The resolution of cultural and biological inheritance: informativeness of different relationships.

The informativeness of different relationships for resolving the genetic and cultural transmission of a continuous variable is explored by computer simulation. Extended twin, extended nuclear-family, and adoption designs are considered. Combining data on twin and parent-offspring pairs provides a powerful means of detecting genetic and cultural transmission. The addition of uncle-nephew and first-cousin data sometimes leads to an increase in power. Designs involving monozygotic twin pairs and their offspring are weaker. The most powerful adoption designs involve data on both biological parent-adopted-away offspring and adoptive parent-adopted offspring pairs. In the absence of information about biological parents, combining nuclear-family, adoptive parent-adopted offspring, and adoptive/natural sibling relationships still provides a powerful strategy for hypothesis testing. Adoption designs are more robust than extended twin and extended nuclear-family designs for resolving cultural and biological inheritance in the presence of genetic dominance or phenotypic assortative mating.