Richard Nisbett: Intelligence mostly varies due to the environment, not genes

March 31, 2009 | By | 4 Replies More

The dominant hereditarian view of intelligence holds that intelligence is mostly fixed by the genes.   Richard Nisbett has dismantled the evidence on which the hereditarian theory is based.   In his new book, Intelligence and How to Get It, Nesbitt argues that the twin studies on which the hereditarian view is based are deeply flawed.  The main problem is that the adoptive homes in which those separated twins often find themselves are uniformly enriched learning environments.  Nisbett’s book was reviewed by Jim Holt of the NYT Book Review:

Nisbett bridles at the hereditarian claim that I.Q. is 75 to 85 percent heritable; the real figure, he thinks, is less than 50 percent. Estimates come from comparing the I.Q.’s of blood relatives — identical twins, fraternal twins, siblings — growing up in different adoptive families. But there is a snare here. As Nisbett observes, “adoptive families, like Tolstoy’s happy families, are all alike.” Not only are they more affluent than average, they also tend to give children lots of cognitive stimulation. Thus data from them yield erroneously high estimates of I.Q. heritability. (Think: if we all grew up in exactly the same environment, I.Q. differences would appear to be 100 percent genetic.) This underscores an important point: there is no fixed value for heritability. The notion makes sense only relative to a population. Heritability of I.Q. is higher for upper-class families than for lower-class families, because lower-class families provide a wider range of cognitive environments, from terrible to pretty good.

What does Nisbett’s book have to say about race and intelligence?  That the differences among the “races” are not genetic.   Evidence in point:  The “racial” IQ gap has been shrinking.   “Over the last 30 years, the measured I.Q. difference between black and white 12-year-olds has dropped from 15 points to 9.5 points.”


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Category: Bigotry, Current Events, Education, ignorance, Psychology Cognition

About the Author ()

Erich Vieth is an attorney focusing on consumer law litigation and appellate practice. He is also a working musician and a writer, having founded Dangerous Intersection in 2006. Erich lives in the Shaw Neighborhood of St. Louis, Missouri, where he lives half-time with his two extraordinary daughters.

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  1. Dan Klarmann says:

    One question I'd like to see tackled is about the effect prenatal environment has on characteristics like intelligence and aggressiveness. The gestation period is undeniably developmentally crucial, and dependent on the genes, upbringing, and current behavior of the mother alone.

    This potent environment falls into the fuzzy gap between zygotic genetics and post-natal upbringing.

  2. Josh says:

    "Heritability of I.Q. is higher for upper-class families than for lower-class families, because lower-class families provide a wider range of cognitive environments, from terrible to pretty good."

    Nisbett overlooks studies that contradict this and the study by Turkheimer he relies on involved children aged under 7. That is long before the shared environmental component disapears.

    This type of error is frequent throughout Nisbett's book: he often "proves" that environment matters more to IQ than previously thought by citing studies of young children. It is only when we reach adulthood that the full effect of our hereditary factors occurs, so estimates of the heritability of intelligence ought to be based on adult IQ scores.

    A Theory-Based Review of the Research in Richard Nisbett's Intelligence and How to Get It

  3. Please read our latest book "Between the Rhetoric and Reality" Lauriat Press;Simpkins&Simpkins,2009…It lends to the subject being discussed..

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