Jerome Kagan in an older article (Policy ??) finally found 20-some cases of
twins who had been raised by different "parents" who also fell into different
socio-economic groups. There were so few because adoptive agencies &
others directly concerned try to match natural and adoptive parents.
Anyway, if memory serves, he found IQ differences between THESE twins of
up to 2 std. deviations. The big place to gather twin data is Japan
where twins are normally separated. But rarely reported!
Given these Kagan data, I will stick with Artie Goldberger who estimated
(depending upon uncheckable but entirely plausible assumptions) that the
genetic component is somewhere between zero and 40%. Notice that Kagan
claims a genetic component to at least one aspect of "personality" but
states that there seems to be no IQ (whatever is thus measured)
difference associated with "inhibited" as opposed to "uninhibited"
youngsters.
______________________________________________________________________________
John Buttrick [EMAIL PROTECTED]
Economics Dept. and CERLAC Phone: (416) 977-8329
York University Fax: (416) 977-1706
North York, Canada M3J 1P3
