The Building Hypothesis
The second central claim of the broaden-and-build theory is that experiences of positive emotions, through their broadening effects, build people’s enduring personal resources. Indirect evidence consistent with this building hypothesis can be drawn from correlational and experimental studies of humans and animals that link positive traits and states and behaviors linked with positive states-such as play-to increases in physical, intellectual, and social resources. As previously indicated, ethologists who have observed nonhuman mammals have associated juvenile play with the development of specific survival maneuvers evident in both predator avoidance and aggressive fighting (Boulton & Smith, 1992; Caro, 1988), suggesting that play builds enduring physical resources. Reinforcing this claim, laboratory experiments that have deprived rats of juvenile social play have shown that, compared with nondeprived controls, deprived rats were slower to learn a complex motor task (Einon, Morgan, & Kibbler, 1978). Evidence suggesting that positive emotions build intellectual resources can be drawn from studies on individual differences in attachment styles.