PHYSIOLOGICAL PSYCHOLOGY

• Children


  • Begin to prefer sex-typed toys between the ages of 12 and 18 months
• Young male monkeys


  • Spend more time with wheeled toys and balls
• Young female monkeys


  • Prefer dolls, plush animals, and pots
• These results suggest that at least part of the preference we see in toy selection among boys and girls may originate in biology
• Aristotle argued that the sex of a child was the result of the temperature of semen at the time of conception

  355 B.C.
• Genetic sex


  Begins with sex chromosomes inherited from two parents
• Mothers provide an X chromosome to all their offspring; fathers determine the offspring's sex by providing either another X (producing a female) or a Y chromosome (producing a male)
• The initial XX or an XY genotype begins a cascade of hormonal, structural, and behavioral events
• Maleness and femaleness often viewed inaccurately as distinct and separate categories
• The fetus is initially undifferentiated regarding sex
• Without exposure to male hormones, all babies would be born with outwardly female appearance and behavior
• Male and female structural development

  1. Development of gonads

  2. Development of internal organs

  3. Development of external genitalia
• Intersex


  A rare condition where elements of both male and female development occur in the same fetus
• Development of Gonads


  1. Up until the sixth week after conception, both male and female fetuses have identical primordial gonads

  2. At about six weeks after conception, a gene on the short arm of the Y chromosome, known as the sex-determining region of the Y chromosome, or SRY, is expressed in male embryos

  3. Testis-determining factor, the protein encoded by the SRY gene, switches on additional genes that cause the primordial gonads to develop into testes

  4. In female embryos, which lack the SRY gene and its ability to produce testis-determining factor, alternate genes guide the development of the primordial gonad into ovaries
• Differentiation of the Internal Organs


  1. Until about the third month of development in humans, both male and female fetuses possess a male Wolffian system and a female Müllerian system

  2. In males, the Wolffian system will develop into the seminal vesicles, the vas deferens, and the prostate. In females, the Müllerian system will develop into the uterus, the upper portion of the vagina, and the fallopian tubes

  3. During the third month, the male's relatively new testes begin to secrete two hormones, testosterone, and anti-Müllerian hormone

  4. Testosterone promotes the development of the Wolffian system

  5. Anti-Müllerian Hormone initiates the degeneration of the Müllerian system

  6. In the absence of any androgens or anti-Müllerian hormone, the Müllerian system will develop in the typical female direction
• Development of the External Genitalia

  1. The male external genitalia includes the penis and scrotum. The female external genitalia includes the labia, clitoris, and outer part of the vagina

  2. No hormonal activity is required to develop female external genitalia. However, hormonal stimulation is essential for the development of male external genitalia

  3. A particular androgen, 5-alpha-dihydrotestosterone, must be recognized by receptor sites for the male external genitalia to develop naturally

  4. A reaction between testosterone from the testes and the enzyme 5-alpha-reductase produces 5-alpha-dihydrotestosterone

  5. Absence of 5-alpha-dihydrotestosterone leads the immature genitalia to develop in the female pattern
• Secondary sex characteristics


  • Facial hair and a more resonant voice for males
  • Broader hips and breast development for females
• The average age of puberty has dropped dramatically over the past century and a half, from about 16 to about 12 years of age
• Possible explanations for the drop in age at puberty

  • Increased rates of obesity
  • Exposure to compounds like female hormones in meat and dairy products, shampoo, plastics, and insecticides
• All edible tissues from animals contain a type of estrogen, or female hormone, called estradiol, so we can assume that humans have always experienced some level of exposure to outside sources of sex hormones
• Phthalates, compounds frequently found in plastics and cosmetics, have been found to advance puberty in rats
• Sex hormones


  Organize circuits in the brain that differ according to sex in prenatal and early postnatal development, and are then activated by the sex hormones at the onset of puberty
• Sex hormones


  Classified as steroids, chemicals that are synthesized from cholesterol in the gonads and lesser amounts, in the adrenal glands
• Males and females both produce androgens and estrogens, but in different amounts
• Females produce about 10 percent of the number of androgens produced by males
• Regulation of Sex Hormones by the Hypothalamus and Pituitary Gland

  1. The hypothalamus exerts control over the release of sex hormones through its secretion of gonadotropin-releasing hormone (GnRH)

  2. Light sensed by the retina increases GnRH secretion through its action on melatonin, a neurohormone implicated in the regulation of sleep and produced by the nearby pineal gland

  3. Melatonin inhibits the release of GnRH typically, and light, in turn, inhibits melatonin which is secreted primarily at night

  4. Light, therefore, increases GnRH release by reducing the inhibition usually produced by melatonin
• Estrus


  A period of hours or days in which the female is receptive to males
• Estrus coincides with ovulation in many species, making the likelihood of fertilization relatively high
• Only humans and Old-World primates experience menstrual cycles, and their sexual activity is quite different from species that have seasonal mating patterns or estrus
• Human females show receptivity throughout the menstrual cycle. However, some women report feeling slightly more interest in sex around the time of ovulation
• A woman's testosterone levels have the most significant impact on her sexual activity
• Women who receive standard estrogen replacement therapy following the surgical removal of their ovaries still report less satisfaction with their sex lives than before surgery
• After the women were given testosterone through a skin patch, they reported having sex more frequently and enjoying it more
• These hormonal effects are consistent with the observation that males have a slight advantage in spatial tasks, whereas females have a slight advantage in verbal tasks
• Estrogens have a protective effect on memory in general, and verbal memory, in postmenopausal women
• Estrogen replacement therapy (ERT), particularly in the few years immediately following menopause, helps prevent later cognitive decline
• Women were given testosterone through a skin patch


  They reported having sex more frequently and enjoying it more
• Women's testosterone levels were high

  They received their best scores on tests of mental figure rotations
• Women's estrogen levels were high

  They received their worst scores on tests of mental figure rotations
• Women's verbal fluency and manual dexterity

  Correlated with higher levels of estrogens