1. Chapter 10 Reproductive Behaviors
Module 10.1:
Sex and Hormones
Module 10.2:
Variations in Sexual
Behavior

2. Sexuality
Gender identity: how we identify sexually and what we call ourselves
Sex differences: Biological differences between males and females
Gender role: refers to the activities and dispositions that a particular society encourages for one sex or the other

3. Jazz is a transgender child. See her story at:
Gender Identity
Most people have a gender identity that matches their external appearance.
Some people have a gender identity that is opposite their biological sex.
Jazz is a transgender child. See her story at:

4. Psychologists and researchers once believed that gender identity was learned and more a product of rearing and experience.
Current evidence strongly suggests that biological factors, especially prenatal hormones, play a large role in gender identity.

6. Variations in Sexual Development
True hermaphrodite: someone who has both testicular and ovarian tissue—very rare
Hermaphrodites: individuals whose genitals do not match the normal development for their genetic sex
Intersex people are people are intermediate between being male or female (AKA: pseudohermaphrodite)

7. Video: Is It a Boy or a Girl? (1999)
Part One:
Part Two:
Part Three:

8. Sex Hormone Endocrine glands
A chemical that is secreted by a gland, conveyed by the blood, and affects other organs
Glands that produce hormones

9. Sex Hormones Two types of sex hormones: Androgens Estrogens
Both sexes have both hormones

10. Sex and Hormones
Androgens are a groups of male sex hormones that include testosterone
Generally referred to as “male hormones” because men have higher levels than women

11. Sex and Hormones
Estrogens include estradiol and others and are referred to as “female hormones” because women have higher levels.
Progesterone is a type of hormone that prepares the uterus for the implantation of a fertilized ovum and promotes the maintenance of pregnancy.

12. Sexual Differentiation
Begins with the chromosomes
At six weeks of development, both sexes have primitive gonads as well as:
Mullerian ducts (precursors to female reproductive organs) and
Wolffian ducts (precursors to male reproductive organs).

13. Sexual Differentiation
The male Y chromosome includes the SRY gene which causes the primitive gonads to develop into testes, the sperm-producing organ.

14. Sexual Differentiation
The developed testes produce the hormone testosterone.
Testosterone induces the development of the penis and scrotum.
Females are not exposed to high testosterone levels and their gonads develop into ovaries, the egg-producing organs.

15. Sex and Hormones
Sensitive periods are early periods when hormones have long-lasting effects.
Sexual differentiation depends mostly on the level of testosterone during a sensitive period.
The human sensitive period for genital formation is about the third and fourth month of pregnancy.

16. Sex and Hormones Sex hormones can have the following effects:
Organizing effects- occur mostly at sensitive stages of development.
-Determine whether the brain and body will develop male or female characteristics
Activating effects- occur at any time of life and temporarily activate a particular response.

17. Congenital adrenal hyperplasia (CAH)
XX female’s cortisol production leads to overstimulation of the adrenal gland.
Overstimulation of the adrenal gland leads to extra testosterone production.
The female fetus becomes partly masculinized.

18. Congenital adrenal hyperplasia (CAH)
Research indicates that CAH girls show a greater preference for boy-typical toys than do other girls.
During adolescence and early adulthood, they also show partly masculinized interests.
Sexual interest and activity also differs for CAH girls as well.

19. Androgen insensitivity or testicular feminization
XY male has the genital appearance of a female.
Production of androgens remains normal but they lack the androgen receptor that enables it to activate genes in a cell’s nucleus.
Condition occurs in various degrees from a smaller than average penis to genitals that develop a female appearance.
Four siblings with testicular feminization syndrome (recessive sex-linked gene)

20. 5 alpha-reductase 2 deficiency
XY males fail to produce an enzyme that converts testosterone to dihydrotestosterone.
Most look female at birth but a penis develops during adolescence and puberty.
Most then accept a male gender identity.
Brain is exposed to testosterone during early development.

21. Biological Bases of Sexual Orientation
Organizing effects of sex hormones
Sexually dimorphic nucleus (SDN): an area in the anterior hypothalamus that is larger in the male and contributes to control of male sexual behavior, (e.g., being attracted to a female).
Study of homosexual male brains found that their SDN was similar to those found in females.

22. Biological Bases of Sexual Orientation
Twin studies suggest genetic factors.
Probability is highest in monozygotic twins and lower in dizygotic twins, and even lower in siblings and adopted brothers or sisters.
Because monozygotic twins can have opposite sexual orientations, genes are not the only factor.

23. Biological Bases of Sexual Orientation
Sexual orientation may be influenced by testosterone levels during sensitive periods of brain development.
Male animals deprived of testosterone early in life show sexual interest in other males as adults.
Female animals exposed to testosterone during early development show an increased likelihood of mounting behavior.

24. Biological Bases of Sexual Orientation
Laboratory research has also shown that prenatal stress can alter sexual development.
Male subjects subjected to either prenatal stress or alcohol developed male sexual behavior in addition to female sexual behaviors.
Male subjects exposed to both stress and alcohol during prenatal development had decreased sexual behavior.

25. Biological Bases of Sexual Orientation
The probability of homosexual orientation is higher among men with older brothers.
Research suggests that a mother’s immune system may react against a protein in a son and attacks subsequent sons to alter development.