They might not be able to change careers or shell out for a sports car, but chimpanzees and orangutans may experience midlife crises much the same as humans do.
A well-documented phenomenon in people, the midlife crisis was thought to set in after optimism about future possibilities gives way to recognition of our own mortality. But now scientists are trying to understand if a biological factor is involved as well after a study of 336 chimpanzees and 172 orangutans discovered the apes' moods sagged around the midpoint of their expected life spans. Less likely to engage socially in middle age, the apes showed the same “U”-shaped curve in happiness from birth to death as people.
While not conclusive, the study does suggest that social explanations alone might be insufficient to describe the causes of a midlife crisis. Hormones, brain structure, or neurochemicals might play an important role, too.