Reproductive Behaviors PDF

11/7/24, 4:00 PM OneNote Reproductive Behaviours September 7, 2023 3:34 PM Chapter 10- Reproductive Behaviours Sex and Hormones Sexual differentiation begins with the chro...

11/7/24, 4:00 PM OneNote Reproductive Behaviours September 7, 2023 3:34 PM Chapter 10- Reproductive Behaviours Sex and Hormones Sexual differentiation begins with the chromosomes: Female = XX, Male = XY In early prenatal development, males and females start with the same anatomy --> both have Müllerian ducts (precursors to female internal structures - uterus, upper vagina) and Wolffian ducts (precursors to male internal structures - vas deferens and seminal vesicles), and undifferentiated gonads (that will become testes or ovaries) What differentiates these gonads? ○ The SRY Gene (sex-determining region) The Y chromosome includes the SRY gene (Sex-determining Region on the Y chromosome) Causes the primitive gonads to develop into testes, which produce androgens which: Increase testes growth Produce Müllerian-inhibiting hormone (MIH) Fs do not have the SRY gene and their gonads develop into ovaries (which do not produce MIH) "Default sex" is female ○ Differentiation of Human Genitals Hormones in Males and Females Androgens and estrogens are categories of chemicals (steroids, in fact!), not chemicals themselves: ○ Androgens: testosterone (most common) ○ Estrogens: estradiol (most common), progesterone Testes produce more androgens than estrogens. Ovaries produce more estrogens than androgens. The adrenal glands (above the kidneys) also produce both androgens and estrogens. Genes and Sex Differences Hormones do not explain all biological differences between males and females ○ Genes on the X and Y chromosomes also produce differences Organizing Effects and Activating Effects of Sex Hormones Organizing Effects: occur at sensitive periods of development  (i) before birth – sex hormones determine if M or F genitals develop (ii) at puberty – sex hormones produce breast development in Fs, facial hair in Ms ○ Some differences in brain anatomy between Ms and Fs also increase during puberty Activating Effects: occur at any time of life and temporarily activate a particular response  e.g., increase in sex drive, menstruation ○ Current hormone levels influence the degree of sex drive ○ The burst of hormones during pregnancy produces temporary effects on emotional arousal, defensive behaviours, and cognition. Sex differences in the hypothalamus Sex hormones early in life influence development in the hypothalamus and amygdala (and other brain areas) Sexually dimorphic nucleus ○ In the anterior (front) hypothalamus ○ Larger in Ms; involved in the control of male sexual behaviour ○ Parts of the F hypothalamus generate a cyclical pattern of hormone release (menstrual cycle) Sex Differences in Childhood Behaviour: Toy Preferences The second largest sex difference in behaviour (What’s #1?) ○ #1 is sexual preference after puberty Typically, boys play with cars, trains, and balls, and play roughly; girls play with dolls and tea sets, and play cooperatively (“play house”) Partly due to socialization, but also due to general preferences of each sex (find same result in monkeys not subject to any human socialization) Influenced by prenatal testosterone  girls exposed to too much testosterone before birth show male toy preferences Activating Effects of Sex Hormones At any time, sex hormones exert activating effects to temporarily modify behaviour (hormonal secretions can influence sexual behaviour within minutes) Behaviour can also influence hormone secretion  e.g., link between aggression and testosterone is bidirectional. Oxytocin Released by the pituitary gland; it is not a sex hormone, BUT it.. https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 1/6 11/7/24, 4:00 PM OneNote ○ Is important for reproductive behaviour ○ Stimulates uterine contractions during delivery ○ Stimulates mammary glands to release breast milk ○ Is released following orgasm ○ Has recently been linked to high levels of generosity, higher levels of trust, and lower levels of anxiety ○ Is responsible for “pair bonds” (dating partners, mother and infant)  the “cuddle hormone” Males Sexual arousal ○ Testosterone – necessary for M sexual arousal – binds to parts of the hypothalamus causing the release of dopamine (the more dopamine, the stronger the sex drive)  stimulating certain dopamine receptors facilitates an erection ○ Dopamine stimulates sexual activity, but serotonin inhibits it by blocking dopamine release  antidepressants (which increase serotonin) decrease sexual arousal Testosterone (T) levels ○ T levels correlate positively with sexual arousal and the drive to seek many