PRETEND GENES 55same neighborhood, remained friends, sat next to each other in school,
and so on. Some even returned to live with each other in adulthood.
We cannot be sure how well the MISTRA twins were, in fact, sepa-
rated, because full details have never been published. Th e investigators
do mention in an early report that “circumstances of adoption were some-
times informal” and that “time together prior to separation” was 0–48.7
months— that is, members of at least some of the pairs had spent as much
as four years together before being separated. We also know that at least
some of these “separated” twins later had reunions and spent consider-
able amounts of time together.^18
Th e consequences for purportedly objective study are obvious. However
vague psychologists are about environments impor tant for similarities in
IQ, anyone might suspect that something about families, neighborhoods,
schooling, and contact time would be among them. But there are other
prob lems.
Th ey Are Not Representative
Th e twin samples should be typical of the general population in the sense
of covering all environmental factors and their pos si ble eff ects. Lack of
true separation already breaches that condition. But so do other pecu-
liarities of the MISTRA. Twins generally tend to be self- selecting in any
twin study. Th ey may have responded to advertisements placed by inves-
tigators or have been prompted to do so by friends or family, on the
grounds that they are alike. Remember, at least some of them knew each
other prior to the study. Jay Joseph has suggested that the twins who
elected to participate in all twin studies are likely to be more similar to
one another than twins who chose not to participate. Th is makes it dif-
fi cult to claim that the results would apply to the general population.
Results Are Not Fully Reported
Fi nally, the experimental results have been partially and selectively
reported. For example, of two IQ tests administered in the MISTRA,
results have been published for one but not the other. No explanation
is given for that omission. Could it be that they produced diff er ent
results?
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