Hockenbury Discovering Psychology 5th txtbk

Adolescence395Table 9.3The Typical Sequence of PubertyGirlsAverageAgeOvaries increase production of 9estrogen and progesteroneInternal sex organs begin to 9 1 ⁄2grow largerBreast development begins 10Peak height spurt 12Peak muscle and organ growth, 12 1 ⁄2including widening of hipsMenarche 12 1 ⁄2(first menstrual period)First ovulation 13 1 ⁄2(release of fertile egg)AverageBoysAgeTestes increase production 10of testosteroneExternal sex organs begin 11to grow largerProduction of sperm and first 13ejaculationPeak height spurt 14Peak muscle and organ growth, 14 1 ⁄2including broadening of shouldersVoice lowers 15Facial hair appears 16Source: Based on data in Brooks-Gunn & Reiter (1990).Factors Affecting the Timing of PubertyAlthough you might be tempted to think that the onset of puberty is strictly amatter of biological programming, researchers have found that both geneticsand environmental factors play a role in the timing of puberty. Genetic evidenceincludes the observation that girls usually experience menarche atabout the same age as their mothers did (Brooks-Gunn & Reiter, 1990;Ersoy & others, 2005). And, not surprisingly, the timing of pubertalchanges tends to be closer for identical twins than for nontwin siblings(Mustanski & others, 2004).Environmental factors, such as nutrition and health, also influence the onsetof puberty. Generally, well-nourished and healthy children begin pubertyearlier than do children who have experienced serious health problems or inadequatenutrition. As living standards and health care have improved, the averageage of puberty has steadily decreased in the United States over the past century.For example, 150 years ago the average age of menarche in the United States wasabout 17 years old. Today it is about 12 1 ⁄2 years old. The same downward trend isalso evident in boys. Compared to the 1960s, boys today are beginning the physicalchanges of puberty about a year earlier (Herman-Giddens & others, 2001;Irwin, 2005). In recent years, however, the trend toward earlier puberty seems tohave slowed (see Parent & others, 2003).Body size and degree of physical activity are also related to the timing of puberty.In general, stout or heavy children begin puberty earlier than do lean children. Girlswho are involved in physically demanding athletic activities, such as gymnastics, figureskating, dancing, and competitive running, can experience delays in menarcheof up to two years beyond the average age (Brooks-Gunn, 1988).Interestingly, the timing of puberty is also influenced by the absence of the biologicalfather in the home environment. Several studies have found that girls raisedin homes in which the biological father is absent tend to experience puberty earlierthan girls raised in homes with intact families (Bogaert, 2005a; Ellis & Garber,2000; Hoier, 2003). Researcher Brian Mustanski and his colleagues (2004) foundsimilar results for both sexes in a large-scale study of more than 1,800 pairs of twins.In that study, both boys and girls raised in father-absent homes experienced acceleratedphysical development.Other studies have revealed that the quality of family relationships is tied to thetiming of puberty. The pattern that emerges is that negative and stressful familyenvironments are associated with an earlier onset of puberty, including earlier“Dad, when will I be old enough to shave?”© The New Yorker Collection 1995 Michael Crawford fromcartoonbank.com. All Right Reserved.