Transcript Document
Sexual Behaviors PSYC 370
Sex and Hormones
• Sexual reproduction between two individuals increases variation in the gene pool.
• Variation in the gene pool of a species enables quick evolutionary adaptations to change in the environment.
• Also corrects genetic errors and disadvantageous mutations.
Sex and Hormones
• Widespread communication throughout the body is accomplished through the release of hormones.
• Two kinds of hormones include: – Steroid hormones – Sex hormones
Sex and Hormones
• Steroid hormones are derived from cholesterol, contain four carbon rings and exert their effects in three ways.
1. Binding to membrane receptors like neurotransmitters.
2. Entering cells and activate certain kinds of proteins in the cytoplasm.
3. Binding to chromosomes where they activate or inactivate certain genes.
Sex and Hormones
• • • The sex hormones are a special kind of steroids, released mostly by the gonads and to a lesser degree by the adrenal glands.
– affect the brain, genital and other organs Two types of sex hormones include: 1. Androgens 2. Estrogens Both sexes have these categories in varying quantities .
Sex and Hormones
• Androgens are a groups of sex hormones that include testosterone and others.
• Generally referred to as “male hormones” because men have higher levels than women.
Sex and Hormones
• Estrogens include estradiol and others and are referred to as “female hormones” because women have higher levels.
• Progesterone is a type of hormone that prepares the uterus for the implantation of a fertilized ovum and promotes the maintenance of pregnancy.
Sex and Hormones
•
Sex limited genes
are those activated by androgens or estrogens and control most of the differences between male and female.
– Example: estrogens activate the gene for breast growth; androgens activate the gene for the growth of facial hair in men.
• Sex hormones increase or decrease the rate of apoptosis in various regions of the brain. – Certain areas are slightly larger in males or females
Sex and Hormones
• Sex hormones can have the following effects: 1. Organizing effects occur mostly at sensitive stages of development. -Determine whether the brain and body will develop male or female characteristics 2. Activating effects occur at any time of life and temporarily activate a particular response.
Sex and Hormones
• The distinction between the activating and organizing effects of hormone is not absolute.
– Example: hormones early in life can exert temporary effects; during puberty hormones can also induce long-lasting structural changes
Sex and Hormones
• Obvious differences can exist between the reproductive organs and the gonads of males and female.
• Sexual differentiation begins with the chromosomes.
• Female mammal has two X chromosomes and a male has an X and a Y.
• During an early stage of prenatal development, both male and female have a set of Mullerian ducts ducts and a set of as well as primitive gonads.
Wolffian
Sex and Hormones
• Wolffian ducts are the precursors to other male reproductive organs.
– Develop into the vas deferens and seminal vesicles.
• Mullerian ducts are precursors to the female’s oviducts, uterus, and upper vagina.
Sex and Hormones
• The male Y chromosome includes the SRY gene which causes the primitive gonads to develop into testes , the sperm-producing organ.
• The developed testes produce the hormone testosterone .
• Testosterone induces the development of the penis and scrotum.
• Females are not exposed to high testosterone levels and their gonads develop into ovaries , the egg-producing organs.
Sex and Hormones
• Sensitive periods are early periods when hormones have long-lasting effects.
• Sexual differentiation depends mostly on the level of testosterone during a sensitive period.
• The human sensitive period for genital formation is about the
third
and
fourth
of pregnancy.
month
Sex and Hormones
• Female rats exposed to testosterone shortly before or after birth are partly masculinized in anatomy and behavior.
– Clitoris grows larger than normal – At maturity, pituitary and ovaries produce steady levels of hormones instead of cycles – Parts of the hypothalamus appear more male – Sexual behavior becomes masculinized
Sex and Hormones
• Extra estradiol does not determine whether the individual looks female or male.
• Estradiol and other estrogens do modify various aspects of the development of the brain and the internal sexual organs.
• The absence of sex hormones generally leads to female-looking external genitalia • If a male rat lacks androgen receptors or is castrated, it develops female-like anatomy and behavior.
Sex and Hormones
• Sex hormones early in life bind to receptors in specific areas of the hypothalamus, amygdala, and other brain areas and produce anatomical and physiological differences.
• The sexually dimorphic nucleus is an area in the anterior hypothalamus that is larger in the male and contributes to control of male sexual behavior.
• Parts of the female hypothalamus generate a cyclical pattern of hormone release; the hypothalamus of a male cannot.
Sex and Hormones
• In adulthood, sex hormones exert activating effects to temporarily modify behavior.
