Longitudinal behavior genetic analyses of problem behavior and cognition
Researcher:
Ms. M.J.H. (Marjolein) Rietveld
The
study explores the relative contribution of genes and environment to the
development of intelligence and behavior problems in young children. Both
aspects of the study cover a longitudinal design. More than 200 twin pairs are
tested with a Dutch intelligence test at the age of 5, 7 and 10 years old (RAKIT;
Bleichrodt, Drenth, Zaal, & Resing, 1984). Initial analyses of the
5-year-old data showed a moderate degree of covariance between verbal and
nonverbal cognitive abilities. It was found that this observed covariance was
accounted for by environmental aspects, shared by children from the same home
(“home environment”). Subsequent analyses revealed that the home environment
became negligible in explaining variance between children, whereas genes became
an important source of variation at the age of 10. Stability of cognitive
performance from age 5 to 7 to 10 was influenced by genes, much more so than by
environmental influences.
The second
part of the study is focused at the development of children’s behavior, and
the contributing role of genes and environment. Persistence of behavior is a
function of the type of behavior. That is, aggressive and oppositional behavior
is much more stable compared to withdrawn and anxious behavior. The stability or
lack of stability is accounted for predominantly by genes. However, the
influence of the home environment should not be disregarded when explaining
variation in children’s behavior. It appears that over time the home
environment becomes more important in accounting for the observed variation.
A third aspect of the study is directed at the overlap between intelligence and behavior problems. Unfortunately, variation in problem behavior displayed by the participating twins is too small to detect any interesting covariance between the variables at all.