Sapolsky: 15. Human Sexual Behavior I

Robert Sapolsky, Stanford

https://www.youtube.com/watch?v=LOY3QH_jOtE

Evolution of species
Evolution of population
Genetics
Perinatal bio
Perinatal ?
Chronic Hormonal
Cutton
Acute Hormones
Releasing Stimuli
Neurobio
Behavior

Why were they in such a hurry at the end? Proximal explanation: it feels good Distal explanation: hormones, nerve endings, stimuli, feedback loop, etc

close vs far

Proximal mechanisms: Releasing Stiumli and Neurobio Distal mechanisms: evolution, perinatal bio, etc

highly conserved fixed action patterns across many species most vertebrate species using pelvic thrusting, orgasms, ejaculation, lordotic reflex (lordosis, presenting, bending backward)

selectivity within species

chaining of behavior and releasing stimuli male behavior stimulates female behavior which stimulates male behavior which stimulates…

libido, arousal, motivation

attractivity, proceptivity, receptivity

motivation, performance

female orgasm shared by other primates not necessary for conception but may increase likelihood of facilitates fertilization 1. increased vaginal fluids increases motility of sperm 2. exhausts the female leaving her horizontal 3. feels good so more likely to do it again but, no correlation between fertility of a woman and her propensity for orgasm

spandrel - a feature arising a byproduct rather than an adaptation, with no clear benefit for fitness and survival

orgasm is a spandrel in women nipples are a spandrel in men

human specializations are these things unique to humans: non-reproductive sex: humans, bonobos, dolphins foreplay homosexuality egalitarian sex (in many species, only one male and one female are chosen for reproduction) private - in no other species is the majority of sexual behavior done in private confusing sex with aggression or violence masturbation fantasizing - we have no way to know whether other species fantasize marriage - universal across human cultures. some other species have monogamous pair-bonding. Humans have social monogamy but not sexual monogamy. between 10 and 40% of children are fathered by someone other than the sperm donor. cheating romance - new, 3 or 4 centures that romance should persist throughout a marriage - novel concept, 30 or 40 years old divorce - average marriage across all cultures: 2 to 4 years, 2 to 4 years is the period of children being dependent on a high degree of parenting, and is the interbirth interval serial monogamy - with the lag time between relationships equal to the interbirth interval

non-human specializations hermaphrodite an individual changes sex opportunistically parthenogenic - an individual reproduces without the benefit of anyone else's genetic input

Gender Differences 1. brain regions preferentially involved differs between genders

females hotspots ventral medial hypothalamus - receptors for estrogen, progesterone, midbrain spinal column - the lordotic reflex is exclusive to females

male hotspots medial preoptic area (of the hypothalamus), receptors for testosterone, androgen. sexual performance amygdala - sexual motivation (how are sexual motivation and aggression related?) autonomic nervous system parasympathetic nervous system establishes the erection, sympathetic nervous system needed for ejaculation same for female clitoral erection slower recovery time in females than males vascular erection (human, longer) muscular erection (rat, faster)

2. brain regions differ in size per gender sexual dimorphism INAH Cluster of Nucleii in the Hypothalamus, twice the size in men, statistically significant

Same in both genders

Male and female orgasm

problems in males, too rapid transition from parasympathetic to sympathetic (premature ejaculation)

problems in females, failure of transition from parasympathetic to sympathetic (no orgasm). Is this a pathology, or a normal human variability?

Neurobiology of Pleasure, Anticipation, Reward

Dopamine - identical role in both sexes, huge role

Dopamine path: from Ventral Tegmental area to nucleus sucumbens to many places in the brain

If this path is depleted, no interest in sexual behavior. Loss of libido proceptivity. Like in clinical depression. One of the defining symptoms of clinical depression: loss of libido proceptivity.

meso-limbic dopamine system, central to the reinforcing aspects of sexual behavior

dopamine system not so much about reward as about anticipation driving goal-directed behavior

show a man a picture of attractive woman making eye contact, dopamine system activates show a man a picture of unattractive woman looking away, dopamine system activates

monkey gets a reward after 10 lever presses dopamine level goes up in monkey when he presses the button, not when he gets the reward 50% of the time, randomly, monkey gets a reward after 10 lever presses “maybe” dopamine level goes thru the roof “intermittent reinforcement” 25% or 75% you get some smaller increase in dopamine 50% gets maximum dopamine, therefore maximum goal-directed bahavior like in vegas, make it seem like 50% probability to get maximum goal-directed behavior

“a relationship is the price you pay for the anticipation of it”

pair-bonding, d1, d2 receptors dopamine receptor subtypes d1 d2 in monogamous species, right after mating, when a pair-bond is first formed, d2 goes down, d1 goes up if you drive down the d2 levels before mating, they don't form a pair-bond if you prevent the drop in d2, or prevent the rise in d1, they will pair-bond and 8 minutes later go pair-bond with somebody else d1 seems to mediate the monogamous features of the pair-bond

you have a beloved put you in a brain scanner show photos of people you know, with subliminal photos of your beloved knowing your beloved for 2.5 weeks, the photos stimulate the dopamine system after 5 years, the photos stimulate anterior singulate, the empathy comfort system