personality . These differences, however, would reflect not the action of
aging but the accident of birth into a particular generation.
This confusion of generational or birth-cohort differences with age
changes is not merely hypothetical. There are a number of documentedcases in which cohort differences have been shown to be responsible forcross-sectional findings. Bones in the leg, for example, are typically a bitshorter in older men than in younger men. This is not a maturational ef -
fect, however, but a cohort effect (Friedlander et al., 1977): More recent
generations of children have had better diets and have as a result growntaller in childhood and adolescence. Somewhat closer to the topic athand, generational differences have also been shown to account formost of the age differences in vocabulary that have been reported(Schaie & Labouvie-Vief, 1974). Most vocabulary is learned in formalschooling, and today’s adults had much more of that than their grand -
parents did.
If we return to the cross-sectional studies we have reviewed, we
may now want to revise our conclusions. Perhaps the consistent declinein Extraversion is the result of changing styles of child rearing. Whenchildren were taught to speak only when spoken to, they may have de-veloped lifelong habits of reticence. The formal interactions of childrenwith their parents may have put a permanent damper on interpersonalwarmth and spontaneity . Thus, the older generation we see now may bemore introverted not because of age but because of what passed forgood breeding a few decades ago. Today’s outspoken, uninhibited chil-dren may turn out to be outspoken, uninhibited oldsters half a centuryfrom now.
On the other hand, it is also possible that very different processes
are going on under the camouflage of age differences. If there are suchsignificant changes in child rearing, shouldn’t we be seeing many andmassive age differences when we compare distant generations? Or is itpossible that the absence of conspicuous age differences is the result notof stability but of equal and opposite effects of aging and cohort? Thisperplexing idea, which plays a central role in many arguments about ag -
ing research, deserves a bit more discussion.
Suppose that, as progressives hope, the change in child-rearing
practices over the past 50 years has really had the beneficial effects thatit was supposed to: Suppose that today’s young adults are mentally andemotionally healthier than the young adults of 1930. Suppose furtherthat, in the process of living and learning how to adapt, all people tend66 PERSONALITY IN ADULTHOOD