Inheirited IQ? Yes And No
The question -- do genes or environment matter for IQ? There are two answers: Genes if you're rich and well-fed. If you're poor, environment matters.

In the WSJ, Matt Ridley writes about my friend Dr. Nancy Segal's book, Born Together - Reared Apart, about the landmark Minnesota Twins study on identical twins separated at birth. The findings are fascinating:

Today, a third of a century after the study began and with other studies of reunited twins having reached the same conclusion, the numbers are striking. Monozygotic twins raised apart are more similar in IQ (74%) than dizygotic (fraternal) twins raised together (60%) and much more than parent-children pairs (42%); half-siblings (31%); adoptive siblings (29%-34%); virtual twins, or similarly aged but unrelated children raised together (28%); adoptive parent-child pairs (19%) and cousins (15%). Nothing but genes can explain this hierarchy.

But as Drs. Bouchard and Segal have been at pains to point out from the start, this high heritability of intelligence mainly applies to nonpoor families. Raise a child hungry or diseased and environment does indeed affect IQ. Eric Turkheimer and others at the University of Virginia have shown that in the most disadvantaged families, heritability of IQ falls and the influence attributed to the shared family environment rises to 60%.

In other words, hygienic, well-fed life enables people to maximize their genetic potential so that the only variation left is innate. Intelligence becomes significantly more heritable when environmental hurdles to a child's development have been dismantled.

I haven't read the book Ridley reviewed, but I was very moved and compelled by Nancy's other recently published book, Someone Else's Twin: The True Story of Babies Switched at Birth. It's about Canary Islands girls -- one twin and one non-twin -- who were given to the wrong parents at the hospital, and who only found out at age 28 through a chance encounter at a store at a mall. Sadly, the discovery ruined some lives.