Sexually dimorphic behaviors: differ in males and females, due to hormoens present before/after birth.
Chromosomal sex determined at time of fertilization.
Production of gametes and fertilization: all cells have 23 pairs of chromosomes, DNA w/ genetic info that
programs development. Gametes: ove/sperm – mature reproductive cell, contain one member of each of 23
pairs. Last pair is sex chromosomes X and Y(male).
Development of sex organs: Y controls development of glands that produce male sex hormones.
o Gonads: testes/ovaries, first to develop, make ova/sperm and secrete hormones. Sry gene makes
protein that binds to DNA of cells in undifferentiated fetus gonad and causes them to become testes.
If no Sry, then gonads ovaries. Hormones effect sexuality in 2 ways: organizational during
prenatal (influence development of sex organs/brain, permanent), activational (later in life, activate
production of sperm/induce ovulation etc).
o Internal sex organs: bisexual early on, one precursor develops in third month. Mullerian system:
fimbriae, Fallopian, uterus, vagina. Wolffian: epididymis, vas deferens, seminal vesicles, develops if
hormones secreted by testes. Testes secrete two hormone types: anti-Mullerian peptide
defeminizing, and androgen steroids stimulate Wolffian, masculinizing – testosterone secreted by
testes, converted by 5a reductase into dihydrotestosterone. Androgen insensitivity syndrome:
genetic mutation prevents formation of functioning androgen receptors (gene on X), gonads becomes
testes and secrete anti-Mullerian and androgens, but no androgen receptors prevents masculinizing
effect, so male organs don’t develop, and neither do female, because anti-Mullerian hormone still
has defminizing effect. Person has female body but no children. Persistent Mullerian duct
syndrome: from failure to make anti-Mullerian hormone or absence of receptors for hormone.
Androgens are masculinizing but no defeminization, so person has both sets of internal sex organs.
Hormone made by female sex organs not actually needed for Mullerian development – “nature’s
impulse is to create female.” Turner’s syndrome: only X chromosome, no gonads develop, but still
o External genitalia: visible sex organs, penis/sctorum, labia/clitoris/vagina. Female genitalia naturally
develop, need dihydrotestosterone to become male.
Sexual maturation: secondary sex characteristics in puberty occur when cells in hypothalamus secrete
gonadotropin-releasing hormones GnRH, stim production/release of two gonadotropic hormones
(follicle-stimulating hormone FHS, luteinizing hormone LH) from pituitary, stimulate gonads to produce
their hormones. Leptin secreted by well-nourished fat cells signals brain to suppress appetite, plays role in
determining onset of puberty in females. In response to gonadotropins, gonads secrete steroid sex hormones:
ovaries make estradiol (estrogen), and testes produce testosterone (androgen), both produce a little of the
other, causing axillary/public hair in women. Both halt skeletal growth.
Hormonal control of female reproductive cycle: menstrual in primates, estrous in other species. Cycles
controlled by hormonal secretions of pituitary and ovaries, which interact. Cycle begins when anterior
pituitary secretes gonadotropin, stimulates growth of ovarian follicles, small spheres of epithelial cells in
each ovum. As they mature, secrete estradiol, causing growth of uterus lining. Increased estradiol triggers
release of LH, which causes ovulation – follicle ruptures, becomes corpus luteum, produces estradiol and
progesteronegestation. Ovum released, enters Fallopian tube, goes to uterus. If not fertilized, corpus
luteum stops making estradiol/progesterone, lining of walls comes off, menstruation.
Hormonal control of sexual behavior in lab animals: all males have intromission, pelvic thrusting,
ejaculation. Male rat has pelvic thrusting, intromission, ejaculation, and refractory period, will become
excited again by presence of new female. Oxytocin released at orgasm, Prolactin released after
ejaculation, inhibits male sex behavior. In females, lordosis response is to assume posture to expose
genitals, if in estrous state, will have active role in initiating copulation. Sexual behavior depends on
estradiol and progesterone together: increases receptivity, proceptivity, and attractiveness.
Organizational effects of androgens on behavior: masculinization/defeminization. 339
Effects of pheromones: carry messages from one animal to another., effect reproductive physiology or
behavior. Lee-Bott: females housed together stop estrous cycles. Whitten: cycles restart in sync if exposed
to male odor. Vandernbergh: acceleration of onset of puberty in female caused by male odor. Bruce: pregnancy will fail if exposed to a different male rat. Vomeronasal organs VNO: sensory receptors in nasal
passage, projects to accessory olfactory bulb, to medial nucleus of amygdala, detects pheromones,
responsible for all effects above. Humans have VNO too but considered to be vestigial organ. AND in male
sweat has good effect on women but not men, and EST in female sweat activates men but not women.
Human sexual behavior: influenced by activational effects of gonadal hormones, organizational effects.
Women: ovarian hormones control willingness, ability to mate, but in higher primates ability not controlled
by hormones, no physical barriers. Men will initiate any time, women initiate especially around ovulation,
highest levels of estradiol, if they want to become pregnant especially. Female sexual interest also
amplified by androgens. Men: without testosterone, sperm production and sexual potency ceases. Affected
by rank/experience. Anticipation of sexua