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Hormones

Testosterone Testosterone is a hormone produced primarily in men's testes. The adrenal glands of both men and women also produce small amounts of testosterone. In men, test...
Views: 9.342 Created 01/12/2007

Testosterone

Testosterone is a hormone produced primarily in men's testes. The adrenal glands of both men and women also produce small amounts of testosterone.[1]

In men, testosterone produces sperm, facial and body hair, deep voices, and muscle mass and strength.[2]

Testosterone is associated with two behaviors in males: aggressive dominance of other males, and sexual activity. E.g., male red deer live peacefully together for most of the year. But in October their testosterone increases five-fold. They fight for territory. Female red deer select land that has sufficient food for raising fawns. The males that control the best territories mate with the most females.[3]

Testosterone is an anti-depressant, in men and women.[4] It increases friendliness. It reduces anger, depression, fatigue, confusion, nervousness, and irritability.[5]

That may seem contradictory-testosterone makes males fight, yet makes them friendly. Testosterone makes males want to mate. If fighting precedes mating--e.g., gorillas--testosterone makes males fight. But if mating requires friendship-e.g., baboons- testosterone makes males friendly.

Testosterone and Sexual Behavior

Testosterone is necessary for sexual activity. However, the amount of testosterone needed for sexual activity is low.[6] Testosterone injections don't increase sexual activity or sexual desire in young men.[7] Men have more than enough testosterone for sex.

Who Has the Most Testosterone?

Testosterone varies between men more than four times.[8] Football players have the most testosterone. Ministers have the least.[9]

Men and women with high testosterone commit more violent crimes. They're more unruly in prison. Parole boards judge them more harshly.[10]

Bachelors have more testosterone than married men. Childless husbands have more testosterone than fathers.[11] Low testosterone in men correlates with marital satisfaction. Low testosterone improves emotional expressiveness, parent-child communication, and "androgynous behaviors"-the ability to use feminine skills when necessary.[12]

Testosterone in Women

Women have about one-tenth of men's testosterone.[13]

Women's sexuality requires testosterone.[14] Women with more testosterone have less depression, more sexual enjoyment, better interpersonal relationships, and happier marriages.[15] Happy marriages consist of high-testosterone women and low-testosterone men.

Female executives and attorneys have more testosterone than secretaries, teachers, nurses, and housewives.[16]

Women who don't use condoms are less depressed than women who use condoms, or who aren't sexually active. Women who don't use condoms become increasingly depressed as time elapses since their last sexual encounter. They also seek new partners sooner after ending a relationship. Women apparently absorb an anti-depressant hormone, possibly testosterone, from semen.[17]

If you're a depressed woman, talk to your doctor about trying a low dosage of testosterone instead of Prozac or other anti-depressants.

Alcohol and Testosterone

Alcohol lowers men's testosterone. Liver damage (associated with alcoholism) increases clearance of testosterone from the blood, and decreases clearance of estrogen.[18] Increased estrogen and decreased testosterone reduce the functioning of men's testes.

Alcohol has no effect on the hormones of healthy non-alcoholic young women.[19] Alcoholism reduces sexual functioning in women, but not as severely as the effect in men.[20]

Boost Your Testosterone Without Pills or Patches

To boost your testosterone:

  • Avoid alcohol, if you're a man.
  • Sexual activity increases testosterone, in both men and women.[21]
  • Winning boosts testosterone. Losing reduces testosterone. Find a sport you can win at, e.g., softball vs. baseball. You have to win at something physical and indicative of social dominance, e.g., winning the lottery doesn't affect testosterone.[22]
  • The presence of females, especially new females, boosts male testosterone.[23] Speculatively, young women increase men's testosterone more than older women. You don't need to have sex to get this effect. The effect is produced via pheromones in women's sweat. Play a sport you can win, on a team with sweating young women.

Testosterone and Aging

Pre-pubescent boys have little testosterone. After puberty, testosterone increases in teenagers. Testosterone is generally stable until men are in their 60s. Testosterone then decreases in old age.[24] Diminishing testosterone doesn't sufficiently explain the declining sexual activity associated with aging.[25]

A study in the United States, Congo, Nepal, and Paraguay found that Americans have the highest testosterone when young, and the least in old age, but testosterone levels are nearly constant from adolescence to old age in traditional societies in the other three countries.[26] This difference may be due to how American men and women interact. North American young men interact with many young women, in high school and college. Older American men, however, have interaction with far fewer non-related young women. In rural societies in many other countries, by contrast, men generally interact with roughly the same number of young women throughout their adult lives.

Estrogen and Progesterone

Women's ovaries produce estrogen and progesterone.[27] Estrogen increases in girls at puberty, making them develop breasts and hips. Estrogen drops at menopause (around age 50).