sexual partners ○ Married males or those in a committed relationship generally have lower T levels than single males High T levels result in greater than average desire to seek additional sexual partners, even if in a committed relationship Single Fs have higher T levels than married Fs ○ There are substances in the environment that can inhibit the production or release the production of testosterone. A family of chemicals known as phthalates. These are banned from use for children, but are not banned from use with pregnant women. They're in cosmetic items such as hairspray, and cause less masculinization of the brain than there would be if there was no contact with phthalates. Phthalates show up in urine. Sexual Interest ○ Research on T levels and sexual interest show direct correlation (even in Fs) ○ Low T is not the usual reason for impotence --> usual cause is impaired blood circulation ○ Castration generally decreases sexual interest and activity T reduction (i.e., chemical castration) (MPA drug) done to control sex offenders  problem with adherence and negative side effects (depression, weight gain, osteoporosis, cardiovascular disease) Reversable drugs, but side effects may not be reversable ○ Orchiectomy (actual castration) Research on 157 Orchiectomized Norwegians (many were sex offenders) Leads to reduction in sexual interest and behaviour Rate and degree of reduction are variable  50% became asexual within two weeks of the operation, some lost ability to achieve an erection but experienced some sexual interest for a few months, and some continued to have sex (although less enthusiastically) for a few months Of the 100+ sex offenders, only 3 re-offended (so, effective treatment) BUT… why was sexual interest and activity evident in some castrated men? Adrenal androgens Females The Menstrual Cycle ○ The hypothalamus and pituitary gland interact with the ovaries to produce the menstrual cycle (the periodic variation in hormones and fertility over about 28 days) FSH (follicle-stimulating hormone) and LH (luteinizing hormone) ○ After the end of a menstrual period: Anterior pituitary releases follicle-stimulating hormone (FSH), which promotes growth of follicle (fluid-filled sac that contains an immature ovum) in the ovary Follicle nurtures the ovum and produces estrogen (estradiol) ○ Towards the middle of the menstrual cycle, the follicle builds up receptors to FSH As a result, the follicle produces increasing amounts of estradiol ○ Increased estradiol causes the anterior pituitary to increase release of FSH and luteinizing hormone (LH) ○ FSH and LH cause the follicle to release an ovum ○ Birth-control pills prevent the surge of FSH and LH ○ The remnants of the follicle release the hormone progesterone (I hate progesterone), which: Prepares the uterus for implantation of a fertilized ovum Inhibits further release of LH The Periovulatory Period ○ Days of the cycle when fertility is highest Middle of menstrual cycle ○ Fs become more sexually responsive: Greater interest in erotic videos Greater interest in flirting Are more attracted to more masculine-looking and masculine-acting men Parental behaviour (from textbook) Increased secretion of oxytocin and prolactin after birth of young help promote milk production and several aspects of maternal behaviour in the mother ○ Eats and drinks more, is more aggressive, etc. Hormone receptor patterns also change as female becomes more sensitive to estradiol. Pregnancy leads to decreased gray matter volume in several areas (pruning the most ineffective synapses)- brain change is adaptive Vasopressin = linked to sexual fidelity https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 2/6 11/7/24, 4:00 PM OneNote Rats that have never been mothers will eventually adapt to parenthood- showing that even without the hormones, they start to show maternal care, although not as quickly- experience dependant more than hormonal dependent Brain Differences: M and F Prenatal androgens and estrogens influence many aspects of brain development At least 85 genes more active in the brains of one sex than the other  but there are likely more Differences exist between Ms and Fs in size of certain brain areas and activity levels in certain areas (e.g., serotonin production is 52% higher in Ms than in Fs  may explain why Fs are more prone to depression) ○ Areas in pink are, on the average, larger in women relative to the total mass of the brain ○ Areas in blue are, on the average, larger in men relative to the total mass. Why is this important? ○ Because M/F brains differ, we may need to develop sex-specific treatments for depression, Parkinson’s, etc. E.g., we know SSRIs are more effective for F (because SSRIs’ effects are increased by estrogen) ○ Brain research needs to have Fs and males as participants, or else results may be relevant to only males or Fs. Differences in Brain Anatomy and Sex Differences A. Fs more likely to use both sides of the brain at the same time  band of neurons connecting the hemispheres (corpus callosum and the anterior commissure) is more dense – explains why Fs are better multi-taskers than males B. The F brain has a greater density of neurons in parts of the temporal lobe associated with language processing and comprehension  Fs outperform males on tests of verbal ability C. Young F’s brains mature faster in the frontal lobes which are responsible for language learning (and controlling aggressive and impulsive behaviour)  Fs learn language faster and are better able to control impulses D. Young M’s brains mature faster in areas responsible for spatial ability (parietal lobe)  males have better spatial ability Effects of Sex Hormones on Nonsexual Characteristics Sex hormone levels do NOT differ between boys and girls from six months of age to puberty  so, differences in childhood that are hormone-based are the result of hormone differences in utero or soon after birth ○ E.g., prenatal testosterone appears to trigger boys’ fidgetiness Ability to recognize facial expressions of emotion ○ Research: Fs receiving testosterone injections became less accurate at recognizing facial expressions of anger Increased testosterone decreased Fs’ ability to infer a person’s mood from watching their eyes Testosterone and Mood: ○ High levels in males linked to delinquency, rambunctiousness, moodiness, aloofness, and sadness ○ High levels (in males and Fs) linked to aggressive behaviour  but, is level important or is fluctuation more important? Fluctuations are much less significant in people with higher testosterone levels, because if you have a low level, there's more to go. As well, going up or down a lot would produce changes. ○ T less important as males age (levels decrease) **Behaviour affects T-levels as well  e.g., T levels increase after a man behaves aggressively Testosterone and Spatial Ability ○ In general, males > Fs on spatial tasks ○ Fs whose glands overproduce T have spatial abilities more like the average M’s ○ Males whose glands underproduce T have spatial abilities more like the average F’s ○ As males age, T levels decrease, and spatial ability decreases ○ When T is given to males to increase sex drive, spatial ability improves! Sexual Behaviour, Gender Identity, and Gender-Differentiated Behaviours People vary in frequency of sexual behaviour, preferred types of sexual activity, and sexual orientation Sex differences: Biological differences Gender Differences: Differences that results from people’s thoughts about themselves as M or F Gender identity: how we identify sexually and what we call ourselves (“M” or “F”)  most people have a gender identity that matches their physical appearance https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 3/6 11/7/24, 4:00 PM OneNote Chromosome patterns that are neither XX nor XY (from textbook) Turner syndrome: characterized by an XO pattern- an X chromosome and no second sex chromosome, or just part of a second X chromosome, or one X in some cells and 2 Xs in others. The result is a typical feminine appearance/identity, but ovaries that secrete less than average amounts of sex hormones. ○ Difficulty getting pregnant, below average math and visuospatial skills, normal or above average performance on certain aspects of language. ○ Social difficulties and depression are somewhat more common Klinefelter syndrome: characterized by an XXY pattern, or less commonly XXYY or XXXY. Appearance is masculine, but usually infertile. ○ Smaller testes than average, some breast growth is common at puberty, learning difficulties especially with language and problem solving are common, and mental health problems are elevated. ○ Extra Y chromosome correlates with taller height and increased probability of cognitive impairment- no increased aggression. Intersexes (Hermaphrodites) Have anatomies intermediate between male and female (or a mixture)  have testicular AND ovarian tissue Genitals do not match the normal development for their genetic sex Caused by: (1) two ova, each fertilized by a different sperm (one X-bearing, one Y- bearing) unite (instead of becoming twins), (2) an XX baby being exposed to more T will be partly masculinized Some are fertile as M or F,  no cases of fertile as both ~1/100 of children are born with some degree of genital ambiguity (~1/2000, status as M or F is uncertain)  some question these stats because this information is confidential Congenital Adrenal Hyperplasia (CAH) Most common cause of hermaphroditism In utero, the developing child produces more T than usual (as a result of a genetic condition) For males, no problem. Females experience varying degrees of masculinization of their external genitals – ovaries and other internal organs are generally normal After birth: ○ Hormone levels are medically returned to normal ○ Corrective surgery on masculine genitals Effects: ○ Toy preference: intermediate between preferences of non-CAH boys and non-CAH girls ○ The greater the exposure to T, the greater the preference for boys’ toys ○ CAH girls perform slightly better than non-CAH girls on spatial tasks ○ During adolescence, CAH girls’ interests are intermediate between those of non- CAH boys and non-CAH girls  e.g., compared to non-CAH girls, CAH girls read more sports magazines and fewer style magazines ○ As adults, CAH females exhibit more aggressive behaviour, less interest in infants, greater interest in rough sports, and are more likely to be in male-dominated occupations (compared to non-CAH Fs) (from a 2010 study) ○ Sexual preferences: although most lagged behind non-CAH Fs in dating and marriage  70% are heterosexual and 30% are homosexual or bisexual (the prenatal androgenization likely explains the increased incidence of a masculinized sexual orientation) Testicular Feminization (from textbook) XY chromosome individual may have a deficiency in receptor for androgens, so the androgens have little effect. Also known as androgen insensitivity Produces smaller than average penis, external appearance of female, and during puberty, breasts develop and hips broaden, but menstruation does not occur, and no pubic hair. Issues of Gender Assignment and Rearing In the past, physicians recommended that intersex children be raised as girls ○ Surgery performed to make them look more feminine (easier than surgery to make them look more masculine) ○ It was assumed that children consistently raised as female would accept that identity Not the case! Males (XY) born with conditions that thwart development of male genitals and who were raised as females develop typical male interests and ask to be reassigned as males Current guidelines ○ Be honest with the person/family ○ Identify gender based on predominant external genital appearance ○ Raise child as consistently as possible, but be prepared for all possible attractions Discrepancies of Sexual Appearance Some genetic males (XY) fail to produce an enzyme (5a-reductase 2) that converts T to dihydrotestosterone (which is actually more effective at masculinizing the external genitals) ○ Most look female at birth and raised as girls ○ But a penis develops during adolescence and puberty (which is the normal M puberty) Most then accept a male gender identity These “females-turned-males” developed a male gender identity and directed their sexual interest toward Fs  but, their brains were exposed to T https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 4/6 11/7/24, 4:00 PM OneNote Sexual Orientation Homosexual behaviour occurs in many species. One’s sexual orientation is recognized by Ms earlier than Fs. Feminine behaviours in childhood and adolescence correlate strongly with homosexuality in males; early masculine behaviours do not correlate as high with sexual orientation in females. (Exotic Becomes Erotic Theory) ○ Child sees other children as different in childhood (typical male sees typical female as different) ○ In adolescence, this difference becomes attraction ○ Masculine girl- the "different" feminine females become attractive later on ○ Feminine boy- the "different" masculine males become attractive later on A higher % of Fs experience same-sex attraction, and Fs are more likely to switch their sexual attraction. The case for a biological predisposition toward homosexuality seems stronger for Ms. Behavioural and Anatomical Differences Subtle average behavioural and anatomical differences between heterosexuals and homosexuals exist ○ Heterosexual M slightly taller and heavier ○ Bones of the arms, legs, and hands are longer in heterosexual M than in homosexual M, and longer in homosexual F than in heterosexual F (differences most apparent among caucasians) ○ Homosexual M use landmarks more often when giving directions (as heterosexual F are likely to do); heterosexual M use distance amounts and directions (N,S,E,W) Is sexual orientation genetic? There is a genetic contribution to homosexuality, but the amount of the contribution is unclear. Research on twins: ○ American Research (1990s) For males: 52% vs. 21% (MZ vs. DZ) For females: 48% vs. 15% (MZ vs. DZ) ○ Swedish Research (2010) For males: 10% vs. 5% (MZ vs. DZ) For females: 11% vs. 7% (MZ vs. DZ) ○ No single particular gene has been identified The X Chromosome and Homosexuality Homosexual Ms are more likely to have homosexual uncles and male cousins on the maternal side of the family than the paternal side (13% vs. 6%): ○ Might the X chromosome be involved? Maybe. ○ Some research has concluded the Xq28 region of the chromosome is similar in homosexual M relatives. ○ Controversial. Some research has failed to replicate. ○ No link between Xq28 region and homosexuality in Fs The Autosomes and Homosexuality Autosomes: the other 22 chromosomes that are not XY Ellis et al. (2008): looked for differences in four areas known to be genetic: (A) eye colour, (B) hair colour, (C) blood type, and (D) Rh factor ○ (A) and (B) – no differences ○ (C) – differences: homosexual M less likely to have Type A, homosexual F more likely to have Type A (chr. #9) ○ (D) – differences: Rh- factor more common in homosexual M and F (chr. #1) (type A+) Genes on chromosomes 7, 11, 12, 13, and 15 (11 and 15, only in Ms) connected to having at least one same-sex experience, but they were not related to identified sexual orientation Same genes involved in olfaction (only M), risk-taking behaviour, male-pattern baldness (only M), depression, schizophrenia, and bipolar disorder (only F) Prenatal influences on Sexual Orientation Sexual orientation is not related to adult hormone levels Homosexual Ms and Fs tend to have normal hormone levels for their biological sex BUT… it is possible that sexual orientation depends on T levels in the brain during a sensitive period of development (prenatal). Diethylstilbestrol has masculinizing effects on the development of the unborn child’s brain ○ In Fs: Those exposed: 17% homosexuality Those not exposed: 0% homosexuality Male Homosexuality and Having Older Brothers Probability of homosexuality is higher among Ms who have older biological brothers With each older brother, probability increases by ~35% of the previous probability level No other sibling relationship makes a difference: the key is how many previous sons mom has had What’s going on? A Y-chromosome-linked protein (NLGN4Y) important to M brain development gets into mom’s bloodstream, and her immune system responds by creating antibodies. These antibodies accumulate and can cross the placental barrier and enter the brain of subsequent M fetuses, and that may alter the functions in the brain, changing the direction of how the M later develops his sense of attraction. Prenatal Stress and Sexual orientation https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 5/6 11/7/24, 4:00 PM OneNote Research with rats – males displayed more feminine sexual behaviour when mom was stressed before they were born. ○ No impact of prenatal stress on Fs’ sexuality. What about humans? Not much research  a few studies found that mothers of homosexuals experienced very high levels of stress during pregnancy. Stress elevates levels of cortisol that can cause a decrease in T production (e.g., in adults who are stressed, sex drive is low) Brain Anatomy Differences in brain anatomy between homosexuals and heterosexuals exist: ○ On average, the homosexual’s brain is shifted towards the opposite sex’s brain in some ways … BUT, for many reported differences there is no clear connection to sexuality itself ○ E.g., in heterosexual Ms, the right hemisphere is slightly larger than the left and in heterosexual Fs, the two hemispheres are of almost equal size  for homosexual Ms, the two hemispheres are of almost equal size, and for homosexual Fs, the right hemisphere is slightly larger Sexual Orientation ○ Homosexual men tend to have: A larger anterior commissure (bundle of nerves connecting the right and left temporal lobes) – some research has failed to replicate A larger suprachiasmatic nucleus (1.7x larger; 2.1x as many cells) A smaller third interstitial nucleus of the anterior hypothalamus (INAH-3)  contains cells with androgen receptors – theirs is roughly the size of the INAH-3 in heterosexual women This is the strongest biological indicator of sexual orientation Sometimes called the sexually dimorphic nucleus Typical sizes of Interstitial Nucleus 3 of the Anterior Hypothalamus On the average, the volume of this structure was more than twice as large in a sample of heterosexual men (left) than in a sample of homosexual men (right), for whom it was about the same size as in women. Are these differences causes or consequences? Do differences in INAH-3 influence sexual orientation or does sexual activity influence the size of the hypothalamic neurons? DONE https://onedrive.live.com/redir?resid=1313C96006B75820%2113751&authkey=%21Ap8e7bM09WS3LNg&page=Edit&wd=target%28PSY 336.one%7C9fada921-1… 6/6