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Ppt Chap 11 Presentation Transcript

  • 1. Chapter 11: Reproductive Behaviors
  • 2. 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.
  • 3. Sex and Hormones
    • Widespread communication throughout the body is accomplished through the release of hormones.
    • Two kinds of hormones include:
      • Steroid hormones
      • Sex hormones
  • 4. Sex and Hormones
    • Steroid hormones are derived from cholesterol, contain four carbon rings and exert their effects in three ways.
      • Binding to membrane receptors like neurotransmitters.
      • Entering cells and activate certain kinds of proteins in the cytoplasm.
      • Binding to chromosomes where they activate or inactivate certain genes.
  • 5.  
  • 6.  
  • 7. 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:
      • Androgens
      • Estrogens
    • Both sexes have these categories in varying quantities .
  • 8. 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.
  • 9. 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.
  • 10. 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
  • 11. Sex and Hormones
    • Sex hormones can have the following effects:
    • Organizing effects- occur mostly at sensitive stages of development.
      • -Determine whether the brain and body will develop male or female characteristics
    • Activating effects- occur at any time of life and temporarily activate a particular response.
  • 12. 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
  • 13. 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 and a set of Wolffian ducts as well as primitive gonads.
  • 14. 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.
  • 15. 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.
  • 16. 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 month of pregnancy.
  • 17.  
  • 18. 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
  • 19. 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.
  • 20. 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.
  • 21. Sex and Hormones
    • During early development in rodents, testosterone is converted within certain brain cells to estradiol, which masculinizes development.
    • Alpha-fetoprotein is found in the blood during early sensitive periods and binds to estrogen and prevents it from entering developing cells.
    • Testosterone does not bind to alpha-fetoprotein and freely enters the cell.
  • 22. 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.
  • 23. 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.
  • 24. Sex and Hormones
    • Sex hormones also increase responses of certain areas of the hypothalamus.
      • the ventromedial nucleus, the medial preoptic area (MPOA), and the anterior hypothalamus.
    • Stimulation of an area known as the sexually dimorphic nucleus (SDN) fpound in the anterior hypothalamus is larger in males and increases sexual behavior in males of many species.
  • 25. 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 receptors is associated with sexual arousal.
      • 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.
  • 26. 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.
  • 27. Sex and Hormones
    • Decreases in testosterone levels generally decrease male sexual activity and interest.
      • Example: castration
    • Impotence is the inability to maintain an erection.
      • 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.
  • 28. 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.
  • 29. Sex and Hormones
    • In women, the hypothalamus and pituitary interact with the ovaries to produce the menstrual cycle.
    • The menstrual cycle is the periodic variation in hormones and fertility over the course of about 28 days.
  • 30. 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.
  • 31.  
  • 32. 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
  • 33.  
  • 34. 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.
  • 35. 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.
  • 36. 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.
  • 37. 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
  • 38. 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.
  • 39. 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.
  • 40.  
  • 41. 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.
  • 42.  
  • 43. Sex and Hormones
    • Mammals have two mechanisms for stimulating maternal behavior:
      • Hormones in the early phase compensate for the lack of familiarity with the young.
      • 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.
  • 44. 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.
  • 45. 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.
  • 46. 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.
  • 47. 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.
  • 48. 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.
  • 49. 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.
  • 50. 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.
  • 51. 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.
  • 52. 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”.
  • 53. 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.
  • 54. 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.
  • 55.  
  • 56. 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.
  • 57. 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.
  • 58. 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.
  • 59.  
  • 60. 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.
  • 61. 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.
  • 62. 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.
  • 63. 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.
  • 64. 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.
  • 65. 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.
  • 66. 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.
  • 67.  
  • 68. 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.
  • 69. 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.
  • 70. 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.
  • 71. Variations in Sexual Behavior
    • Sexual orientation is not related to adult hormone levels.
    • May be influenced by exposure to testosterone during sensitive periods.
  • 72. 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.
  • 73. 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
  • 74. 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.
  • 75. 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.
  • 76. Variations in Sexual Behavior
    • On average, differences in brain anatomy exist between heterosexual and homosexuals.
    • Homosexual men tend to have:
      • Larger anterior commissure and suprachiasmatic nucleus
      • Smaller neurons in the third interstitial nucleus of the anterior hypothalamus (INAH-3)
    • Difficult to decipher why differences exist.
  • 77.  
  • 78.  
  • 79.