Saturday, July 22, 2006

Intelligence, nature and nurture

Some new data on genetic vs environmental influences on IQ in this recent Times magazine article. Until recently, twins studies could only examine the effect of environmental variation within a limited range -- from working to upper class -- because very poor families are generally not allowed to adopt babies. The effect of family background has been found to recede to almost nothing by late adulthood in these twins studies, but the possibility that severe deprivation might have a stronger effect has not been ruled out. Recent investigations, as detailed below, have focused on very poor families and found a significant effect. We might characterize this as discovering the non-linear region of gene--family environment interaction :-)
NYTimes: A century’s worth of quantitative-genetics literature concludes that a person’s I.Q. is remarkably stable and that about three-quarters of I.Q. differences between individuals are attributable to heredity. This is how I.Q. is widely understood — as being mainly “in the genes” — and that understanding has been used as a rationale for doing nothing about seemingly intractable social problems like the black-white school-achievement gap and the widening income disparity. If nature disposes, the argument goes, there is little to be gained by intervening. In their 1994 best seller, “The Bell Curve,” Richard Herrnstein and Charles Murray relied on this research to argue that the United States is a genetic meritocracy and to urge an end to affirmative action. Since there is no way to significantly boost I.Q., prominent geneticists like Arthur Jensen of Berkeley have contended, compensatory education is a bad bet.

...When quantitative geneticists estimate the heritability of I.Q., they are generally relying on studies of twins. Identical twins are in effect clones who share all their genes; fraternal twins are siblings born together — just half of their genes are identical. If heredity explains most of the difference in intelligence, the logic goes, the I.Q. scores of identical twins will be far more similar than the I.Q.’s of fraternal twins. And this is what the research has typically shown. Only when children have spent their earliest years in the most wretched of circumstances, as in the infamous case of the Romanian orphans, treated like animals during the misrule of Nicolae Ceausescu, has it been thought that the environment makes a notable difference. Otherwise, genes rule.

Then along came Eric Turkheimer to shake things up. Turkheimer, a psychology professor at the University of Virginia, is the kind of irreverent academic who gives his papers user-friendly titles like “Spinach and Ice Cream” and “Mobiles.” He also has a reputation as a methodologist’s methodologist. In combing through the research, he noticed that the twins being studied had middle-class backgrounds. The explanation was simple — poor people don’t volunteer for research projects — but he wondered whether this omission mattered.

Together with several colleagues, Turkheimer searched for data on twins from a wider range of families. He found what he needed in a sample from the 1970’s of more than 50,000 American infants, many from poor families, who had taken I.Q. tests at age 7. In a widely-discussed 2003 article, he found that, as anticipated, virtually all the variation in I.Q. scores for twins in the sample with wealthy parents can be attributed to genetics. The big surprise is among the poorest families. Contrary to what you might expect, for those children, the I.Q.’s of identical twins vary just as much as the I.Q.’s of fraternal twins. The impact of growing up impoverished overwhelms these children’s genetic capacities. In other words, home life is the critical factor for youngsters at the bottom of the economic barrel. “If you have a chaotic environment, kids’ genetic potential doesn’t have a chance to be expressed,” Turkheimer explains. “Well-off families can provide the mental stimulation needed for genes to build the brain circuitry for intelligence.”


Anonymous said...

If such IS the case then are we to discriminate individuals based on the category of I.Q. they fall into?

If Indians and East-Asians generally do well in so-called intelligence-measuring tests should we automatically confer on them a higher status within our society?

While the factual information presented may (and I emphasize... may!) lead one to that supposition, the fact remains we still don't possess the level of understanding regarding the basic mechanisms of intelligence (beyond general information from neuroscience studies) to make any "scientific" conclusions.

As for the general level of "under-achievement" among black students within our educational system, just compare that to the level of achievement of exchange-students from Africa. This would help us to understand that the "racial" categorification of individuals may not be a readily applicable procedure, atleast in-so-far as an entire population may be concerned.

And to conclude, some of the brightest minds in the world of software-engineering come from villages in India. How are they able to achieve world-class standards of intellectual achievement if they happen to be relatively less opportunate than fellow counterparts within the US? Do the experts have any concensus on this?

Steve Hsu said...

That IQ tests are measuring something "real" about people, which has something to do with general cognitive ability, seems well supported by data. See references here , in particular US military experiences with recruit training and IQ scores.

The meaning of significant group differences in IQs remains to be seen. For example, averages in most third world countries (including Africa and S. Asia, but not E. Asia) are lower than in the US, Europe, Japan, etc. If Turkheimer is right it may be due to poverty, and not so much due to any genetic differences.

Finally, most top scientists and engineers I meet from India come disproportionately from elite families -- often, parents are doctors, professors, civil servants, etc. I suspect poverty is hurting young minds in India just as it is in other countries.

Let's hear it for Grameen bank!

Anonymous said...

Anonymous said...
If such IS the case then are we to discriminate individuals based on the category of I.Q. they fall into?

If Indians and East-Asians generally do well in so-called intelligence-measuring tests should we automatically confer on them a higher status within our society?

Dear Anonymous, This would only be the case if you make the choice to value inteligence over personhood, personality, determination, and other factors that may have more value to society than IQ. That would be a choice based on your morals and has nothing to do with science or this research.

Peter D.

Unknown said...

Some problems with the Turkheimer study:

1 - The study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid. The effects of the shared environment vanish at around age 12.

2 - Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.

3 - Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.

4 - Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no adult IQ correlation between biologically unrelated children who were reared together in the same home.

5 - Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used "cannot determine which aspect of SES is responsible for the interactions" observed.

Blog Archive