explain why . It is useful to recall that evolution is driven both by ran -
dom mutations and by the adaptive consequences of the mutation’s ex -
pression. If there are no consequences—if going bald doesn’t decrease
one’s chance of surviving and reproducing—then the mutation will bepassed on, even though it serves no useful function.
But we can at least speculate that there might have been an evolu -
tionary advantage in personality trait maturation. The main adaptive
tasks faced by adolescents are becoming independent adults, finding amate, and making a place in the world. Openness to Experience andExtraversion both make individuals more adventurous and help themexplore the natural and interpersonal worlds; they may thus be helpfulin solving the tasks of adolescents. Once settled in, however, with ahome, a mate, and a family to raise, these traits become less valuable—in fact, they may be distractions. Instead, love and work should now be -
come priorities, and these are related to Agreeableness and Conscien-
tiousness. It is less clear why adolescents should be high in Neuroticismcompared to adults, but it is hard to complain about its decline!
Cross-Cultural Evidence on Stability
Although we have noted from the beginning of this book that there ischange in personality traits during some portions of the lifespan, theemphasis has been on evidence of stability after age 30. In this chapterwe have argued that age differences seen in cross-cultural studies pro-vide another line of evidence that there are intrinsic maturational pat-terns in the mean levels of personality traits: From adolescence to fulladulthood, men and women decline in Neuroticism, Extraversion, andOpenness, and increase in Agreeableness and Conscientiousness. But docross-cultural studies also support the idea that changes after age 30 arerelatively small?
In general, yes. Averaged across the five factors and the five cul -
tures, the mean rate of change was about one-sixth standard deviation
per decade, and much of this change occurred in the first decade, be -
tween 18 and 30. However, there are some notable exceptions. In Figure
4, the Italian and Croatian data follow the American pattern closely , butthere appear to be substantial drops in Openness between the two old -
est groups in the Portuguese and Korean data. Here a cohort effect is
plausible, because in both Portugal and South Korea there are verymarked cohort differences in education. The oldest subjects in both96 PERSONALITY IN ADULTHOOD