Sex and Gender Differences

Genes and Hormones Guide Sex Development Testes and ovaries form from the precursor gonads The gene that instructs the ridges to differentiate into testes is called SRY This gene is located on the Y chromosome

Figure 4.1 Human chromosomes DHS2e-Fig-04-01-0.jpg

Male and Female Reproductive Tracts Develop from Different Precursors Embryos of both sexes possess both Wolffian and Müllerian ducts Wolffian ducts are precursors of the male reproductive tract Müllerian ducts are precursors of the female reproductive tract In males, testes produce anti-Müllerian hormone (AMH) to eliminate the female ducts In females, the absence of AMH allows Müllerian ducts to persist and to develop into the oviducts, uterus, and deeper parts of the vagina

Figure 4.2 Development of the male and female reproductive tracts DHS2e-Fig-04-02-0R.jpg

Male and Female External Genitalia Develop from the Same Precursors Female and male external genitalia have the same developmental origin Most prenatal sex development occurs during weeks 8 through 24 of gestation, when testosterone levels are high in male fetuses The testicles descend during development

Figure 4.3 Development of the male and female external genitalia (Part 1) DHS2e-Fig-04-03-1R.jpg

Figure 4.3 Development of the male and female external genitalia (Part 2) DHS2e-Fig-04-03-2R.jpg

Figure 4.3 Development of the male and female external genitalia (Part 3) DHS2e-Fig-04-03-3R.jpg

Figure 4.4 Descent of the testicles (Part 1) DHS2e-Fig-04-04-1R.jpg

Figure 4.4 Descent of the testicles (Part 2) DHS2e-Fig-04-04-2R.jpg

The Brain Also Differentiates Sexually There are differences in brain structure, function, and chemistry between the two sexes These differences are brought about by higher levels of androgens in males than in females during development

Sex Development May Go Awry Chromosomal anomalies that do not fall under typical female (46,XX) or male (46,XY) chromosomal complements affect growth and fertility Klinefelter syndrome (XXY, XXXY) Turner syndrome (XO) XYY syndrome Triple-X syndrome The gonads or genitals may be sexually ambiguous Gonadal intersexuality Congenital adrenal hyperplasia (CAH) Androgen Insensitivity Syndrome (AIS)

Figure 4.6 Partial masculinization of genitalia in a girl with congenital adrenal hyperplasia DHS2e-Fig-04-06-0.jpg

Box 4.1 Personal Points of View: My Life With Androgen Insensitivity Syndrome DHS2e-Box-04-01-0.jpg

Gender Is a Central Aspect of Personhood Gender identity is the sense of which sex one belongs to. For some people, gender identity does not match anatomical sex This identity is expressed via gender role behavior Sexual orientation, cognition, and personality traits differ between men and women Differences in sexuality include attitudes toward casual sex, jealousy, and frequency of masturbation

Figure 4.7 Mental rotation task DHS2e-Fig-04-07-0.jpg

Figure 4.8A Test of object location memory DHS2e-Fig-04-08A-0.jpg

Figure 4.8B Test of object location memory DHS2e-Fig-04-08B-0.jpg

Gender Is a Central Aspect of Personhood Many gender differences arise at a young age By about 3 years of age, most children show evidence of gender constancy By about 1 year of age, most children can distinguish between men and women Differences in toy preferences

Figure 4.9 Gender constancy DHS2e-Fig-04-09-0.jpg

Figure 4.10 Toy preference test DHS2e-Fig-04-10-0.jpg

Biological Factors Influence Gender Evolutionary factors influence gender development Evolutionary factors: Cognitive differences between the sexes due to long-standing division of labor between men and women Difference in interest in casual sex between men and women Jealousy

Figure 4.11 Monkeys show humanlike toy preferences DHS2e-Fig-04-11-0.jpg

Experiments Demonstrate a Role for Sex Hormones Girls with CAH have behavioral traits shifted in the masculine direction Prenatal androgens influence gender The 2D:4D ratio correlates with many gendered characteristics

Box 4.2 Biology of Sex: “Eggs at Twelve” DHS2e-Box-04-02-0.jpg

Box 4.3 Personal Points of View: The Boy Who Was Raised as a Girl DHS2e-Box-04-03-0.jpg

Figure 4.12 Hormones and play DHS2e-Fig-04-12-0.jpg

Figure 4.13 Finger-length ratio and gender DHS2e-Fig-04-13-0.jpg

Life Experiences Influence Gender Life experiences influence gender development beginning early in life Observing socialization Rewards and punishments Imitation Cognitive models focus on thought processes Gender schemas Sexual scripts

Figure 4.14 Babies enter a gendered world DHS2e-Fig-04-14-0.jpg

Figure 4.15 Influence of siblings on gender DHS2e-Fig-04-15-0.jpg

Figure 4.16 The media influence gender DHS2e-Fig-04-16-0.jpg

Figure 4.17 Influence of gender stereotypes on children’s memories DHS2e-Fig-04-17-0.jpg

Transgendered People Cross Society’s Deepest Divide Unhappiness caused by discordance between anatomical sex and gender identity is called gender dysphoria F-to-M transexuals (trans men) M-to-F transexuals (trans women) Transvestism Autogynephilia

Transgendered People Cross Society’s Deepest Divide Sex-reassignment is a multistage process Some transexuals do not desire surgery Some medical centers treat pre-pubertal children affected by gender dysphoria Transgenders and transexuals struggle for awareness and acceptance

Figure 4.19 Chastity Bono transitioned to Chaz Bono in 2009 DHS2e-Fig-04-19-0.jpg

Figure 4.20 The vulva after sex-reassignment surgery DHS2e-Fig-04-20-0.jpg

Figure 4.21 Transformation of the clitoris into a small penis DHS2e-Fig-04-21-0.jpg

Box 4.5 Controversies: How Should We Treat Gender-Dysphoric Children? DHS2e-Box-04-05-0.jpg

Figure 4.22 Kate Bornstein DHS2e-Fig-04-22-0.jpg