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Philosophers and psychologists alike have long debated the etiology of beliefs about human agency. Recently, empirical investigations have shown that lay beliefs about free will and determinism represent stable and important individual differences. Despite a perennial interest in the sources of agentic belief, genetic and environmental influences on such beliefs have never been studied. We administered a battery of items assessing these beliefs to a unique sample of 394 adoptive and biological families with adult offspring to investigate the origins of agentic beliefs and their relationships. We found significant differences between adopted and biological offspring and between the parents of such children, particularly in beliefs about determinism. Biometric modeling revealed especially surprising results: unlike the vast majority of traits studied in family designs, agentic beliefs appear to be weakly or not at all heritable. Since genetic factors might be regarded as typical of the "initial conditions" in philosophical thought experiments about free will and determinism, it is especially ironic that beliefs about free will and determinism may be among the traits least influenced by genetic differences.
Willoughby et al. (Thu,) studied this question.