Sexual Development Differentiation Sex and Gender Sex genetic sex chromosomes anatomical sex internal and external genitalia sexual identity one s identity as male or female Gender social meaning attached to being male or female gender identity sense of being male or female gender role expectations about how a male or female should behave Androgyny hermaphrodism sex possessing both male and female reproductive organs gender possessing both male and female qualities Normal Prenatal Development Genetics Chromosomes each human cell contains 46 chromosomes occurring in pairs 23 pairs of chromosomes 22 autosomes determines e g hair color 23rd pair are the sex chromosomes male XY female XX Normal Prenatal Development Genetics Normal Prenatal Development Genetics Germ cells male sperm contains X or Y female ovum contains an X Y chromosome contains less genetic material than X chromosome Normal Prenatal Development Genetics Mother Father XX XY X X X Y XX female XY male XX female XY male Normal Prenatal Development Internal External Genitalia Undifferentiated stage 0 7 weeks gestation male and female external genitals the same urogenital fold genital groove genital tubercle labioscrotal swelling male and female internal genitalia the same undifferentiated sex glands Sexual differentiation Gonadal development 8 weeks gestation Y chromosome synthesis of H Y antigen Male H Y antigen causes undifferentiated sex glands to develop into testes Female lack of H Y antigen causes undifferentiated sex glands to develop into ovaries Sexual differentiation Duct development both sexes start out with two systems Mullerian ducts will develop into fallopian tubes uterus inner vagina Wolffian ducts will develop into epididymis vas deferens and seminal vesicles Male XY Testes secrete testosterone and Mullerian inhibiting hormone testosterone Wolffian ducts begin to develop Mullerian inhibiting hormone inhibits further development of Mullerian ducts they shrink and degenerate Female XX absense of Mullerian inhibiting hormone Mullerian ducts develop absense of testosterone Wolffian ducts degenerate Sexual differentiation Genital development Male XY testosterone causes unisex genitalia to develop into penis and scrotum testosterone converted to dihydrotestosterone dihydrotestosterone causes the external appearance of scrotum and penis Female XX absence of testosterone causes unisex genitalia to develop into clitoris labia vaginal opening etc NOTE The default is to develop as a female Male hormones are needed to promote differentiation into a male Normal Prenatal Development The Brain Sexual differentiation Male Testosterone secreted into the blood reaches the brain testosterone converted to estradiol and dihydrotestosterone in the brain estradiol masculinizes the brain Female alpha fetoprotein binds to estradiol prevents estradiol from entering the brain protects female brains from being masculinized by estradiol Prenatal hormone exposure fundamentally organizes the brain Sexual Reproductive Behaviors development of the hypothalamus sexual orientation Problem Solving Aggression Rough and tumble play Hormone exposure seems to involve a critical period exposure outside the critical period does not have the same impact on brain organization Brain Development Sex Differences Given different selection or evolutionary pressures on men and women how would you expect men and women to differ with regard to intellectual skills In other words in which areas would men demonstrate superior skill on average and in which areas would women demonstrate superior skill on average Men spatial rotation tasks mathematical reasoning tasks navigation through a route guiding or intercepting projectiles Women perceptual speed rapidly identifying matching items mathematical calculation tasks greater verbal fluency recalling landmarks from a route faster at precision manual tasks How meaningful are these sex differences What is the effect size Does a large effect size indicate that you are unlikely to find a woman who is better than a man at spatial rotation A man that is more verbally fluent than a women Do sex differences in skills arise from evolutionary pressures or cultural pressures In other words are the data consistent with an evolutionary interpretation or a cultural interpretation Both Neither Brain Development Sex Differences Animal studies Observational studies regarding spatial learning indicate female rats use landmarks pictures male rats use geometric cues angles in the absence of landmarks female rats use geometric cues male rats almost exclusively used geometric cues Brain Development Sex Differences Lutchmaya et al 2002 Obtained amniotic fluid from 87 pregnancies analyzed for fetal testosterone 40 girls 47 boys followed up at 18 and 24 months after birth Findings girls had significantly larger vocabulary fetal testosterone inversely correlated with vocabulary size when both sexes examined together fetal testosterone not correlated with vocabulary size when sexes examined separately Shute et al 1983 91 male and female students administered spatial test battery measured androgen levels Findings curvilinear relationship between androgen levels and spatial abilities high androgen females better spatial abilities than low androgen females low androgen males better spatial abilities than high androgen males Gouchie Kimura 1991 46 females 42 males 18 31yrs measured spatial ability math ability perceptual speed verbal articulation and vocabulary measured salivary testosterone Finding men with lower T performed better on spatial and math tasks than higher T males women with high T performed better than low T females Consider these findings from an evolutionary perspective What might be the adaptive benefit of having high or low testosterone for males and females What do these findings suggest about androgyny Brain Development Sex Differences Menstrual cycle fluctuations Hampson 1990 45 19 39yr old females tested cognitive skills across the menstrual cycle Findings Estrogen levels high lower performance on spatial skills abstract reasoning higher performance on verbal articulation fine motor skills Estrogen levels low better performance on spatial skills abstract reasoning tasks Note Effect sizes small Seasonal fluctuations Kimura Hampson 1994 men experience seasonal fluctuations in androgens such that T is lowest in the spring seasonal fluctuations in androgens correlated with performance on cognitive tasks T levels lower in