Historical Variability in Heritable General Intelligence: Its Evolutionary Origins and Socio-Cultural Consequences Michael A. Woodley and Aurelio J. Figueredo University of Buckingham Press 2013, 112 pages.When Malthus analyzed the conditions that limited the growth of human populations in his time, his conclusions were clear: Those who were too poor could not afford to marry and raise a family. To prevent overpopulation and mass misery, they had to be counselled against marriage since celibacy was the only morally acceptable way to avoid offspring; and, of course, they had to be kept poor enough to prevent them from marrying. One century after Malthus, Francis Galton and his contemporaries woke up to the fact that the growth of European populations was no longer limited by the subfertility of the destitute, but by the deliberate avoidance of conception by the educated classes. At a time when Darwin's theory of evolution by natural selection was widely accepted by the intellectual elite and genetics was emerging as a new scientific discipline, the conclusion seemed obvious: Those heritable traits that cause people to acquire education and to limit their fertility will be bred out of the population. Galton introduced the term dysgenics to describe reproductive patterns like this, which favor the transmission of negatively valued traits.With the introduction of IQ tests in the first decade of the 20th century, the important heritable traits were increasingly identified with intelligence. Intelligence seemed to be the common denominator of both: children's ability to learn in school, and adults' ability to take control of their lives by limiting their reproduction. Studies performed in the 1920s and 1930s demonstrated two important facts that have been replicated numerous times ever since: (1) high heritability of IQ, and (2) a negative relationship between IQ and number of children. Therefore the expectation was that intelligence would decline from one generation to the next.It didn't happen. Based on the Scottish Mental Surveys of 1932 and 1947 and other evidence, Raymond Cattell and other researchers concluded that intelligence in Britain was rising, not declining. At the time, the phenomenon became known as Cattell's paradox. Today, the rising IQ trend that Cattell noticed in the 1940s is known as the Flynn effect, named after James Flynn who presented incontrovertible evidence of its widespread occurrence during the 1980s and recognized its general importance.The book by Michael Woodley and A.J. Figueredo is the most recent and, so far, the boldest attempt to grapple with Cattell's paradox. The traditional explanation is simple enough. Dysgenics has reduced intelligence slightly. Using the breeder's equation, which assumes that children are phenotypically between their parents and the pre-existing population mean depending on the (additive) heritability of the trait, the usual conclusion has been that dysgenics reduces the average population IQ by anywhere between 0.3 and 1.5 points per generation (summarized in Lynn, 2011). At the same time, massive environmental improvements, including better nutrition and health and an enormously expanded and intensified educational system, have raised intelligence. These environmental effects were about 10 times stronger than the genetic effects. The net effect of the two opposing trends was a large rise in intelligence, amounting to about 30 IQ points during the 20th century.Woodley and Figueredo break out of this mould by splitting intelligence into two components: heritable g, or general intelligence, and environmentally determined specialized abilities. The distinction is based on the well-established observation that, using factor analysis, the general ability factor g that is tapped by all cognitive tests is far more heritable than the more specialized abilities that are tapped by only some subtests of a complex IQ test battery (Jensen, 1998). We can think of gas the mental horsepower, or the quality of the neural substrate, and specialized abilities as the skills that people acquire by using this neural substrate. …