Relationships/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, testosterone triggers production of sperm and growth of facial and body hair, as wells as causes deep voices, and muscle mass and strength.

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.

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

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. Testosterone injections do not increase sexual activity or sexual desire in young men. Men have more than enough testosterone for sex.

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

Men's hormone levels are also influenced by their partners. One study (Toronto, Ontario 2006) found that increases or decreases in men's levels of testosterone are often correlated to their wives' menstrual cycles: the husband's testosterone tends to increase when the wife is ovulating, and decrease again afterward. This effect was observed particularly in younger couples.

Testosterone in Women
Women have about one-tenth of men's testosterone.

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. 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. Alcoholism reduces sexual functioning in women, but not as severely as the effect in men.

Boost Your Testosterone Without Pills or Patches
To boost your testosterone:
 * Avoid alcohol, if you are a man.
 * Sexual activity increases testosterone, in both men and women.
 * 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 does not affect testosterone.
 * The presence of females, especially new females, boosts male testosterone. Speculatively, young women increase men's testosterone more than older women. You do not 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.
 * Follow workouts like sit and squats, bench press with stop bars, deadlifts with stop bars etc..

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. Diminishing testosterone does not sufficiently explain the declining sexual activity associated with aging.

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. 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. 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, female solicitations of males for sex, and male sexual performance.

Orgasms increase women's estrogen.

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

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

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

A variety of behaviors affect progesterone. Breastfeeding, oral contraceptives, and lack of exercise 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.

Sexual Peaks of the Menstrual Cycle
Estrogen, progesterone, and testosterone vary widely over women's 28-day menstrual cycles.

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."

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. 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.

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."

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

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

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).

Pheromones
Pheromones are chemicals in sweat and urine. Animals use pheromones to sense whether another animal is male or female, related or unrelated, 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. 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.

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 do not fight other male mice.

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.

Pheromones
Bacteria and fungi live on your skin and in your clothes. These organisms drink your sweat and digest your discarded skin cells, causing body odor.

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 does not 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, varies even more between men, and diminishes with age, but, compared to women, the male sex drive is relatively constant. In general, mens' sex drives are higher.

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.

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.

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.

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. 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.

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

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.

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. The adult women have masculine features, behavior, and sexual attraction to women.

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.