• Behavior can also influence hormone secretion.
• Hormones do not cause behavior but rather alter the activity in various brain areas to change the way the brain responds to certain stimuli.
• Hormones also change sensitivity in the penis, vagina and cervix.
Sex and Hormones
• Sex hormones facilitate sexual behavior.
• Arousal also depends on previous sexual experience.
• Sex hormones activate sexual behavior by enhancing sensations.
• Estrogens increase the sensitivity of the
pudendal nerve
, which transmits tactile stimulation from the pubic area to the brain.
Sex and Hormones
• Testosterone and estradiol trigger the release of dopamine by the MPOA and other areas.
• Dopamine stimulation of D 1 and D 5 is associated with sexual arousal.
receptors – Facilitates erection of the penis and sexually receptive postures in females • Higher concentrations of dopamine stimulate D2 receptors and lead to orgasm.
• Serotonin activity decreases sexual activity by blocking dopamine release.
Sex and Hormones
• Humans are less dependent on current sex hormones than other species but changes can increase or decrease sexual arousal.
• For males, levels of testosterone correlate positively with sexual arousal and the drive to seek out partners.
Sex and Hormones
• Decreases in testosterone levels generally decrease male sexual activity and interest.
– Example: castration • Impotence erection.
is the inability to maintain an – usually caused by impaired blood circulation, not low testosterone.
• Erection partially depends on testosterone increasing the release of nitric oxide.
– facilitates the hypothalamic neurons and increases blood flow to the penis.
Sex and Hormones
• Most sex offenders have normal testosterone levels.
• Hormone levels do not completely explain the behaviors.
• Testosterone reduction has been tried as a means of controlling sex offenders as it reduces sexual activities.
• Results favorable for those who continue taking medication, but dropout rate is high.
Sex and Hormones
• In women, the hypothalamus and pituitary interact with the ovaries to produce the menstrual cycle.
• The menstrual cycle about 28 days.
is the periodic variation in hormones and fertility over the course of
Sex and Hormones
• After the end of a menstrual period: – the anterior pituitary releases follicle stimulating hormone (FSH) – FSH promotes the growth of a follicle in the ovary.
– The follicle nurtures the ovum and produces estrogen.
• Towards the middle of the menstrual cycle, the follicle builds up receptors to FSH.
• As a result, the follicle produces increasing amounts of estradiol , a type of estrogen.
Sex and Hormones
• Increased estradiol causes the anterior pituitary to increase release of FSH and luetinizing hormone (LH).
• FSH an LH cause the follicle to release an ovum.
• The remnants of the follicle release the hormone progesterone.
– prepares the uterus for implantation of a fertilized ovum – inhibits the further release of LH
Sex and Hormones
• If the ovum is not fertilized, the lining of the uterus is cast off and menstruation occurs.
• If the ovum is fertilized, the levels of estradiol and progesterone increase gradually throughout pregnancy.
Sex and Hormones
• Birth control pills prevent pregnancy by interfering with the usual feedback cycle between the ovaries and pituitary.
• The “combination-pill” contains both estrogen and progesterone and prevents the surge of FSH and LH that would release an ovum.
– also thickens the mucus of the cervix making it harder for the sperm to reach the egg.
Sex and Hormones
• The periovulatory period is the time of maximum fertility and high estrogen levels when ovulation occurs.
• Studies suggest that women become more sexually responsive during this time when estrogen levels are high.
– Show increased attention to sex-related stimuli.
– show increased mate preference towards men who act and look more masculine.
Sex and Hormones
• Oxytocin is a pituitary hormone also important for reproductive behavior.
• Stimulates contraction of the uterus during delivery of a baby • Stimulates the mammary gland to release milk.
• Released during orgasm and triggers a state of complete relaxation.
• Facilitates formation of pair bonds between mating partners and mother and infant
Sex and Hormones
• Hormones released around the time of giving birth facilitate maternal behavior in females.
• Late in pregnancy, the female secretes large amounts of estradiol, prolactin, and oxytocin.
• Prolactin is necessary for milk production.
• Oxytocin is associated with maternal behavior and social attachment.
Sex and Hormones
• Females also change patterns of hormone receptors.
• Late in pregnancy, the brain increases its sensitivity to estradiol in areas responsible for maternal behavior, but not for sexual behavior.
• The hormonal changes increase the attention of the mother to the young after birth.
• Hormones also increase activity in the medial preoptic area and the anterior hypothalamus.
Sex and Hormones
• Vasopressin is a hormone synthesized by the hypothalamus and secreted by the posterior pituitary gland.
