Variations in Sexual Behavior:

Evolutionary Interpretations of Mating Behavior:

• Interest in multiple mates:
  • Men are more likely to be interested in brief sexual relationship with many partners:
    • Spreading the gene
    • Women can only have one pregnancy per 9 months
• What men and women seek in a mate:
  • Both: healthy, intelligent, honest, physically attractive
  • Women: have more additional ones, ex. good providor
  • When a woman is pregnant she needs help getting food
  • Men prefer young partners: younger women are more likely to be fertile, men remain fertile longer
• Differences in jealousy:
  • Men are more likely to be jealous than women
  • A man has to be certain the children are his own that he’s providing for, a woman knows the children are her own
• Evolved or learned?
  • We can’t prove that these behaviors are evolutionary (-> biological/genetic)

Gender Identity and Gender Differentiated Behaviors:

Intersexes:

• Some people develop an intermediate appearance because of an atypical hormone pattern (ex. a female exposed to more testosterone than normal can be partly masculinized)
• Most common cause: genital adrenal hyperplasia (CAH, overdevelopment of adrenal glands from birth)
• Normally adrenal glands have a negative feedback relationship with the pituitary gland (it secretes ACTH which stimulated the adrenal gland)
• The adrenal gland secretes several hormones, like cortisol, which feeds back to decrease ACTH
• Some people have a genetic limitation in their ability to produce cortisol, so it secretes too much ACTH, which causes the adrenal gland to secrete more other hormones (including testosterone) -> a female with this becomes masculinized in their external genitals -> they become intermediate between male and female
• Hermaphrodite: individuals whose genitals do not match the usual development for their genetic sex, ex. a testis one one side and a ovary on the other side
• Intersexes/pseudohermaphrodites: people whose sexual development is intermediate/ambiguous
• Interests and Preferences of CAH Girls:
  • Mostly reared as girls
  • They show preference for “boy-toys”
  • Many report no sexual fantasies (neither men nor women) which is unusual

Testicular Feminization:

• Androgen insensitivity/testicular feminization: have XY chromosomal pattern and genital appearance of a female, they produce normal amounts of androgens (including testosterone) but they lack the androgen receptor that enable it to activate the genes in a cell’s nucleus
• Ranges from a smaller than average penis to genitals like a female
• Issues of Gender Assignment and Rearing
• Some girls with CAH look as much male as female
• Some males have very small penises
• How should they be reared?
  • 1950’s: doctors said all intersex people shoud be reared as girls, using surgery if necessary, they thought they would accept that gender that way, BUT: many have complained, they have no feelings in their vagina and a lot of scarring, they wanted their original structures
• General recommendations:
  • Be honest with them and do nothing without their informed consent
  • Identify the child as male/female based on the closest appearance
  • Rear the child as consistent as possible, be prepared for what their sexual preference might be
  • Don’t perform surgery, it impairs the erotic sensation

Discrepancies of Sexual Appearance

• Some children were exposed to male levels of testosterone during early development, they look like girls at birth and are reared like that, but in puberty the body makes increased amonts of a different enzyme that converts testosterone to dihydrotestosterone, and they grow a penis scrotum
• They react by acting now as a boy, with a male gender identity and direct their sexual interest toward females
• It depends on the pearson, not the rearing what they want to identify themselves with, it also doesn’t depend on the hormones entirely

Possible biological Bases of Sexual Orientation

Genetics:

• Some animals show homosexual tendencies related to genes, but in humans, twin studies showed that genes could be related to it but not 100%

Hormones:

• Clearly NOT related to sexual orientation
• But it might have something to do with hormone levels during a sensitive period
• In animals studies it did show that, but the animals also looked more like the other sex
• In humans, homosexual men and heterosexual women have shorter arms and legs -> the women are more masculinized and the men are more feminized
• In some ways but not other male homosexual brains are shifted towards female-typical direction and female homosexual bains are shifted toward male-typical direction

Prenatal Events:

• The more older brothers a man has the more likely are they going to be homosexual, but not for women -> a mother’s immune system sometimes reacts against a protein in a son and then attacks subsequent sons enough to alter their development but that would mean that if one son is homosexual, all the younger ones would be too, but it’s not true
• Prenatal stress can alter sexual development, in rats it made the males act sexual towards other males but they had normal male anatomy -> it could be because stress releases endorphins which antagonize the effects of testosterone in the hypothalamus, it also releases corticosterone, which decreases testosterone release. The long term effect: several changes in the structure of the nervous system, making the males anatomically closer to females

Brain Anatomy:

• The anterior commissure is larger in women than in men, and it’s as large in homosexual men as in women, if not larger, but it has no known relationship to sexual behavior
• The suprachiasmatic nucleus (SCN, controls circadian rhythm) is also larger in homo men than in hetero men but it isn’t clear how it relates
• The thirds interstitial nucleus of the anterior hypothalamus (INAH-3), is more than 2x as large in men than in women, in homo men it was as small as womens’.