Estrogen is associated with ovulation and sexual receptivity. In female animals, estrogen increases male interest in the female,[28] female solicitations of males for sex,[29] and male sexual performance.[30]

Orgasms increase women's estrogen.[31]

Progesterone

Progesterone is associated with pregnancy, nursing, and other nonfertile states.[32]

Progesterone reduces female sexual behavior.[33] It inhibits orgasm.[34] It causes mild depression.[35] Prisons use a form of progesterone to "chemically castrate" male sex offenders.[36]

Progesterone increases maternal behavior. E.g., progesterone causes female rabbits to build nests.[37] Progesterone causes maternal aggression toward animals that approach a mother's young.[38]

A variety of behaviors affect progesterone. Breastfeeding,[39] oral contraceptives,[40] and lack of exercise[41] increase progesterone-and reduce sex drive.

Increased progesterone may be a factor in the 70% average drop in marital satisfaction in the first few years after the birth of a couple's first child.[42]

Sexual Peaks of the Menstrual Cycle

Estrogen, progesterone, and testosterone vary widely over women's 28-day menstrual cycles (see Figure 2: Hormones Over Menstrual Cycle).

For the first 10-12 days after menstrual bleeding ceases, estrogen and testosterone are low but increasing. Progesterone is very low. A woman described this time as "confident and social, on the prowl."[43]

Women ovulate around days 13-15. Estrogen and testosterone peak. Progesterone remains low. Brain scans show that women respond more dramatically to pictures of nude men during ovulation.[44] Sexual behavior peaks. Ovulating women in singles bars wear, on average, more jewelry and makeup than they do at other times of the month, according to Australian research. They are more likely to initiate physical contact with men.[45]

During the two weeks after ovulation, progesterone dominates. Estrogen remains moderately high. Testosterone diminishes. Progesterone makes women not want sex, but feel nurturing. A woman described this time as "too tired for an orgasm, but could have touched all night."[46]

Progesterone and estrogen drop a few days before menstruation. This relates to premenstrual syndrome (PMS) in some women.[47]

Image:Hormones Over Menstrual Cycle
Figure 2: Hormones Over Menstrual Cycle

A man reading that might think, "If I knew when women were ovulating, dating would be much easier!" Indeed, females of almost all other species show males when they're ovulating. Many species are physically incapable of intercourse when the female isn't ovulating.

But ovulation is relatively concealed, rather than obvious. (If they didn't, some men would date them when they were ovulating, and date other women the rest of the month.)

If a man doesn't know when his wife is fertile, he must have sex with her throughout the month to father a child--or each day stop her from having sex with other men, to prevent other men from getting her pregnant.

Oxytocin

The pituitary gland (in the brain) produces oxytocin. Both males and females produce oxytocin. Oxytocin is unique to mammals.

Affectionate touching releases oxytocin. Cuddling a child or pet is pleasurable because of oxytocin. An infant suckling releases the mother's oxytocin, making nursing pleasurable for women.

Individuals who regularly cuddle can become addicted to each other. They can experience oxytocin withdrawal when apart.[48]

Oxytocin releases cyclically. Couples reach the highest levels of sexual feeling by alternating about twenty minutes of intense touching with relaxation or less intense touching.

Orgasm spikes oxytocin to five times normal levels. The refractory or disinterested period some people feel after sex may be due in part to oxytocin overdose (too much of any drug reduces sexual interest).[49] Test this hypothesis by cuddling more when you're not having sex, to get your brain used to oxytocin.[50]

Pheromones

Pheromones are chemicals in sweat and urine. Animals use pheromones to sense whether another animal is male or female, related or unrelated,[51] sexual receptiveness in females, and dominance in males. The vomeronasal organ (VNO) in the nose detects pheromones. The VNO is distinct from the nose's smell faculty-pheromones are a "sixth" sense. Many scientists believe that the VNO in humans merges into the sinus during fetal development, and that many people do not have a functional VNO.

The VNO connects to the accessory olfactory bulb, which is a brain area distinct from the main olfactory bulb (which processes our sense of smell). From there, pheromone information goes directly to the reptilian brain, and the limbic (old mammalian) brain area for maternal behavior. Pheromone information never gets to our cerebral cortex, the recently evolved brain area for consciousness and abstract thinking.[52] We have no conscious awareness of pheromones.

Exposure to male perspiration brightens women's moods, reduces tension and increases relaxation. It is also theorized that male perspiration slightly affects women's menstrual cycle timing.[53]

Exposure to men's sweat can make other men feel weak or subordinate. To maintain your self-esteem, avoid getting too close to other men or their clothes (e.g., when flying coach).

Male mice missing the pheromone receptor gene are unable to sense "maleness" in other mice. These male mice treat all other mice as female. They try to mate with male mice as well as with female mice. They don't fight other male mice.[54]

Major Histocompatibility Complex Molecules

Parents with genetically different immune systems produce offspring with strong immune systems. Parents with genetically similar immune systems can be infertile or have miscarriages. Females sense a male's immune system via major histocompatibility complex (MHC) molecules. The VNO appears to sense MHC.

The sweat of men with genetically different MHC attracts women. The sweat of men with genetically similar MHC repulses women.

