IQ and Class

...the class structure of modern society is essentially a function of the innately differing intellectual and other qualities of the people making up these classes....................H. J. Eysenck, The Inequality of Man


It can hardly escape notice that this analysis is exceedingly convenient for those in posistions of power and privilege in society, expecially for those engaged in promoting policies to protect those privileges through favorable tax and other policies. It's also a fact that Eysenck's view is widely held among the dominant strong hereditarians in the intelligence testing community. This view was codified by Herrnstein and Murray's influential book: The bell curve: Intelligence and class structure in American life, and promoted by others such as Steven Pinker.

They argue that music lessons, preschool, and all the other activities parents try to promote their children's intelligence are essentially pointless, since IQ is determined by heredity and essentially immutable.

This view has long been attacked by left leaning biologists such as Steven Jay Gould, but I never found their arguments persuasive. Richard E. Nisbett's Intelligence and How to Get It is a different tale. Unlike Gould, Nisbett digs into the twin and adoption studies that established the strong hereditarian view and exposes their weaknesses. Even more importantly, he reports on a large number of well designed studies which tell a vastly different story. I will mention a couple of points in the following.

The cardinal weakness of the twin and adoption studies is that they failed to account for non-genetic correlations in the adopting families. Other studies which carefully consider diversity of adoptive environments reach different conclusions. Also very importantly, as Nisbett points out, heredibility of a trait is relative to the population and environment in which it is tested. High hereditability says nothing about the limits of the influence of environment. Height is one of the traits highest in hereditability, but changes in nutritional patterns have produced two to three standard deviation increases in adult height in some countries.

Multiple lines of evidence show that a similar mutability applies to IQ, especially (and quite ironically) to those aspects of IQ called "fluid intelligence," long touted as "culture free." More details later - or read the book yourself.

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