focusing on different ways that brain development relates to adolescent risk-taking.

Adolescence Across Species

Developments in the brain relate to important features of adolescence, not only among humans but also among other mammals, Spear explained. The gradual transition from dependence and immaturity to relative independence and maturity is one that virtually all mammalian species experience. Humans and other species need to develop the skills necessary to survive as adults and to reproduce.

During this transition phase, mammals experience many hormonal and physiological changes, such as growth spurts and puberty, and they tend to display certain behaviors that are typical of the age. Spear noted that human behavior and brain function are significantly more complicated than those of other mammals—and also cautioned against interpreting these observed phenomena as evidence of biodeterminism, because many other factors affect human development and behavior. Nevertheless, across species, adolescents tend to show increases in preference for socializing with their peers, which researchers think may be adaptive behavior that helps individuals develop social skills, supports the skills they will need as adults, and helps them prepare to survive without parental protection. Adolescents in a variety of species also show increases in novelty-seeking and risk-taking, which, for humans, often are expressed through the behaviors discussed in Chapter 2. Researchers have posited, however, that the propensity to seek novelty and take risks may be adaptive in several ways. For males in particular, these impulses may improve the odds of reproductive success. They may foster acceptance among peers, and they may help the species avoid inbreeding by making males, females, or both more likely to leave their home territory by the time they are sexually mature, so they can seek mates elsewhere and avoid inbreeding.

The biological changes that occur in mammals also include puberty, a period when a cascade of hormonal activity, beginning with the release of gonadotropin from the hypothalamus gland, culminates in the release of the gonadal hormones estrogen and testosterone. These hormones, in turn, have a variety of effects on the body and on behavior, Spear explained. At the same time, however, equally dramatic changes in the brain are taking place.

Brain Structures

Spear pointed out that the basic structures of the brain are relatively ancient from an evolutionary perspective. Thus, virtually all mammalian

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