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Adolescent-Typical Behavior Patterns 11variety of species often entering adolescence sooner and males tending to lagsomewhat behind (see Spear, 2000, for discussion and references).Although ontogenetic periods corresponding to adolescence can be identifiedin nonhuman animals, these other species of course do not demonstrate the fullcomplexity of brain, behavior, or psychopathology evident during human adolescence(or at any other time of life). Nevertheless, there are notable commonalitiesbetween human adolescents and their counterparts in other mammalianspecies in terms of developmental history and genetic constraints, as well as intheir behavioral predispositions and neural and hormonal characteristics. Suchsimilarities may have been driven in part by common evolutionary pressures.Among the behavioral proclivities characteristic of adolescents of a variety ofspecies are an increasing focus on peer-directed social interactions, increased interactionswith peers, and occasionally increased fighting with parents relative toyounger and older individuals (Csikszentmihalyi et al., 1977; Primus & Kellogg,1989; Steinberg, 1989). Also common among mammalian adolescents are increasesin behaviors termed novelty seeking, sensation seeking, risk taking, andimpulsivity (Adriani et al., 1998; Trimpop et al., 1999). Behavioral commonalitiesseen among adolescents from a variety of species presumably are rewardingand highly conserved because of their ultimate adaptive significance. For instance,peer-directed interactions have been shown to be particularly rewarding duringadolescence in research using an animal model (Douglas et al., 2004) and havebeen shown to support development of new social skills and social support (Galef,1977; Harris, 1995). Novelty, likewise, appears especially rewarding for adolescents(Douglas et al., 2003), with risk taking postulated to serve a number of adaptivefunctions, such as increasing the probability of reproductive success in malesof a variety of species, including humans (Wilson & Daly, 1985). Risk taking mayalso be adaptive for the adolescent by providing opportunities to explore adultbehaviors and privileges (Silbereisen & Reitzle, 1992) and to face and conquerchallenges (Csikszentmihalyi & Larson, 1978).Increased affiliation with peers and elevated risk taking may also supply theimpetus for maturing male and female adolescents to explore new areas awayfrom the home. Emigrating with peers away from the home area around the timeof sexual maturation to territory far from genetic relatives is a common strategyused among mammalian species to avoid inbreeding and the lower viability ofresulting offspring due to greater expression of recessive genes (Bixler, 1992;Moore, 1992). Indeed, in virtually all species of mammals (including our humanancestors, e.g., Schlegel & Barry, 1991), male adolescents, female adolescents,or both emigrate away from the home territory prior to sexual maturation, a journeyoften taken with peers (e.g., Keane, 1990). Even in modern human societies,in which cultural traditions largely protect against inbreeding and hencereduce emigration pressure, adolescent risk taking still persists, not only becausesuch traits may be retained for quite some time under relaxed selection pressure