Chapter Ten Sexual Behavior

The Nature and Nurture of Sex Following an accident during a routine circumcision, David Reimer was raised as a girl. © Royalty-free/CORBIS © Royalty-free/CORBIS Money reported David was developing as a “normal” girl At 14, he refused to continue living as a girl, and his parents told him about his medical history. David original name was Bruce Had surgery, and hormone treatment and lived as a man David married and adopted his wife’s children. Tragically, David took his own life in May 2004 So which is more important? How we are raised or our genetics

The Genetics of Sex 22 chromosomes the same, 23rd different XX or XY Mother gives X chorm, father gives either X or Y, which determines sex

Stages of Prenatal Development Stages of Differentiation Development of gonads. Development of internal organs. Development of external genitalia. (Secondary characteristics) Normally, first three processes proceed in a specific order to produce an unambiguous male or female. In the case of intersexes, elements of both male and female development occur in the same fetus. The fetus starts as being undifferentiated, neither male nor female The presence of hormones will be what makes the difference Stages of Differentiation Development of gonads (ovaries, testes, organs that produce gametes, sperm and eggs) (at 6-8 weeks) Development of internal organs (prostate, seminal vesicles, vas deferens; uterus, upper vagina, fallopian tubes) (at 9-12 weeks) Development of external genitalia. (penis, clitoris, labia, scrotum, lower vagina)(third month) Secondary characteristics (obviously not a prenatal stage, but added here because it leads to differentiation (body hair at genitals, underarms, face, gamete production, voice deepens, muscles and external genitalia develop, breasts) Normally, all three processes proceed congruently to produce an unambiguous male or female. In the case of intersexes, elements of both male and female development occur in the same fetus. Money estimates that as many as 4% of births may by intersexual Fausto-Sterling suggests that maleness and femaleness should be viewed on a continuum and that there should be at least five genders – i’ll tell you about these after we look at how development occurs so that you can understand what i’m talking about

Thomas Beatie, the transman who is five months pregnant and documenting his experience in The Advocate. Beatie is legally male and legally married to his wife. They’ve wanted children for years, but his wife had endometriosis and a subsequent hysterectomy. http://img84.imageshack.us/img84/2640/thomasbeatiewm7.jpg

1. The Development of Gonads Up to the 6th week following conception, both males and females have undifferentiated primordial gonads. At the 6th week, the sex-determining region of the Y chromosome (SRY) gene is expressed in males. The SRY gene encodes testis-determining factor, which turns the primordial gonads into testes. Alternate genes guide the development of the primordial gonads into ovaries in females.

2. The Differentiation of Internal Organs Fetuses contain both a male Wolffian system and a female Müllerian system. Secretion of testosterone and anti-Müllerian hormone by the testes develops male internal organs. In the absence of testosterone and anti-Müllerian hormone, female internal organs develop. Adult females retain nonfunctional remnants of the Wolffian system. Here is the undifferentiated gonad (purple) At the 6th week, the SRY gene makes testis-determining factor in males (top blue circle). which turns the primordial gonads into testes. Alternate genes guide the development of the primordial gonads into ovaries in females. At this point Fetuses contain both (internal sexual systems) a male Wolffian system (green) a female Müllerian system. (purple) Secretion of testosterone (develops Wolffian system into male organs) anti-Müllerian hormone (degenerates female Mullerian system) In the absence of testosterone and anti-Müllerian hormone, female internal organs develop. Adult females retain nonfunctional remnants of the Wolffian system. (external organs still look similar)

Normal development of the accessory sex organs Testosterone Two axes of differentiation here Male and female are not on one scale, instead More or less feminine, more or less masculine nelson3e-fig-03-06-0.jpg Mullerian inhibitory hormone

3. Development of External Genitalia No hormonal influences are necessary for the development of female external genitalia. Masculinization of external genitalia requires stimulation by 5-alpha-dihydrotestosterone from the testes. 5-alpha-dihydrotestosterone results when testosterone is acted on by the enzyme 5-alpha-reductase. (Bottom of previous diagram) No hormonal influences are necessary for the development of female external genitalia. Masculinization of external genitalia requires stimulation by 5-alpha-dihydrotestosterone from the testes. 5-alpha-dihydrotestosterone results when testosterone is acted on by the enzyme 5-alpha-reductase.

Androgen-Insensitivity Syndrome (AIS) A defective gene produces abnormal androgen receptors in an XY fetus. Tissues are “blind” to androgens, so the Wolffian system does not develop. Anti-Müllerian hormone prevents development of normal female internal organs. Outward appearance and gender identity is typically female. If during this second stage, androgen does not cause Wolffian system to develop in an XY person, (A defective gene produces abnormal androgen receptors in an XY fetus), Tissues are “blind” to androgens, So they fail to develop male internal organs, but still have anit-mullerian hormone, so also don’t develop female internal organs Later developmental stages in stage three and puberty cause female external organs Although genetically male, usually have strong female gender identities From Money, J., and Ehrhardt, A.A. Man & woman, boy & girl. Baltimore: Johns Hopkins University Press, 1972.

Congenital Adrenal Hyperplasia (CAH) Heritable condition in which the fetus’s adrenal glands release excess androgens. Males may mature early. Females may have ambiguous external genitalia. Females with CAH often describe selves as “tomboys,” and engage in more lesbian and bisexual behavior. Congenital Adrenal Hyperplasia (CAH) Heritable condition in which the fetus’s adrenal glands release excess androgens. Males may mature early. Females may have ambiguous external genitalia. From Kalat, James, and T. Norton, eds., Brains to behavior: some recent and classical contributions. New York: MSS Information Corp., 1973.

Five genders? Male Male Pseudohermaphrodites (merms) True hermaphrodite (herms) Female Pseudohermaphrodites (ferms) Female Fausto-Sterling suggests that maleness and femaleness should be viewed on a continuum And that there should be at least five genders Male – testes and male genitalia Male Pseudohermaphrodites (merms) – testes and some female genitalia True hermaphrodite (herms) – both male and female gonads (ovary and testis) Female Pseudohermaphrodites (ferms) – ovaries and some male genitalia Female – ovaries and female genitalia

Development at Puberty Genitals and secondary sex characteristics mature. Mean age at puberty is dropping. Puberty may be triggered by accumulated fat. The hypothalamus releases gonadotropin-releasing hormone (GnRH). The anterior pituitary releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Puberty Genitals and secondary sex characteristics mature. Mean age at puberty is dropping (from 16 to 12) Puberty may be triggered by accumulated fat, which American girls have in plenty, (or early development from estrogen-like compounds in soap, plastic) The hypothalamus releases gonadotropin-releasing hormone (GnRH). (stimulates release of next two hormones in ant pit) The anterior pituitary releases follicle-stimulating hormone (FSH) luteinizing hormone (LH) Both hormones cause increased production of testosterone and estradiol (in different percentages) in males and females And development of secondary sex characteristics and gametes

Puberty in Males FSH and LH promote increased release of testosterone by the testes. Testosterone promotes development of male secondary sex characteristics: Muscular development Maturity of external genitalia Facial hair Enlargement of the larynx (deepening the voice) Regulation of sperm production (along with FSH and LH)

Puberty in Females FSH and LH stimulate estradiol production by the ovaries. Estradiol leads to female secondary sex characteristics: Breast development Maturity of external genitalia Maturity of the uterus Changes in quantity and distribution of fat In both males and females, estradiol slows skeletal growth

Sex Hormones Synthesized from cholesterol. Classified as steroids. Males and females both produce androgens and estrogens. Females produce about 10% of the amount of androgens produced by males.

The Human Menstrual Cycle 4 1 3 8 7 Couple of things to look at here: Levels of FSH and LH in blood Levels of estrogens and progesterones in blood Development of egg in ovary Lining in uterus 1. Day 1 of menstruation: anterior pituitary increases release of FSH. 2. FSH stimulates follicles (with egg inside), one follicle develops faster, and provides feedback to the hypothalamus and pituitary, which. 3. Follicle starts releasing estrogen 4. LH release is sharply increased. 5. Causes egg to release, Ovulation occurs at about day 14 (egg floats down fallopian tube) 6. Ruptured follicle becomes corpus luteum. 7. Corpus luteum releases estradiol and progesterone, thickening the uterine wall in preparation for the implantation of an embryo. 8. if fertilization does not occur, the corpus luteum stops producing estradiol and progesterone. 9. The uterus sheds its lining and the cycle repeats. How birth control pills work: 1. 6 5 2 9

Some Structures Are Sexually Dimorphic Rats SDN-POA and the SNB Humans INAH-3, hypothalamus, anterior commissure and thalamus Actually difficult to find gross brain differences b/t males and females What do these areas do? Sexually-dimorphic nucleus of the preoptic area (SDN-POA) – we don’t really know, altho lesions decrease male sexual behavior Area starts out same size in males and females when first born After a few days, androgens make SDN-POA grow Interstitial nucleu if the anterior hypothalamus (INAH) humans

Example of a sexually dimorphic anatomical difference: MOPA in rats Example of a sexually dimorphic anatomical difference: Females: more synapses on spines Males: more synapses on shaft We can’t connect this to a specific behavior, what does it do? Axon

Masculinization of the Nervous System Aromatization Changing of testosterone to estradiol Responsible for masculinizing the developing brain. In humans and many other mammals, the placenta normally blocks the mother’s estrogens, so females do not get masculinized; males make their own testosterone. Prenatal exposure to synthetic estrogens may masculinize the female brain (ex. CAH). Hyena females are both physically and behaviorly like male hyenas (penis, more aggressive) The hyena placenta does not prevent masculinization. Courtesy Dr. Stephen Glickman

Hormones and Sexual Orientation Early exposure to androgens may affect adult behavior in rats. Low-testosterone rats are more likely to engage in sexual activity with males. Unusual exposure to testosterone in females may promote sexual activity with females. Exposure to testosterone necessary for sexual dimorphism of SDN-POA in rats.

Hormones and Human Sexual Orientation Women exposed to high levels of prenatal androgens are more likely to engage in bisexual and lesbian behavior. But…most women exposed to high prenatal androgens are heterosexual. The vast majority of lesbians and bisexual women have not experienced exposure to high prenatal androgens.

Brain Structure and Sexual Orientation Courtesy Simon LeVay, Salk Institute Simon LeVay compared INAH-3 in heterosexual and homosexual males.

Other Correlations between Brain Structure and Sexual Orientation SDN-POA in rams that mate with other rams is about the same size of SDN-POA in ewes, and is different from rams that mate with ewes. The anterior commissure varies in size between homosexual and heterosexual male humans.

Genes and Sexual Orientation The likelihood of a gay man having a gay brother is: 25% for fraternal twins. 50% for identical twins. Data for lesbians are less clear, leading LeVay and others to question a genetic role in female homosexuality.

Hormones and Female Cognition Female performance on spatial tasks is best when testosterone levels are high and worst when estrogen levels are high. Verbal fluency and manual dexterity are correlated with high estrogen levels in women. Sex hormones also influcence how the brain circuits are formed

Androgens and Male Cognitive Behavior Males have a slight advantage over females in spatial tasks. Older men receiving testosterone supplements improved their performance on spatial tasks.

Seasonal Testosterone Levels

Spatial Ability at Different Times of the Year

Average sex differences in behavior often reflect significant overlap between the sexes nelson3e-fig-04-17-0.jpg

Parental Behavior Males Females promiscuity (being less selective) is balanced by the need to protect offspring. Females likely to be selective in their sexual partners because of high cost of reproduction

Hormonal Influences on Mating and Parental Behavior Monogamy and nurturing in voles may result from levels of vasopressin and oxytocin. Prairie voles are monogamous and nurturant. Montane voles are promiscuous and not nurturant. Oxytocin is released during human orgasm and when a mother is nursing her infant. Oxytocin – uterine contractions, milk let-down, increase maternal behavior Vasopressin – regulates body fluids (also called antidirectic hormone, ADH – tells kidneys to stop making urine) increase paternal behavior Receptors for both hormones in different places for different voles

More Biological Influences on Parenting Inhibiting progesterone activity in male mice increases nurturing behaviors. Mice lacking PEG3 genes do not nurture offspring.