– associated with establishing long-term bonds in some species.
• Mothers are also stimulated by the odors of their babies.
– Infant rats release chemicals that stimulate the mother’s vomeronasal organ.
Sex and Hormones
• • Mammals have two mechanisms for stimulating maternal behavior: 1. Hormones in the early phase compensate for the lack of familiarity with the young.
2. Later experience maintains the maternal behavior as hormones decline.
Although hormonal changes are necessary to nurse a baby, they are not necessary to elicit care for a baby by humans.
Variations in Sexual Behavior
• A wide degree of variation exists between people in terms of frequency of sexual behavior, preferred types of sexual activity, and sexual orientation.
• Evolutionary explanations are controversial in explaining mating behavior.
Variations in Sexual Behavior
• Gender differences in sexual behavior include the following: – Men are more likely to seek multiple sex partners, especially for short-term encounters.
– Women are more likely to be concerned about a mates earning potential: men are more likely to be concerned about a mate’s youth.
– Men usually show greater jealousy at indications of sexual infidelity.
Variations in Sexual Behavior
• Buss (2000) argues that gender differences reflect past evolutionary pressures.
• Men are interested in brief sexual relationships with multiple partners because such a strategy increases the likelihood of his genes being passed along to the next generation.
Variations in Sexual Behavior
• Research has also suggested that women can gain from having multiple sexual partners as well.
• Multiple mates increases resources available to her child and herself.
• No direct evidence suggests that specific genes influence whether people prefer single or multiple mates.
Variations in Sexual Behavior
• Both men and women prefer a mate that is healthy, intelligent, honest, and physically attractive.
• In almost all cultures, women prefer mates who are likely to be good providers.
• Evolutionary explanations suggest that choosing a father who is likely to be a good provider aids the women while she is pregnant or caring for a small child.
Variations in Sexual Behavior
• Men tend to prefer a young partner.
• Evolutionary explanations suggest that this preference exists because younger women are more likely to be fertile than older women.
• Men remain fertile well into old age so preference for a young mate for women is not as pronounced.
Variations in Sexual Behavior
• Evolutionary explanations of gender differences in jealousy suggest that men need to be sure that the children he supports are his own.
– Unfaithful wives threaten this certainty.
• Women are always sure that the child is their own.
• Although cultures vary in attitudes towards infidelity, no culture exists where infidelity is more acceptable for women.
Variations in Sexual Behavior
• Although mating habits of people can be explained in terms of increasing the probability of passing on one’s genes, we can not assume a genetic basis.
– Behaviors and preferences may be a product of learning.
• More data, especially about the effects of particular genes, is needed to draw conclusions.
Variations in Sexual Behavior
• Gender identity refers to how we identify sexually and what we call ourselves.
• Biological differences are generally referred to as “sex differences”.
• Differences that result from people’s thoughts about themselves as male or female are referred to as “gender differences”.
Variations in Sexual Behavior
• Most people have a gender identity that matches their external appearance. • Some people have a gender identity that is opposite their biological sex.
• Psychologists and researchers once believed that gender identity was learned and more a product of rearing and experience. • Current evidence strongly suggests that biological factors, especially prenatal hormones, play a large role in gender identity.
Variations in Sexual Behavior
• Intersexes are people that have anatomies intermediate between male or female.
• Poorly developed or ambiguous genitalia can be caused by: • XY males have a mutation of the SRY gene • Born with an XX chromosome pattern but an SRY gene translocates from the father’s Y chromosome onto another chromosome. • An atypical hormone pattern occurs or a mutation of testosterone receptors occurs before birth.
Variations in Sexual Behavior
• Congenital adrenal hyperplasia (CAH) is an overdevelopment of the adrenal glands from birth • Most common cause of the intersex condition.
• Caused by a genetic defect in which cortisol production leads to overstimulation of the adrenal gland.
• Overstimulation of the adrenal gland leads to extra testosterone production.
– The female fetus becomes partly masculinized.
Variations in Sexual Behavior
• Hermaphrodites are individuals whose genitals do not match the usual development for their genetic sex.
• An estimated 1 out of 100 children is born with some degree of genital ambiguity.
• 1 in 2000 has enough genital ambiguity to make the sex uncertain.
Variations in Sexual Behavior
• The brains of genetic females with CAH are exposed to higher than normal levels of testosterone during prenatal and early postnatal life.
• Research indicates that CAH girls show a greater preference for boy-typical toys than do other girls.
