J.P. Rushton reports:
Winick et al.  studied 141 Korean children malnourished-in-infancy and then adopted as infants by American families. They found that by 10 years of age the children exceeded the national average in IQ and achievement scores: A severely-malnourished group obtained a mean IQ of 102; a moderately-nourished group obtained a mean IQ of 106; and an adequately-nourished group obtained a mean IQ of 112.We know that genetic differences among races have some part in explaining why they perform differently on IQ tests. The question is what is the best estimate of the heritabile component of the gaps? Exactly "0%" for all race gaps everywhere is not a serious answer scientifically, but is rather evidence of one closing oneself off from evidence and being driven entirely by ideological pre-conceptions.
Anti-hereditarians who want their fixed a priori position to appear scientific and not purely a derivative of their ideological commitments will thus resort to ad hoc argumentation. "In argumentation, an ad hoc argument is one that is hastily constructed to support or explain something without any underlying sense or logical framework. Because of this haste and lack of a consistent frame-work, the explanation is likely to contradict existing thought or other arguments. Usually it happens if someone is put on the spot to explain something - they can either deal with it in a consistent manner (meaning that their arguments are consistent for all eventualities so far), change their consistent beliefs to match, or produce an ad hoc explanation off-the-cuff to dismiss it" (http://rationalwiki.org/wiki/Ad_hoc).
The following is excerpted from Robert J. Sternberg's Handbook of Human Intelligence: