10/21 Lecture #14: Sex How do you define a ?male? and a ?female?? Size of the gametes Larger gametes are females, smaller gametes are male Hormones and behavior Sex differences: the body Sex differences: early organization f behavior People: variation Hormones in adulthood Gonads Primordial gonad (all start with same gonad) Becomes either testis or ovary SRYtestis different hormone secretion Hormones and the internal sex organs Start as 2 distinct sets of structures Mullerian ducts (female) Wolffian ducts (males) Then from the testes: Mullerian inhibiting factorone set dies (mullerian ducts) Testosterone (T)one set develops (wolffian ducts) (T alters gene expression) External genitalia Initially undifferentiated In males: Testes secrete testosterone testosterone causes: Fusion of folds Enlargement of genital tubercle In females: The absence of T permits the development of the clitoris and labia Females are the default sex (no testosteronefemale) Exception: Psueduopenis in a female spotted hyena Sex structure similar to male sex structure Doest early testosterone influence development of behavior and the brain as it does the genitalia? When provided T in adulthood, female rates did not exhibit more male like behavior but males do When provided with estradiol and progesterone (E and P) in adulthood, adult males don?t show more female like behavior but females do Why? The organizational hypothesis: males are exposed to T early in life and that promotes the development of a male bran in and inhibit the development of a female one tested in 1959 by Phoenix Goy Gerall and Young gonads removed in all subjects Conclusion: the prenatal period is a time when fetal hormones have an organizing action on neural tissues mediating behavior. During adulthood the hormones are activational Organizational effects of Testosterone many behaviors dispersal, ranging, fighting, taste preferences,, courtship, sexual preference, copulating, spatial memory many species dogs, rats, cats, ferrets, monkeys, hamsters, humans? some effects depend on aromatization some sex difference don?t depend on testosterone birdsong Organizational effects of testosterone on the brain: the SDN: sexually dimorphic nucleus of the hypothalamus five times larger in a male than a female and much more in many species many sex difference in the human nervous system Variation Example E1: androgen insensitivity syndrome xy testes don?t descent but do secrete T Internal sex organs? External genitalia? Some raised as boys, most as girls Behavior? Indistinguishable from control female Not homosexual, female gender identity, liked dolls, fantasize about family Not able to reproduce Example #2: 5-alpha-reductase deficiency The ?guava doce? Boys look like girls Raised as girls until puberty Missing an enzyme that makes 5-alpha DHT from testosterone for external genital At puberty, they grow a penis The Guevedoces rech puberty T rises dramatically Everything changes Behavior? Imperator McGinley 1979: woman in Dominican Republic 17/18 switched gender identity to males 16 became heterosexual males 15 living with or married to women ?middle sex? Interpretations: Imperato McGinley 1979: The extent of androgen exposure of the brain in utero and at puberty has more effect on male gender identity than does sex of rearing Does this conclusion make sense? Cane we learn anything from them? Were Freud and other wrong about the age at which gender identity is firmly established? Cases in Brazil and Turkey were the same, Sicilians complicate the story Example #3: Congenital adrenal hyperplasia The adrenal produces heaps of testosterone before birth The genitals? At birth the adrenal problem is taken care of Did the exposure to T masculine or defiminize the behavior of the girls? CAH females: Differ from control Call themselves tomboys No interest in dolls Little interest in infants Prefer career to marriage No Wedding fantasies Similar to control: Aggressive behavior Actual marriage rates (1968) More recent studies: Postures Toy preferences What do CAH individuals tell us about sex differentiation in humans? Doe sit mean that like rats, a man?s behavior is masculinized and defiminized by early organizational effects of T?
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