The Influence of Family on Psychological Development: Behavioral Genetics Perspective
Introduction
The question of how much our upbringing and parents shape us psychologically is a common one. While personal anecdotes suggest a strong influence, and many professional organizations emphasize the importance of parents, the field of behavioral genetics offers a different perspective.
Conflicting Views: The Role of Parents
Most people, scientists, and child development experts believe families are important. Some, like Plato, Marx, and Engels, have even suggested abolishing the family to promote social goals and equality. However, behavioral geneticists, represented by figures like Robert Plomin, argue that genetic similarity, not shared family environment, is the primary reason for resemblance between family members.
Plomin posits that family environments are fungible, meaning that children will turn out similarly regardless of their specific family environment. This contrasts sharply with mainstream beliefs.
Origins of the Behavioral Genetics Perspective: Twin Studies
The behavioral genetics view stems from twin studies. Pioneer John Loehlin conducted twin studies in the 1970s when psychologists were skeptical about genetic influences on behavior. These studies aimed to determine if genetics played a role in personality differences.
Loehlin's unexpected findings from twin studies, particularly regarding the similarity of twins, laid the foundation for the field's perspective. The Minnesota Twin Family Study, initiated in 1990, further explored these patterns by studying both parents and twins longitudinally.
Interpreting Twin Study Results: Genetics, Environment, and Shared Environment
Twin studies analyze the similarity (correlation) between monozygotic (MZ) and dizygotic (DZ) twins to infer the importance of genetics and environment.
Genetic Influence: Indicated by the difference in correlation between MZ and DZ twins.
Non-shared Environment: Environmental factors that siblings growing up in the same home do not share. Evidenced by the fact that MZ twins, despite being genetically identical, are not perfectly similar.
Shared (Common) Environment: Environmental factors shared by siblings growing up in the same home, such as parental influence. The formula to determine the effects of shared environment is expressed as:
Loehlin's perplexing observation was that in many studies, twice the DZ twin correlation was less than the MZ twin correlation, suggesting a minimal impact of shared environment.
Adoption Studies: A More Direct Approach
To directly assess the impact of family environment, adoption studies compare similarities between adopted siblings. In the Minnesota Adoption Study, researchers examined 617 families, including those with both kids adopted, full biological siblings, and one child genetically related and the other adopted to directly test the effect of the shared environment.
By comparing traits of non-genetically related siblings raised in the same home, researchers can directly estimate the proportion of variance associated with the common rearing environment. The correlation between adopted siblings directly estimates the proportion of variance associated with their common environment (shared rearing).
Findings from Adoption Studies: Personality vs. Social Values
Data from adoption studies using the Multidimensional Personality Questionnaire (MPQ) showed low correlations between adopted siblings for most personality traits. However, the
most personality traits. However, the studies indicated that some social values and attitudes might be influenced more by the shared environment. This suggests that while our genetic background does play a crucial role in shaping our personality, the environment we grow up in may still have significant effects on our beliefs and values. These findings highlight the complexity of human development and the need to consider both genetic and environmental factors when examining personality and behavior.