PRETEND GENES 61correlate with their adoptive mothers’ IQs. Th is is then compared to the
correlation with their biological mothers. A higher correlation with the
latter is taken as evidence of the primacy of genes over environment.
Again, though, these are rough and ready observations that bear no
resemblance to properly controlled studies. As I pointed out in a review
article with Sarah Norgate, there are numerous reasons why adopted
children may appear to resemble their biological parents more than their
adoptive parents in IQ.^30
For a start, adoption agencies typically assign children to adoptive
families in a nonrandom way. Th ey tend to look for adoptive homes that
are “suitable,” in the sense of refl ecting the social class of the biological
mother. In contrast, adoptive parents tend to come from a narrow social
stratum. Th is restriction of range has the eff ect of reducing the estimate
of correlation between adoptees and adoptive parents. Here is a brief list
of other reasons adopted children may resemble their biological parents
more than their adoptive parents:
(a) Th e children’s average age at testing will have been closer to that of
their biological parents than of their adoptive parents (and test scores
change with age).
(b) Th e children will have experienced the infl uential environment
in the womb of their biological mothers, which can have durable eff ects.
(c) Power ful environmental eff ects on mothers, such as stress, can
alter gene expressions that are inherited by the children. Th ese can mu-
tually aff ect be hav ior, such as anxiety in test situations. Th ese eff ects are
described in chapter 4, and are mistaken for ge ne tic eff ects, even though
they are environmental.
(d) Adoptive parents have oft en been given information about the
birth family, which could have biased treatment and their expectations
of the child.
(e) Both the biological mothers (by virtue of their unwanted pregnan-
cies) and their adopted- out children will have reduced self- esteem and be
more vulnerable to challenging situations, like taking IQ tests. In that way
they in eff ect share environments.
(f) Some conscious or unconscious aspects of family treatment pol-
icy may prevail to make adopted children diff er ent from other adoptiveThis content downloaded from 139.184.14.159 on Tue, 17 Oct 2017 13:51:26 UTC