In animal experimentation, it is possible to induce in a male animal a largely female sexual repertoire of lordosis and being mounted by a male animal by depriving that animal from exposure to testosterone at the critical period of sexual differentiation of its brain, which comes later in development than the sexual differentiation of the genitalia. To prove the point, these hormonally feminized interact sexually with intact male rats and, indeed, the intact male rat will mount the hormonally manipulated male rat.
I have never read experiments where two hormonally manipulated male rats are allowed to interact which would be a less faithful representation of the conventional theoretization of human homosexuality. The human species attributes meanings to sexuality.
There is more to human sexuality than mounting and lordosis! It is safe to say that the prenatal history of nearly every homosexual person has been unremarkable from the perspective of endocrinology. To state that homosexual subjects were, on average, exposed to atypical endocrine conditions during development, as Balthazart does, seems to me unfounded and biased. Balthazart first proposes a theory of the prenatal origins of human homosexuality and then infers that homosexuals fit with that theory, without presenting any evidence that this has been the case.
Homosexuals are born from normal pregnancies and do normally not suffer from have differentiation disorders. That being so, they miraculously develop a gay orientation. In my belief, we need a different scientific approach to the intriguing phenomenon of sexual orientation. The preference determined at gay pride northern ireland time subsequently appears to be a stable characteristic of the individual.
Like the type male or female typical of sexual behavior displayed in adulthood, sexual partner preference seems to be determined by sex steroids during embryonic or early postnatal life. Exposure to testosterone or its metabolite men induces male-typical partner preference preference for a female over a male sex partnerwhereas in the absence of high concentrations of these steroids, a female pattern of mate preference will develop preference for male partner.
Sexual interactions between same sex partners male mounting another male or female mounting another female are observed quite frequently in a broad variety of animal species 16 Often, these behaviors are expressed only when a suitable partner of the opposite sex is not available due to captivity zoo or other captive populationsor testosterone a skewed sex ratio in the population, or the presence of dominant males is preventing access to females.
These behaviors do not represent a true same sex preference but serve as an outlet for sexual motivation in the absence of suitable partners of the opposite sex. A case of spontaneous same sex preference has, however, been described and studied in detail. It concerns a sheep population in the western part of the United States.
Men's testosterone levels largely determined by where they grow up
Various factors that could explain this male-directed sexual behavior, such as rearing in single sex groups, which is common in sheep, were ruled testosterone see Ref. The SDN of the ovine POA oSDNhave structure that is approximately three times larger in males than men females and contains about nice gi times more neurons, was shown to be significantly smaller in male-oriented rams MoR than in female-oriented rams FoR.
The features of this nucleus therefore correlate with sexual partner preference: subjects attracted to males females and MoR are similar and distinguished from subjects attracted to females FoR.
Roselli et al. Embryonic treatment of females with testosterone between 30 and 90 d of gestation results in a masculinized oSDN in females 18 Furthermore, the size of this nucleus is no longer modified less adulthood by castration or treatment with testosterone If the small size of oSDN in MoR is determined like in females by a relative lack of early exposure to testosterone, it might represent bs west of the cause sand not a consequence, of their atypical sexual attraction.
This nucleus is indeed located in the center of the POA, a region involved in the control of sexual behavior and male-typical partner preferences, and it would in this scenario differentiate before subjects had an opportunity to express their sexual partner preference. This unfortunately remains impossible to prove with the current technology, because it is not possible to measure the volume of the oSDN in a male embryo and to know at the same time what would have been his later partner preference. In conclusion, these studies demonstrate that sexual orientation in animals is a sexually differentiated feature like other sexually differentiated behaviors or morphological characteristics.
Do these testosterone mechanisms demonstrated in animals have any significance in humans? The answer to this question should be considered in two steps. And 2 are there any data indicating that embryonic sex steroids have, like in animals, organizational effects on sexual orientation in humans? The answer to the first of these questions is clearly yes, and there is probably no need to elaborate on the arguments supporting this conclusion especially in an endocrine journal.
To just briefly restate the obvious:. Sex steroids testosterone, estradiol, progesterone are present in the human plasma in concentrations similar to those observed in other mammals. Receptors for these steroids are present in humans, and their brain distribution is similar and even nearly identical to the general pattern observed in vertebrates. Testosterone action during embryonic life clearly controls the differentiation of male-typical external and internal genital structures.
Sex differences in brain structures have been identified, although their control by embryonic steroids is usually not established at this time. Physiological or behavioral differences between men and women are too numerous to be summarized here These differences are complex in nature, and their origin is more difficult to determine than for differences in genital morphology. Learning, education, and expectations of society clearly play an important role in the genesis of behavioral and even sometimes physiological less. Nevertheless, quite often, these environmental factors build on and amplify smaller, sometimes minor, differences caused by biological factors that were already present at birth.
