Twins: a test of the equal environments assumption

Area of Science:

• Behavioral Genetics
• Developmental Psychology

Background:

• Understanding the sources of environmental similarity in twins is crucial for behavioral genetics research.
• Previous research has not fully delineated the distinct contributions of parental treatment and twin-elicited factors to shared environments.

Purpose of the Study:

• To investigate the sources of shared environmental similarity in same-sex twin pairs.
• To examine whether monozygotic (MZ) and dizygotic (DZ) twins experience different levels of environmental similarity.
• To assess the relationship between environmental similarity and behavioral similarity in twins.

Main Methods:

• Surveyed 343 adult same-sex twin pairs on childhood and early adolescent social environment.
• Utilized factor analysis to identify sources of common environment.
• Compared environmental similarity between MZ and DZ twin pairs.
• Correlated environmental similarity with behavioral similarity (Neuroticism, Anxiety, Depression).

Main Results:

• The common environment of twins stems from parental "imposed" treatment and twins' "elicited" interests and behaviors.
• Monozygotic twins reported significantly more similar "imposed" and "elicited" environments than dizygotic twins.
• Similar "imposed" treatment was not associated with current behavioral similarity in either MZ or DZ twins.

Conclusions:

• Parental treatment imposed on twins does not confound the assessment of genetic and environmental influences on behavior.
• The twin method's validity is not threatened by imposed similar treatment based on zygosity.
• Distinguishing between "imposed" and "elicited" environmental factors offers a more nuanced understanding of twin development.