If there is a correlation between parent IQ and child IQ, it's not necessarily because the child inherited it. High IQ parents are going to provide a different environment for their child than parents that are more average. For instance, more books, more advanced language and discussions, more strategy games, more enrichment activities--because those are things they find important or interesting. IQ in children seems to be highly variable depending on the environment they are in. That being said, there seems to be a genetic component as well but the research out there doesn't show it to be the only thing when it comes to looking at the IQs of children. My two are completely genetically unrelated and their IQ profiles are strikingly similar. They both have PRI scores that are in the 140's and lower verbal scores. They both have processing speed scores that are signficantly lower. What are the odds that would occur if you randomly took 2 kids off the street and compared their scores? The similarities in their scores probably have a lot to do with being in the same environment. I gave birth to both of them, so there could also be a prenatal effect.
The scores of older kids/adults seem to align more closely with what you'd expect to see in terms of genetics. A lot of people seem to forget that scores can change over time when kids are tested.
, genetics plays the major role in IQ when SES is at a level necessary to achieve self-actualization. Below that SES threshold, environment becomes the major determinant.
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.