• During adolescence and early adulthood, they also show partly masculinized interests.
• Sexual interest and activity also differs for CAH girls as well.
Variations in Sexual Behavior
• Androgen insensitivity or testicular feminization is a condition in which individuals with an XY chromosome pattern have the genital appearance of a female.
• Production of androgens remains normal but they lack the androgen receptor that enables it to activate genes in a cell’s nucleus.
• Condition occurs in various degrees from a smaller than average penis to genitals that develop a female appearance.
Variations in Sexual Behavior
• Physicians have traditionally recommended that intersex people be reared as girls.
– surgery was often conducted to make them look more feminine.
– Assumed that children consistently raised as female would accept that identity.
• Many intersex people protest against such surgery and suggest that an informed consent would have been preferred.
Variations in Sexual Behavior
• Some genetic males fail to produce an enzyme that converts testosterone to dihydrotestosterone.
• Most look female at birth but a penis develops during adolescence and puberty.
• Most then accept a male gender identity.
– Brain is exposed to testosterone during early development.
Variations in Sexual Behavior
• Many genetic males born without a penis or who had the penis accidentally removed and who were raised as a girl ask to be reassigned as males.
• Many who remain female feel discontent or conflict with being female.
• Such cases indicate that although hormones do not determine gender identity, they do play an important role.
Variations in Sexual Behavior
• Research has identified several predisposing factors in genetics and prenatal environment for male homosexuality.
• Genetic and biological predisposition appears weaker for women. • Gender-typed behaviors in childhood are a stronger predictor of sexuality for men than compared to women.
• Higher percentage of women acknowledge physical attraction to both sexes and switch between sexual orientations.
Variations in Sexual Behavior
• Subtle average behavioral and anatomical differences between heterosexual and homosexual include: – Length of bones in the arms, legs and hands – Percentage of hair whorl direction – Use of landmarks versus distances to give directions • Implies sexual orientation is an integral part of the individual.
• But shifting of behavior to the opposite sex does not equally apply to both sexes.
Variations in Sexual Behavior
• Studies of twins suggest sexual orientation is influenced by genetic factors.
• Probability of homosexuality is highest in monozygotic twins and lower in dizygotic twins, and even lower in siblings and adopted brothers or sisters.
• No single particular gene has been identified.
• Each of several genes may have an influence.
Variations in Sexual Behavior
• Studies also suggest a higher incidence of homosexuality among the maternal relatives of homosexual men.
• These results suggest a gene on the X chromosome that a man receives from his mother may play a role.
• Other studies have not replicated this result and thus the findings are inconclusive.
Variations in Sexual Behavior
• Sexual orientation may be influenced by testosterone levels during sensitive periods of brain development.
• Studies of male animals deprived of testosterone early in life show sexual interest in other males as adults.
• Studies of female animals exposed to testosterone during early development show an increased likelihood of mounting behavior.
Variations in Sexual Behavior
• Evolutionary explanations for homosexuality suggest: – Genes are maintained by kin selection – Genes that produce homosexuality increase probability of female relatives reproducing – Several genes produce advantages for reproduction, but certain combinations lead to homosexuality.
– Homosexuality relates to activation or inactivation of genes.
Variations in Sexual Behavior
• Sexual orientation is not related to adult hormone levels.
• May be influenced by exposure to testosterone during sensitive periods.
Variations in Sexual Behavior
• The probability of homosexual orientation is also higher among men with older brothers.
• Number of previous sisters has no effect nor do these effects apply to females.
• Results suggest that a mother’s immune system may react against a protein in a son and attacks subsequent sons to alter development.
Variations in Sexual Behavior
• Prenatal exposure to stress and alcohol may also play a role.
• Stress releases endorphins – antagonizes the effects of testosterone on the hypothalamus.
• Stress elevates adrenal hormone corticosterone – decreases testosterone release.
• Both result in changes in the structure of the nervous system.
– makes the male anatomy closer to female
Variations in Sexual Behavior
• Laboratory research has also shown that prenatal stress can alter sexual development.
• Male subjects subjected to either prenatal stress or alcohol developed male sexual behavior in addition to female sexual behaviors.
• Male subjects exposed to both stress and alcohol during prenatal development had decreased sexual behavior.
Variations in Sexual Behavior
• Research also suggests that certain brain structures differ in size between heterosexual and homosexual men and women.
• On average, the homosexual brain is shifted towards the opposite sex in some (but not all) ways.
• Studies emphasize the role of testosterone at certain times of development as certain areas of the brain have altered sensitivities to testosterone.