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"In recent years more and more evidence has been found that testosterone affects not just ornaments and bodies but also brains. Testosterone is an ancient chemical, found in much the same form throughout the vertebrates. Its concentration determines aggressiveness so exactly tht in birds with reversed sex roles, such as phalaropes and in female-dominated hyena clans, it is the females that have higher levels of testosterone in the blood. Testosterone masculinizes the body; without it, the body remains female, whatever its genes. It also masculinizes the brain. Among birds it is usually only the male that sings. A zebra finch will not sing unless there is suffecient testosterone in its blood. With testosterone, the special song-producing part of its brain grows larger and the bird begins to sing. Even a female zebra finch will sing as long as she has been exposed to testosterone early in life and as an adult. In other words, testosterone primes the young zebra finch's brain to be responsive later in life to testosterone again and so develop the tendency to sing. Insofar as a zebra finch can be said to have a mind, the hormone is a mind-altering drug. Much the same applies to human beings. Here the evidence comes from a series of natural and unnatural experiments. Nature has left some men and women with abnormal hormonal doses, and in the 1950's doctors changed the hormonal conditions of some wombs by injecting some pregnant women with certain hormones. Women with a condition known as Turner's syndrome (they are born without ovaries) have even less testosterone in their blood than do women who have ovaries. (Ovaries produce some testosterone, though not as much as testicles do.) They are exaggeratedly feminine in their behavior, with typically a special interest in babies, clothes, housekeeping, and romantic stories. Men with less than usual testosterone in their blood as adults---eunuchs, for example---are noted for their femininity of appearance and attitude. Men exposed to less than usual testosterone as embryos---for example, the sons of diabetic women who took female hormones during pregnancy---are shy, unassertive, and effeminate. Men with too much testosterone are pugnacious. Women whose mothers were injected with progesterone in the 1950's (to avert miscarriage) later described themselves as having been tomboys when young; progesterone is not unlike testosterone in its effects. Girls who were born with an unusual condition called either adrenogenital syndrome or congenital adrenal hyperplasia are equally tomboyish. This order causes the adrenal gland, near the kidney, to produce a hormone that acts like testosterone instead of cortisol, its usual product. Somewhat like in the zebra finches, there is two periods when testosterone levels rise in male children: in the womb, from about six weeks after conception, and at puberty. As Anne Moir and David Jessel put it in a recent book, Brain Sex, the first pulse of hormone exposes the photographic negative; the second develops it. This is a crucial difference fro the way the hormone affects the body. The body is masculinized by testosterone from the testicles at puberty, whatever its womb experience. But not the mind. The mind is immune to testosterone unless it was exposed to a sufficient concentration (relative to female hormones) in the womb. It would be easy to engineer a society with no sex difference in attitude between men and women. Inject all pregnant women with the right dose of hormones, and the result would be men and women with normal bodies but identical feminine brains. War, rape, boxing, car racing, pronography, and hambergers and beer would soon be distant memories. A feminist paradise would have arrived. (Ridley 1993: 254-6, The Red Queen)
"Yet at five the testosterone levels in the average boy are identical to those of the average girl, and a fraction of what they were at birth." (Ridley 1993: 258, The Red Queen)
"He now [at puberty] has twenty times as much of it [testosterone] in his blood as a girl of the same age." (Ridley 1993: 258, The Red Queen)
"You need some testosterone around for normal aggressive behavior---zero levels after castration, and down it usually goes; quadruple it (the sort of range generated in weight lifters abusing anabolic steroids), and aggression typically increases. But anywhere from roughly 20 percent of normal to twice normal and it's all the same; the brain can't distinguish among this wide range of basically normal values." (Sapolsky 1997: 154, TheTrouble With Testosterone)
"This is critical: testosterone isn't causing aggression, it's exagerating the aggression that's already there." (Sapolsky 1997: 155, TheTrouble With Testosterone)
"There is indeed some evidence that females who are high and males who are low in the male sex hormone (androgen) score higher on spatial ability tests (see McGee, 1979). While this would support the idea of the need for an optimal (i.e. intermediate) level of hormones...." (Bradshaw & Nettleton 1983: 218, Human Cerebral Asymmetry)
"When gonadectomized males were treated with testosterone, however, they became more aggresive to subordinate males but not to more dominant males or females. Factors such as physical condition and previous social experience may be more important than gonadal hormones in influencing aggresive interactions in these captive groups of talapoins." (Dixon, A. & Herbert, J. (1977) Testosterone, Aggressive Behavior and Dominance Rank in Captive Adult Male Talapoin Monkeys Physiology and Behavior 18: pp. 539)
