of work performance than just about any other test short of a trial run on the actual work to be performed.

6) IQ has been rising, the Flynn effect. No one knows why.

7) None of the above points are controversial among intelligence researchers.

Aside from Dreary’s book another useful introduction to intelligence research is the authoritative consensus report from the American Psychological Assocation, Intelligence: Knowns and Unknowns, summary here.