Psychology2016

Sexuality and Gender 393

fat deposits on the buttocks and thighs. Some secondary sex characteristics also involve
the growth and development of the primary sexual organs. In females, this occurs when
the mammary glands in the breasts become capable of producing milk for an infant and
when the menstrual cycle begins (Biro et al., 2013; Kreipe, 1992; Lee, 1995).

MALE SECONDARY SEX CHARACTERISTICS The secondary sex characteristics of males
include a deepening voice; emergence of facial, chest, and pubic hair; and the development
of coarser skin texture. These changes are also accompanied by a large increase in height
that continues beyond the growth spurt of the female. The male growth spurt occurs about
2 years later than the female growth spurt, but males continue to gain height until the late
teens. Although the larynx (voice box) increases in size in both sexes, it increases so much in
males that part of the tissue forming it becomes visible under the skin of the neck in a struc-
ture known as the Adam’s apple. Primary sex characteristics also undergo changes during
puberty, including the onset of the production of sperm (spermarche, occurring at a little over
14 years of age) and the growth of the penis and testes, which will eventually allow the male
to function sexually and to reproduce (Kreipe, 1992; Lee, 1995; Song et al., 2015).

The Development of Sex Characteristics

10.2 Explain how sex characteristics develop.

How does the person’s body know which sexual characteristics

to develop? Aren’t some babies born with sex organs belonging to

both sexes?

The primary sex characteristics develop as the embryo is growing in the womb as a result
of the chromosomes contained within the embryonic cells as well as hormonal influences.

mammary glands

glands within the breast tissue that

produce milk when a woman gives

birth to an infant.

Puberty changes come about 2 years earlier

for girls than for boys, including the growth

spurt. The young people in this dancing

couple are both 13 years old, but the

physical difference in height is quite obvious.

External genitalia

Clitoris

Vagina

Uterus

Ovary

Fallopian

tube

Mammary gland

Menstruation

Enlargement of uterus,

clitoris, labia

Pubic hair

Rounded

body

contours

Breast development

Underarm hair

Acne

Testis

Epididymis

Scrotum

Penis

Urethra

Vas deferens

Prostate gland

Seminal vesicle

Ejaculation

Enlargement of

scrotum, penis,

testes

Pubic hair

Underarm hair,

chest hair,

muscle development

Voice change

Beard

Acne

Figure 10.1 Male and Female Sexual Organs
These figures show the primary and secondary sexual characteristics of women and men. Primary sexual
characteristics develop during the prenatal period, while secondary characteristics develop during puberty.

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