http://www.neoteny.org/a/testosterone.html
"In recent years more and more evidence has been found that testosterone affects not just ornaments and bodies but also brains. Testosterone is an ancient chemical, found in much the same form throughout the vertebrates. Its concentration determines aggressiveness so exactly tht in birds with reversed sex roles, such as phalaropes and in female-dominated hyena clans, it is the females that have higher levels of testosterone in the blood. Testosterone masculinizes the body; without it, the body remains female, whatever its genes. It also masculinizes the brain. Among birds it is usually only the male that sings. A zebra finch will not sing unless there is suffecient testosterone in its blood. With testosterone, the special song-producing part of its brain grows larger and the bird begins to sing. Even a female zebra finch will sing as long as she has been exposed to testosterone early in life and as an adult. In other words, testosterone primes the young zebra finch's brain to be responsive later in life to testosterone again and so develop the tendency to sing. Insofar as a zebra finch can be said to have a mind, the hormone is a mind-altering drug. Much the same applies to human beings. Here the evidence comes from a series of natural and unnatural experiments. Nature has left some men and women with abnormal hormonal doses, and in the 1950's doctors changed the hormonal conditions of some wombs by injecting some pregnant women with certain hormones. Women with a condition known as Turner's syndrome (they are born without ovaries) have even less testosterone in their blood than do women who have ovaries. (Ovaries produce some testosterone, though not as much as testicles do.) They are exaggeratedly feminine in their behavior, with typically a special interest in babies, clothes, housekeeping, and romantic stories. Men with less than usual testosterone in their blood as adults---eunuchs, for example---are noted for their femininity of appearance and attitude. Men exposed to less than usual testosterone as embryos---for example, the sons of diabetic women who took female hormones during pregnancy---are shy, unassertive, and effeminate. Men with too much testosterone are pugnacious. Women whose mothers were injected with progesterone in the 1950's (to avert miscarriage) later described themselves as having been tomboys when young; progesterone is not unlike testosterone in its effects. Girls who were born with an unusual condition called either adrenogenital syndrome or congenital adrenal hyperplasia are equally tomboyish. This order causes the adrenal gland, near the kidney, to produce a hormone that acts like testosterone instead of cortisol, its usual product. Somewhat like in the zebra finches, there is two periods when testosterone levels rise in male children: in the womb, from about six weeks after conception, and at puberty. As Anne Moir and David Jessel put it in a recent book, Brain Sex, the first pulse of hormone exposes the photographic negative; the second develops it. This is a crucial difference fro the way the hormone affects the body. The body is masculinized by testosterone from the testicles at puberty, whatever its womb experience. But not the mind. The mind is immune to testosterone unless it was exposed to a sufficient concentration (relative to female hormones) in the womb. It would be easy to engineer a society with no sex difference in attitude between men and women. Inject all pregnant women with the right dose of hormones, and the result would be men and women with normal bodies but identical feminine brains. War, rape, boxing, car racing, pronography, and hambergers and beer would soon be distant memories. A feminist paradise would have arrived. (Ridley 1993: 254-6, The Red Queen)
"Yet at five the testosterone levels in the average boy are identical to those of the average girl, and a fraction of what they were at birth." (Ridley 1993: 258, The Red Queen)
"He now [at puberty] has twenty times as much of it [testosterone] in his blood as a girl of the same age." (Ridley 1993: 258, The Red Queen)
"You need some testosterone around for normal aggressive behavior---zero levels after castration, and down it usually goes; quadruple it (the sort of range generated in weight lifters abusing anabolic steroids), and aggression typically increases. But anywhere from roughly 20 percent of normal to twice normal and it's all the same; the brain can't distinguish among this wide range of basically normal values." (Sapolsky 1997: 154, TheTrouble With Testosterone)
"This is critical: testosterone isn't causing aggression, it's exagerating the aggression that's already there." (Sapolsky 1997: 155, TheTrouble With Testosterone)
"There is indeed some evidence that females who are high and males who are low in the male sex hormone (androgen) score higher on spatial ability tests (see McGee, 1979). While this would support the idea of the need for an optimal (i.e. intermediate) level of hormones...." (Bradshaw & Nettleton 1983: 218, Human Cerebral Asymmetry)
"When gonadectomized males were treated with testosterone, however, they became more aggresive to subordinate males but not to more dominant males or females. Factors such as physical condition and previous social experience may be more important than gonadal hormones in influencing aggresive interactions in these captive groups of talapoins." (Dixon, A. & Herbert, J. (1977) Testosterone, Aggressive Behavior and Dominance Rank in Captive Adult Male Talapoin Monkeys Physiology and Behavior 18: pp. 539)
