Adoption studies including adopted-apart parents and offspring and adopted
–apart siblings show genetic influence on intelligence.
An example of developmental genetic analysis involves a longitudinal adoption study.
Colombo conducted a study in 1992 on school-age children (5-21
years). The first group consisted of children who were placed for adoption before 12 months and were raised by adoptive
families; the second group consisted of children who were raised in their birth families. The purpose was to compare the IQ of adopted children
with that of their nonadopted birth siblings and also compare the IQ of the
adopted children with the IQ of their biological siblings and with IQ of the birth parents.
Results showed that the IQ of adopted children became
more similar to the IQ of their birth parents with increasing age.
A second example was done by O’Connor in 2000 on Romanian adopted children in the UK. The purpose was to examine whether adopted children show better cognitive development
than their birth siblings who stayed behind in a deprived environment. They
tested the cognitive development of adopted children who stayed behind compared to that of their nonadopted siblings in an
enriching adoptive family and school environment.
Findings show that the adopted-away children showed higher IQ
scores than their nonadopted siblings who stayed behind. However it also showed that adopted children scored less in school achievement compared
to their environmental siblings. This shows us that both genetics and environment plays a role in intellectual
potential.
