In my last post, I pointed out that testosterone fuels the reckless sexual and aggressive behavior of young men and other male vertebrates. Recent research is closing in on sex hormones (androgens as well as estrogens) playing a very similar role for women.

The female hormone estradiol (a key estrogen) plays a role in dominance communication and physical aggression among primates. Recent evidence suggests that it stokes competition amongst human females. Women with a high need for power have higher estradiol levels in their blood. What is more, their estradiol level increases when they "win" a contest with another woman that is actually manipulated by experimenters and remains elevated for a day. Estradiol declines when they lose.

So far, it seems that estradiol plays a similar role in the competitive interactions of women as testosterone plays for men. Yet, there is little evidence that high-estradiol women are more aggressive in the way that high-testosterone men tend to be. Their other distinguishing features are that they tend to be physically attractive, to have tempestuous romantic lives, and to be highly competitive with other women (what might be called the Marilyn Munroe effect).

Patchy though this evidence is, it paints an intriguing picture of women as being affected by estrogens (i.e., estradiol) in much the same way that men are affected by androgens (i.e., testosterone). Yet, there is more. In addition to being swayed by womanly hormones, women are also affected by testosterone. This is normally thought of as a masculine hormone because it is present in much higher levels in males but it is present in women as well and affects both their competitive interactions and their sexual motivation which might help to explain why female sexual motivation is so different in various countries (as described in an earlier post).

Testosterone and womanly passions
Testosterone also plays an important role in the competitive interactions of female mammals, including primates. Testosterone is naturally present in women, being produced by the adrenal gland. It serves many different functions apart from sexuality and aggression. These include the growth of pubic hair, muscle development, fat deposition around the waist, and the organization of brain circuitry before birth.

Women with high testosterone levels describe themselves as being action-oriented, resourceful and powerful. Effects on physical aggression are unclear. Research shows that high-testosterone women are more competitive and more verbally aggressive, however. In experiments, women administered testosterone respond more strongly to angry faces. They also take bigger risks in a game of chance. Women who had been exposed to more testosterone early in development (as inferred from the relative length of the ring finger compared to the index finger) are more competitive, more assertive, and more socially dominant. Testosterone affects sexual behavior in women as well as men.

Small doses of testosterone are used to treat extremely low levels of sexual desire in women that compromises their sexual function and threatens their marriages. Experiments have shown that testosterone administration increases self-rated genital sensitivity and objectively-measured sexual arousal in response to an erotic movie. On the other hand taking contraceptive pills, which render testosterone inactive by increasing the amount of sex hormone binding globulin, reduces sexual desire, interferes with lubrication, and decreases sexual enjoyment.

Although psychologists are often wary of acknowledging that hormones play much of a role in human psychology or behavior, the evidence suggests otherwise. Like robins in the springtime, young men are more amorous and more reckless, so that they are more likely to break rules, drive dangerously, and get in fights.

What is sauce for the gander turns out to be sauce for the goose. Women are more competitive, more risk-taking, and more socially dominant, if they are affected by high levels of sex hormones (both estradiol and testosterone). Surprisingly, the hormone that plays the clearest role in female social competition, and in feminine lust, is not an estrogen, but an androgen - testosterone.

These phenomena turn out to have many practical applications. For instance, women have higher testosterone levels in societies where they compete with each other in the work place. This means that they are more sexually liberated and behave more like men in relation to drug use, reckless conduct, and crime. Indeed, their body shape becomes more masculine. More on this in a later post.

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