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


As recently as the Middle Ages, teenagers were considered adults as soon as they reached sexual maturity. Then they became eligible for marriage. For example, Juliet in Shakespeare's Romeo and Juliet was 13 years old.

What are secondary sex characteristics?

The biological changes of adolescence are triggered by sex hormones. The sex hormones bring on changes collectively known as secondary sex characteristics: appearance of body hair, breast development in females, muscle development in males, and enlargement of the voice box producing a deeper voice in males.

What behavior is correlated with high testosterone levels in teenage boys?

Hormones also have behavioral effects. The male hormone, testosterone, causes increased aggression in all primate species, including humans. In humans, high testosterone levels correlate with "rebelliousness, talking back or fighting with classmates" (Howard, 1985). Seemingly this should explain the rebelliousness of adolescent boys, and perhaps it does in some cases. However, research shows that the stereotype of rebellious adolescence is somewhat misleading.

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