istic act of risking one’s life to warn or aid another.
Because many of these behaviors are found in a vari-
ety of other animal species, and some appear early in
human infancy, their source is believed to be at least
partly genetic. Additional sources of influence are
suggested by the hundreds of studies that reveal age-
related increases in the production of human proso-
cial acts that parallel increases in moral reasoning,
the ability to see the perspective of others, and expe-
riencing and showing emotional concern. Adults and
peers can also increase the degree of a child’s proso-
cial behavior by modeling and labeling it, discussing,
and rewarding it when it appears in the child’s ac-
tions. Differences in temperament, personal experi-
ences, cultural expectations, and the nature of the
situation also influence children’ prosocial behavior.
See also: ALTRUISM; SOCIAL DEVELOPMENT
Bibliography
Berk, Laura. Child Development, 5th edition. Boston: Allyn and
Bacon, 2000.
Eisenberg, Nancy, and Richard Fabes. ‘‘Prosocial Development.’’
In Handbook of Child Psychology, Vol. 3: Social, Emotional, and
Personality Development, 5th edition, edited by William Damon.
New York: John Wiley and Sons, 1998.
Honig, Alice, and D. S. Wittmer. ‘‘Helping Children Become More
Prosocial: Ideas for Classrooms, Families, Schools, and Com-
munities.’’ Young Children 51 (1996):62–70.
Vasta, Ross, Marshall Haith, and Scott Miller. Child Psychology: The
Modern Science, 3rd edition. New York: John Wiley and Sons,
1999.
Edward J. Forbes III
PUBERTY
Puberty is the time of life in which physical and hor-
monal changes take place in the body making it capa-
ble of reproduction. It occurs primarily during early
adolescence. Changes can begin as early as age nine
or as late as age seventeen. Nutrition, health, and ge-
netic factors determine when a child starts puberty.
Girls usually start puberty earlier than boys. First
changes are internal; external changes are noticeable
in the development of breasts and appearance of
pubic hair. The sequence of changes for girls are as
follows:- Ovaries increase production of estrogen
- Internal sex organs begin to grow larger
- Breast bud stage
- Pubic hair begins to appear
- Weight spurt begins
- Peak height spurt
- Peak muscle and organ growth (also, hips be-
come wider) - Menarche (first menstruation)
- First ovulation
- Final pubic hair pattern
- Full breast growth
Boys’ changes are also initially internal. The first
external signs are growth of the scrotum and appear-
ance of pubic hair. The sequence of changes for boys
are as follows: - Testes increase production of testosterone and
progesterone - Testes and scrotum grow larger
- Pubic hair begins to appear
- Penis growth begins
- First ejaculation
- Weight spurt begins
- Peak height spurt
- Peak muscle and organ growth (also, shoulders
become broader) - Voice lowers
- Facial hair appears
- Final pubic hair pattern
See also: ADOLESCENCE; MATURATION; MENARCHE
Bibliography
Bell, Ruth. Changing Bodies, Changing Lives, 3rd edition. New York:
Random House, 1998.
Harris, Robie H. It’s Perfectly Normal. Cambridge, MA: Candlewick
Press, 1994.
Jane L. Abraham
PUBERTY 337