American Ethnic Diversity in Age at Menarche
An analysis of menstrual status data obtained from a nationally representative sample of 2,510 girls, ages 8 to 20 years, found significant ethnic differences in age at menarche (Chumlea et al., 2003). This analysis provided estimates of the median ages at which 10%, 25%, 50%, 75%, and 90% of the population had attained menarche for each of three ethnic samples: White Americans, African Americans, and Hispanic Americans. The data, summarized in ■ Table 12.2, reveal that African American girls start to menstruate earlier than girls in the other two ethnic groups. This difference is significant when compared with White girls at the age levels at which 10%, 25%, and 50% of the girls had started menstruating. In terms of statistical significance, Hispanic American girls began menstruating earlier than White girls only at the 25% level.
■ TABLE 12.2 Age at Menarche (in Years) for Selected Percentiles of U. S. Girls
|
Percentile |
|||||
|
10% |
25% |
50% |
75% |
90% |
|
|
Ages by race |
|||||
|
White |
11.32 |
11.90 |
12.55 |
13.20 |
13.78 |
|
African American |
10.52 |
11.25 |
12.06 |
12.87 |
13.60 |
|
Hispanic American |
10.81 |
11.49 |
12.25 |
13.01 |
13.69 |
|
Overall median age |
11.11 |
11.73 |
12.43 |
13.13 |
13.75 |
|
SOURCE: Adapted with permission from "Age at Menarche and Racial Comparisons in U. S. Girls" W. Chumlea et al., Pediatrics, Vol. 111, pp.110-113, Copyright 2003. |
In boys the prostate gland and seminal vesicles increase noticeably in size during puberty. Although boys can experience orgasms throughout childhood, ejaculation is not possible until the prostate and seminal vesicles begin functioning under the influence of increasing testosterone levels. Typically, the first ejaculation occurs a year after the growth spurt has begun, usually around age 13, but as with menstruation, the timing is highly variable (Janssen, 2007). The initial appearance of sperm in the ejaculate typically occurs at about age 14 (Wheeler, 1991). There appears to be a period of early adolescent infertility in many girls and boys following initial menstruation or ejaculation. However, this should not be depended on for birth control. In some males sperm production occurs in the early stages of puberty, and even the first ejaculation can contain viable sperm.
Voice changes caused by growth of the voice box (larynx) occur in both sexes, but they are more dramatic in boys, who often experience an awkward time when their voice alternates between low and high pitches. Facial hair in boys and axillary (underarm) hair in both sexes usually appear approximately 2 years after pubic hair does. Increased activity of oil-secreting glands in the skin can cause facial blemishes, or acne.
Many of these physical developments are sources of concern or pride to the adolescent and his or her family and friends. Feeling self-conscious is a common reaction, and individuals who mature early or late often feel particularly self-conscious. Recent research indicates that early maturing girls experience significantly higher levels of social anxiety than girls who mature within a normative time frame (Blumenthal et al., 2011).
Social changes also take place. Boy-girl friendships often change, and adolescents are likely to become—at least temporarily—more homosocial, relating socially primarily with members of the same sex. This phase does not last very long, however. The period of adolescence is marked not only by physical changes but also by important behavioral changes. In the following pages, we look at some important areas of adolescent sexual behavior.