Pregnant female mice seek males with genetically similar MHC. These males are likely to be relatives and will protect their baby relations.[55]

Pheromones Are Not Body Odor

Bacteria and fungi live on your skin and in your clothes. These organisms drink your sweat and digest your discarded skin cells. Their excretions make you smell disgusting. That's body odor.[56]

Women's sense of smell (olfactory sensitivity) is, on average, better than men's. Ask a woman if you smell bad. If so, shower with antibacterial soap. If that doesn't eliminate body odor, shave your body hair (especially your armpits), shave your beard, and get a haircut. Hair holds body odor.

Conversely, if women like your smell, grow a beard and long hair, and keep your body hair.

But frequent showering also washes away your pheromones. To attract women, men need pheromones without body odor. Contrary to spam e-mail advertisements, you can't buy human sexual pheromone colognes. Don't be afraid to sweat on a date, if you've gotten rid of skin bacteria.

(Perhaps we're actually offended by pheromones, not body odor. What if I had to negotiate a business deal with a man who makes me feel weak and queasy? What if I had to work next to a woman who makes me unable to think about anything but sex? Perhaps we shower daily and use anti-perspirants so that we can get along with each other.)

Do Men and Women Have Different Sex Drives?

Men's sex drive results from one hormone. Testosterone varies 50% or more daily,[57] varies even more between men, and diminishes with age, but, compared to women, the male sex drive is relatively constant. In general, men are ready for sex anytime, anywhere.

In contrast, three hormones-estrogen, progesterone, and testosterone-control women's sex drive. Women's interest in sex varies in character and intensity over their menstrual cycles, during pregnancy and nursing, and during menopause. Women's sex drives can be as strong or stronger than men's, but only at specific times.

Female mammals will have sex only in certain places. E.g., female elephant seals select a beach with minimal danger from predators. Female red deer select a meadow with abundant food to support fawns. Many human females like familiar surroundings, moderate temperature, etc.

Female primates prefer to mate with specific males. Whether a male physically dominated other males (e.g., gorillas), or built a social network (e.g., baboons), or is one's life partner (e.g., gibbons), rejecting inappropriate males is central to female sexuality.

Fetal Testosterone and Brain Differences

Foeti are of "indifferent" sex for the first six weeks. Foeti with XY (male) chromosomes then produce testosterone. Testosterone causes the XY fetus to develop male genitalia and physique.

XY foeti convert some of the testosterone into estrogen. Estrogen masculinizes a fetus.[58]

XX (female) foeti are normally not exposed to testosterone or estrogen. They develop female organs, and feminine features and behavior.

Cognitive Differences

Women generally have better senses of smell, taste, and hearing. Men generally have better vision.[59]

Women often have better verbal skills. In general, they have better fine motor skills, e.g., threading a needle or connecting small wires. Men are often better at "directed motor skills," e.g., throwing a ball, and "visual-spatial abilities," e.g., map reading and mental rotation of 3-D objects.[60]

70% of men tend to use one brain hemisphere at a time while working on a task. Men can often concentrate on a task for long periods.[61] Focusing on an activity without distractions soothes men, e.g., driving a motorcycle across the country.

Most women multi-task, e.g., minding a baby while cooking dinner while talking on the telephone. Approximately 70% of women (as opposed to 35% of men) are adept at multitasking, according to one study. So-called "woman's intuition" (HSI, as it is more technically called) results from using her whole brain to solve a problem.

Abnormal Fetal Testosterone

XX (female) foeti exposed to testosterone develop masculinized features, e.g., a clitoris as large as a small penis, and (sometimes) masculine thinking patterns and behaviors. Conversely, XY (male) foeti not exposed to testosterone become feminized.[62]

Switching the hormones of baby animals-rats, ferrets, pigs, finches, and monkeys[63] - makes males grow up to behave as females, and vice versa.[64] Females attempt to mount females. Males assume the lordosis female sexual posture to get males to mount them.[65] Given a choice of male or female sexual partners, the hormonally manipulated animals choose their own sex.[66]

Stressing pregnant rats (e.g., forcing them to remain immobile in bright light, which terrifies normally nocturnal animals) causes them to produce homosexual or bisexual male offspring.[67]

Some genetic disorders and hormone imbalances expose human XX (female) foeti to testosterone or estrogen, or prevent testosterone exposure of XY (male) foeti. These XY (male) adults look and act like women (sometimes including sexual attraction to men). The XX (female) girls prefer to play with trucks instead of dolls.[68] The adult women have masculine features, behavior, and sexual attraction to women.[69]

Gender identity, sexual biology, and cognitive skills appear to develop at different stages of pregnancy. Abnormal fetal hormones at certain points in pregnancy can produce one gender abnormality, while the individual otherwise develops normally. E.g., a man could think of himself as masculine, wear men's clothing, etc., but feel sexual attraction to other men.[70]

Abnormal fetal testosterone can be a gift. Normal men and women can get stuck in masculine or feminine thinking patterns. Too often men can't understand women, and women can't understand men. But, as in the saying "two heads are better than one," individuals with androgynous tendencies can solve problems that stump other men and women.[71] They can use masculine aggressiveness and goal-orientation. They can use feminine listening, verbal, and social skills. For example, gays and lesbians can be adept diplomats--or spies.

Content by Wikibooks . Text is available under the terms of the GNU Free Documentation License

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