Topic 8: Behavior Genetics

Possible readings to consider for Day 1

As required readings:

• Deary's Intelligence, pp. 67-90 (Datasets 7-9).
• Eysenck ("Nature and nurture.."). His diagram on how parents at different IQ levels produce children across a wide span of the IQ distribution is extremely important for understanding why genetic differences in IQ guarantee much social mobility in any society where merit counts in who gets ahead.

There is SO MUCH in this topic that is important. We must first make clear the logic of how scientists estimate heritability and environmentality. Then there are all the surprising findings about the genetics of intelligence, including that: (1) the heritability of intelligence rises with age and, correspondingly, environments have less and less effect during development on who is brightest or dullest; (2) differences in family environments have no lasting effect on intelligence, but the environments NOT shared by siblings do (that is, non-genetic factors make siblings less alike in IQ—not more alike—that their genes alone would predict); (3) beliefs, attitudes, and socioeconomic outcomes are somewhat to moderately heritable; and (4) even our environments themselves tend to be somewhat heritable, that is, products of our genes (e.g., how we are raised, how much social support we get, etc.). If there is any topic in intelligence that turns our ideas upside down, the genetics of intelligence is it.

One possible focus for Day 2 is to look at how the heritability of intelligence ensures a moderate degree of social inequality but only a moderate degree. In any free society, genetic differences in IQ guarantee much social mobility across generations. This counterintuitive fact is explained in one section of Eysenck’s chapter. It is a surprising idea for most people. It is also a very important one we need to touch on at some point, because it explains why so much social policy has counterproductive consequences.

Useful handouts:

• Worksheet on shared and non-shared effects. Having groups work on this worksheet during class has been a good way for students to catch on to the idea of shared vs. non-shared environments. Families are important, but not in the way we usually think.
• Sample data on heritability of attitudes and life events. These 3 pages of findings are useful for having students speculate about how our genetic predispositions help shape our environments and to illustrate the idea of “niche-seeking.”

Other readings (or parts thereof) to consider:

• Bouchard (“Whenever the Twain Shall Meet”) Provides more details about identical twins reared apart, discusses them as clones, and more. SECOND PASSWORD NEEDED IS 6335 (ignore any subsequent error messages and click “OK”) NOTE: IF YOU CAN’T DOWNLOAD THE ARTICLE HERE (there is a glitch I still need to fix), GO TO ELECTRONIC RESERVES. IT’S THERE TOO.
• Plomin & Petrill article (“Genetics and Intelligence: What’s New?”) in your grey-red Intelligence journal. Parts may be useful for further background.

Resources to consider

• Various videos on twin and adoptee research

Organizational questions for you to think about

• What are the key facts and procedures in the readings—the crucial building blocks—do you think the class needs (or needs special help) for understanding your topic? This is important especially for Day 1.
• What issue or question do you want to focus on in Day 2, and how?
• What is its instructional purpose?
• How will your activity help accomplish that purpose?