Sex and Gender Differences

1. Sex and Gender Differences

2. 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

3. Figure 4.1 Human chromosomes

4. 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

5. Figure 4.2 Development of the male and female reproductive tracts

6. 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

7. Figure 4.3 Development of the male and female external genitalia (Part 1)

8. Figure 4.3 Development of the male and female external genitalia (Part 2)

9. Figure 4.3 Development of the male and female external genitalia (Part 3)

10. Figure 4.4 Descent of the testicles (Part 1)

11. Figure 4.4 Descent of the testicles (Part 2)

12. 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

13. 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)

14. Figure 4.6 Partial masculinization of genitalia in a girl with congenital adrenal hyperplasia

15. Box 4.1 Personal Points of View: My Life With Androgen Insensitivity Syndrome

16. 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

17. Figure 4.7 Mental rotation task

18. Figure 4.8A Test of object location memory

19. Figure 4.8B Test of object location memory

20. 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

21. Figure 4.9 Gender constancy

22. Figure 4.10 Toy preference test

23. 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

24. Figure 4.11 Monkeys show humanlike toy preferences

25. 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

26. Box 4.2 Biology of Sex: “Eggs at Twelve”

27. Box 4.3 Personal Points of View: The Boy Who Was Raised as a Girl

28. Figure 4.12 Hormones and play

29. Figure 4.13 Finger-length ratio and gender

30. 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

31. Figure 4.14 Babies enter a gendered world

32. Figure 4.15 Influence of siblings on gender

33. Figure 4.16 The media influence gender

34. Figure 4.17 Influence of gender stereotypes on children’s memories

35. 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

36. 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

37. Figure 4.19 Chastity Bono transitioned to Chaz Bono in 2009

38. Figure 4.20 The vulva after sex-reassignment surgery

39. Figure 4.21 Transformation of the clitoris into a small penis

40. Box 4.5 Controversies: How Should We Treat Gender-Dysphoric Children?

41. Figure 4.22 Kate Bornstein