Intelligence: A Very Short Introduction
by Ian J. Deary (1st Ed, 2001)
An expert's overview for the layman, describing how and why people differ in their thinking powers, Very data driven, and by necessity, largely driven by consideration of how to measure different aspects of intelligence, and therefore what aspects intelligence can be teased apart into, such as working memory, linguistic comprehension, perceptual organization, and speed of operation.
Each chapter tackles a key scientific question, describing the experiments that were done to determine the answers, showing the actual key experimental datasets.
Such questions include: Is intelligence determined by genes or the environment? The answer is 50/50, although surprisingly, little of the environmental influence is due to the family raising the child. Also, the effect of genetics increases with age.
How does a person's intelligence change as they age? Some skills show a straight decline from age 25 to 80, such as inductive reasoning, spatial awareness, perceptual speed and verbal memory. Other skills show a peak in middle-age, with only a small decline at high ages, such as verbal reasoning and numerical ability. The amount of mental decline with age is highly variable between different people. Those whose abilities decline the least have no cardio issues or chronic disease, have high social class, live in complex and stimulating environments, and are generally satisfied with life, and unstressed through middle age.
Does intelligence, especially as measured using existing tests, correlate with life outoutcomes such doing well at a job? Depending on the job, yes, a great deal. What sort of tests are good for predicting who will do well? Work samples, structured interviews, and psychometric tests all give slightly over 0.5 correlations. Which isn't stellar, but it's the best we've got. At the other end of the scale, graphology (handwriting) and age rankings had no correlation.
It's a short book, with a lively style, densely packed with important conclusions, and descriptions of how the field has arrived at them. Edifying.