The glass is half full and half empty: A population-representative twin study testing if optimism and pessimism are distinct systems

Optimism and pessimism are associated with important outcomes including health and depression. Yet it is unclear ifthese apparent polar opposites form a single dimension or reflect two distinct systems. The extent to which personalityaccounts for differences in optimism/pessimism is also controversial. Here, we addressed these questions in a geneticallyinformative sample of 852 pairs of twins. Distinct genetic influences on optimism and pessimism were found. Significantfamily-level environment effects also emerged, accounting for much of the negative relationship between optimism andpessimism, as well as a link to neuroticism. A general positive genetics factor exerted significant links among both per-sonality and life-orientation traits. Both optimism bias and pessimism also showed genetic variance distinct from alleffects of personality and from each other.