Genetic and Environmental Influences on Preschool Sibling Cooperation and Conflict

SUMMARY

With a sample of 524 pairs of three to eight year old twins recruited from a population registry, sibling cooperation and conflict were linearly related to the level of temperamental difficulty expressed in the twin dyad. Heritability accounted for 75% of the variance in Difficult Temperament, 0% of the variance in Instigating Cooperation, and 41% of the variance in Instigating Conflict. The shared environment, on the other hand, accounted for 0% of the variance in Difficult Temperament, 61% of the variance in Instigating Cooperation, and 28% of the variance in Instigating Conflict. Genetic influences largely accounted for the association between temperament and the sibling relationship. Using identical twin difference scores, Sibling Cooperation was one aspect of the nonshared environmental influence on temperament. Parental Positivity and Parental Negativity predicted the sibling relationship above and beyond temperament. Thus, the behavior genetic design elucidated the etiological distinctions among these correlated family variables.

Key Words:

• Genetics
• temperament
• siblings