However, whereas Suber is a professional academic, I am not. Before reading any further, read my disclaimer and warning on my My Writings page.
Summary of The Bell Curve, Chapter 4
Glenn Mason-Riseborough (25/8/2002)
The Bell Curve: Intelligence and Class Structure in
American Life
Chapter. 4 Steeper Ladders, Narrower Gates
Richard J. Herrnstein & Charles Murray (New
York: The Free Press, 1996)
In this chapter the authors are talking about purported changes in American society (presumably of the US variety) during the 20th century, and making predictions about future trends. It is filling in some of the details that were mentioned in the introduction to Part 1 of the book.
The main claim in this chapter is that in the US there is an increasing social separation based on cognitive abilities. Cognitive abilities here is equated with intelligence, understood as a single factor g, and measured accurately by IQ tests. The authors call this social separation cognitive partitioning, and they say the members of the cognitive elite are becoming increasingly partitioned from the rest of society. With each generation this class structure is getting stronger, and during the 20th century there has been a progressively higher correlation between IQ, education, income, and social standing. There is some churning (movement between classes) but this is becoming progressively less. The authors predict that this trend will continue into the foreseeable future, and there is little that can be done about it.
Broadly, this is because of three factors:
(1) Social changes: There is, and has always been, this social separation to some degree. But changes in society are increasing this. Three aspects of society are mentioned:
(a) The education system is becoming increasingly egalitarian, and is increasingly providing equal opportunities for all children. I.e., fewer children are slipping through the system. As such, it is increasingly successful in sorting the high-IQs from the low-IQs in the society, and fewer of the cognitive elite slip through. Fewer of the cognitive elite are failing to gain college degrees, and the education system is producing more bright employable graduates.
(b) Wages for those with a high-IQ are disproportionately higher than wages for those with a low-IQ, compared with previous generations. Members of the cognitive elite are becoming more sought-after and businesses are prepared to pay more for them.
(c) There is physical segregation in the sense that members of the cognitive elite live, work, play, shop, worship, and study together, and they tend not to meet up with the rest of society. Recently, new technological fields, new ways of doing business, and greater urbanisation are increasing this segregation.
(2) Assortative mating: This is the idea that there is a natural disposition for people to marry like-minded others. A 1943 study showed that for 1000 engaged couples there was a positive correlation for all 51 traits measured, and the correlations were significant for all but six. Most studies indicate this correlation is highest for IQ, at around .4. There is also a suggestion that this propensity to marry someone of a similar IQ has increased as sexual equality has increased.
(3) Heritability of IQ: Cognitive abilities are determined partly genetically and partly environmentally (however, the evidence currently indicates that the environmental component is primarily not shared family environments, but environmental influences experienced by individuals as individuals). Currently, based on hundreds of studies, heritability of IQ is estimated at .6 ± .2 (for identical twins raised in separate homes it is as high as .75 to .8, and for ordinary siblings raised in separate homes it is lower but rarely below .4). In addition, the authors suggest it may be higher than this for older people, since the heritability of IQ rises as one gets older, and most studies were done on younger people. Further, the more general the measure of intelligence – the closer it is to g – the higher is the heritability. Finally, in societies where there are high variations in exposure to education the heritability of IQ is lower. As environments become more uniform the heritability increases, and as a consequence children resemble their parents more and become more different from people in other families. Given educational egalitarianism, all US children have a chance to develop their latent cognitive abilities and currently in the US the environmental factors are fairly low. So, in the US differences in intelligence are determined to a greater degree than ever by genetic differences, not environmental differences. And more than likely this will continue to increase as the society becomes even more egalitarian.