1.1.2 THE SECONDARY SEXUAL CHARACTERISTICS
The secondary sexual characteristics begin to appear during puberty as a result of hormonal stimulation. They become apparent first in females, a little later in males. By the time their physical growth is completed, the bodies of men and women show several marked differences. (See also "The Role of Hormones.")
The following paragraphs summarize the physical changes of puberty. These changes may occur very slowly and extend over a period of more than a decade, or they may appear rather suddenly and be completed within one or two years. While general social conditions, diet, and climate may affect the development, much of it is also determined by heredity. For example, Asian men usually remain less muscular and develop less facial and body hair than European men.
In the male, the first body changes of puberty are the growth of the testicles, the appearance of pubic hair at the base of the penis, and an enlargement of the penis. These changes indicate that the body is reaching sexual maturity, and sometime thereafter the first ejaculation can occur. However, at first the ejaculate may not contain any sperm cells, but consist mainly of fluid from the prostate gland. (The first ejaculation may occur during masturbation or spontaneously while the boy is asleep. In the latter case, he is said to have a "wet dream.")
During puberty, the body grows rapidly in size. The shoulders become wider than the hips, the chest enlarges in every dimension, and the muscles in the arms, legs, and shoulders grow stronger and more obvious. The pubic hair becomes more dense and rather kinky, gradually forming a triangle that points upward toward the navel. Some hair also develops in the armpits (called axillary hair) and, in some males, on the chest. Generally, the male is hairier than the female. Eventually, he also develops facial hair which will grow into a beard unless it is shaved off regularly. As the male sex organs grow in size, the larynx (voice box or "Adam's apple") also enlarges. As a result, men generally have a deeper voice than women.
BOY (AGE 5)
In childhood the male and female bodies are very similar. The main difference is found in the external sex organs i.e. in the primary sexual characteristics.
GIRL (AGE 7)
During puberty both males and females rapidly gain in height and develop their secondary sexual characteristics. In males, the body becomes more muscular, and the shoulders grow wider than the hips.
During puberty females develop their secondary sexual characteristics of which the breasts are the most obvious. At the same time, their hips grow wider than their shoulders. The young teenage girl shown here is just experiencing the first of these and other physica! changes.
In adult males the secondary sexual characteristics are fully developed. Most noticeable are the generally more angular and muscular body arid, in some males, the growth of hair on the chest.
In adult females the secondary sexual characteristics are fully developed. Most noticeable are the generally rounder and softer body and the breasts.
ASIAN ADULT MALE
Many Asian men are less muscular and have less facial and body hair then most European men.
AFRO-AMERICAN ADULT MALE!
In African or Afro-American men and women the head- and body-hair is usually coarser and more curly than in European men and women.
Females experience the physical changes of puberty in the following order: First, the breasts begin to enlarge. Then some straight and later kinky or curly hair appears on the vulva. This pubic hair forms a triangle pointing downward. Eventually, some hair will also appear in the armpits (railed axillary hair). During this time, the body grows in height, and the hips become wider than the shoulders. Fatty tissue in and around the breasts, shoulders, hips,
THE SECONDARY SEXUAL CHARACTERISTICS
The Male: On the average, taller and heavier than the female.
1. Head hair: may fall out with age. 2. Facial hair: grows throughout adult life.
3, Features: more pronounced, face longer, head (front to back) longer. 4. Neck: thicker, longer, larynx one-third larger. 5. Shoulders: broader, squarer. 6. Chest: larger in every dimension. 7. Body hair: more evident, especially on chest and arms. 8. Breasts: rudimentary in size. 9. Muscles: bigger, more obvious. 10. Arms: longer, thicker, "carrying angle" straight. 11. Pubic hair: growing up to a point, forming triangle. 12. Hips: narrower. 13. Hands and feet: larger, fingers and toes stronger and blunter. 14. Thighs: more cylindrical with bulge of muscles. 15. Legs: longer, bulging calves. 16. Angle of thigh and leg; as with "carrying angle" of arm, forming straight line, thigh to ankle.
The Female: On the average, shorter and lighter than the male.
1. Head hair: more lasting. 2. Facial hair: very faint, usually noticeable only in later years, 3. Features: more delicate, face rounder, head smaller, rounder (from top). 4. Neck: shorter, more rounded, larynx smaller. 5. Shoulders: more rounded, sloping. 6. Chest: smaller, narrower. 7. Body Hair: very light and faint. 8. Breasts: prominent, also well-developed nipples with large surrounding rings, 9. Muscles: largely hidden under layers of fat. 10. Arms: "carrying angle" bent. 11. Pubic hair: forming straight line across at top. 12. Hips: wider, more rounded. 13. Hands and feet: smaller and narrower. 14. Thighs: wider at top and shorter in length, 15. Legs: shorter with smoother contours. 16. Angle of thigh and leg; as with "carrying angle" of arm, slightly bent, forming an ang!e at the knee. .
and buttocks gives the female body its generally rounder appearance. The first menstruation (also known as menarche) indicates approaching sexual maturity. In the beginning, the menstrual cycles are still irregular, and in some of them there may be no ovulation. In other words, for a while a girl may menstruate and still be largely infertile. Indeed, a woman usually gains her full reproductive capacity only one or two years after her first menstruation.
In females, there is no decisive enlargement of the larynx and therefore no voice change comparable to the one taking place in males. In general, women are also less muscular and slightly shorter than men.
At the end of puberty, the breasts have developed their typica! rounded shape and thus become the most obvious female secondary sexual characteristic. However, they do not produce milk until after pregnancy. (See "Birth.")