This is the 2007 version. Click here for the 2017 chapter 10 table of contents.

Summary: Adolescence, Adulthood and Aging

The biological changes of adolescence are triggered by sex hormones. The male hormones, such as testosterone, lead to increases in aggression, not just in humans but in all primate species. However, the stereotype of the rebellious adolescent is exaggerated, according to researchers. Among teenagers, the vast majority is not rebellious. In fact, they are quite well adjusted.

The environment of an adolescent affects the typical experiences of teenage years. Urban teens are more likely to get involved with gangs and antisocial activities. Suburban teens often feel strong cooperative pressures. Rural teenagers may feel isolated and make plans to get away. In urban and suburban areas, it is common to find teenagers preparing to enter a profession similar to a parent. There are several possible reasons for this, including genetic and environmental influences.

William James wrote that personality is "set like plaster" by the age of 30, and long-term research by psychologists tends to back him up. Western culture of the 1960s and 1970s emphasized the possibility of radical changes in direction during adulthood, but this is the exception to the rule.

Jack Block followed a group of people from their early teen years through middle age. He found that on almost every rating scale there was a "striking pattern of stability." Two studies involving adults aged 25 to 82 found the same thing. Personality and attitudes remained stable. The most stable trait of all was shyness.

Sometimes the adult characteristics of people change not because of individual factors but generational factors. These are called cohort effects, a "cohort" being a group of people born around the same time. One important cohort effect has involved changing social roles of women. The "traditional" family shown in 1950s television situation comedies is now a statistical minority, as people have waited longer before getting married, had fewer children, and more women have entered the workplace.

Intellectual strengths change with age. Old people are almost always at their peak in the morning hours. Young people are more likely to feel that their peak time of the day is in the afternoon, evening, or night. Young people excel at "flexible intelligence." They can learn new things more quickly than old people. Old people excel at "crystallized intelligence." They can use an accumulation of experience to solve problems.

There are various theories about what causes aging. The premature aging syndrome (progeria) suggests a genetic basis to aging. Children with this disorder look like little old men or women by age 11. Studies show this syndrome is due to a defect in only one gene, suggesting that there is a genetic system that normally regulates or suppresses age-related changes.

The idea that aging is due to an accumulation of genetic errors is supported by the finding that telomeres, "caps" on the end of DNA strands, are shorted each time a cell divides. Eventually the DNA becomes frayed and the cell becomes senescent. An enzyme called telomerase repairs the telomeres. When a telomerase-generating gene is inserted into cells that ordinarily do not have it, the cells become "immortalized." Currently, however, the only known technique for extending the lifespan is to go hungry. This makes all organisms from yeast to mammals live longer. . A substance that has the same effect without requiring starvation, resveratrol, is the subject of much research.

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