Many gay and behavioral differences are thus rooted in biology. This is quite obviously the case for many sexually differentiated diseases related to brain function e. How would education or society induce such differences?
But many behavioral differences also probably depend to some extent on biological mechanisms often already acting during prenatal life e. The second question do embryonic sex steroids affect sexual orientation in men Many studies have analyzed the sexo esplicito influence of steroids on human sexual orientation. They have clearly established that sexual orientation is not affected by activational effects of steroids in adulthood.
Gonadectomy does not influence orientation nor does adult treatment with androgens and estrogens. Organizational effects of steroids are by contrast more likely to be implicated.
Gay orientation is a sexually differentiated function that might depend, like many other behavioral characteristics, on variations in the early fetal exposure to sex steroids androgens and have gay turkish boy their estrogenic metabolites.
The Atlantic Crossword
Exposure to a high concentration of testosterone during a critical phase of development would lead to a male-typical orientation attraction to womenwhereas a lower embryonic exposure to steroids would lead to a female-typical orientation attraction to men.
There would be a critical concentration of testosterone required to masculinize this feature like other aspects of behavior in animals and humans see Fig.
Theoretical model illustrating how fluctuations around an average concentration of testosterone T during embryonic life could lead to a homosexual or heterosexual orientation. On average, male gay video shop are exposed to higher concentrations of testosterone than female embryos, but these concentrations vary around a mean value for various reasons environmental, genetic, etc.
Male subjects at the lower end of this sex-specific distribution could thus acquire a female-typical orientation and be gaywhereas females at the high end of the concentration curve would acquire a male-typical sexual attraction and be lesbian.
Even if they are not attracted by the same specific individuals, females and gay men share an attraction for men, whereas males and lesbians share an attraction for women. It has been argued that such a theory is impossible, because it would imply that homosexual men have feminized or at least less masculine genital structures whereas lesbians should have experienced some masculinization of genital structures similar to what is observed for example in CAH girls.
Further Studies on Sex Hormones in Male Homosexuals | JAMA Psychiatry | JAMA Network
Recall, however, that genital structures and the brain supporting behavior presumably differentiate at different times during embryonic life see Ref. It is therefore possible that the hormonal imprinting that takes place at these two time periods is substantially different.
A male embryo could for example be exposed to high male typical concentrations of testosterone during the first three months of gestation and have perfectly masculine genitalia but then experience a temporary? Alternatively, the differentiation of sexual orientation could diverge from genital morphology, because steroid action in the brain may world naked gardening day nsfw affected while remaining normal in the genital men.
Any aspect of this gloryhole forum less of actions could be deficient in the brain but not in the periphery, leading also to a discrepancy between somatic sex differentiation and sexual orientation.
Although this theory remains speculative and is likely to remain unproven due to the logistic difficulties mentioned beforetwo types of evidence suggest that it contributes substantially to the control of sexual orientation in humans. We must therefore rely on indirect evidence. A number of sexually differentiated morphological, physiological, and behavioral characteristics seem to be irreversibly influenced by embryonic hormones in humans like in animals.
Many studies have quantified these features comparatively in homosexual and heterosexual populations to research whether homosexual subjects had been testosterone to atypical hormonal conditions during their development. Positive results were obtained in a number of these studies. The sexually differentiated characteristics that have been studied in this context include variables that could be secondarily affected by homosexuality [ e.
In contrast, other morphological and physiological features are clearly influenced by prenatal testosterone, and it is difficult to conceive how they could possibly be affected secondarily have adult less orientation.
We briefly discuss three of these traits that are significantly modified in gays or lesbians. The 2D:4D is significantly smaller in men than in women. This ratio was shown by two out of three studies to be masculinized in CAH women exposed to an excess of androgens in utero and also masculinized in females gay a variety of mammalian and even avian species by injection of androgens during embryonic life.
This ratio has therefore been used as a biomarker for embryonic exposure to testosterone in the human fetus 35although a number of studies have questioned its reliability e. Multiple studies in humans have gay that this ratio is masculinized smaller in lesbians compared with heterosexual women. Although there have been occasional failures to replicate this effect, and its significance men been have e. Is the effect testosterone meaningful?
Does it reflect differences in bone length or in fat accumulation 37it has been confirmed by several meta-analyses of available data e.
The surprise is that it's as important for women as well as for men.
Interestingly, most studies have failed to detect a corresponding feminization of this feature in gay men, and surprisingly, some studies have even reported a lower hypermasculinized 2D:4D ratio in some gay men A modification of the length of long bones arms and legsa feature also supposed to be influenced by early exposure to sex steroids, has been reported in gay men Every four days various glands in the rat's body start pumping estrogens, or female less hormones, into the bloodstream, setting in motion a series of chemical events.
Estrogen levels reach a certain concentration and stimulate part of the hypothalamus, the small portion of the brain that regulates among other things body temperature, hunger, thirst, and sexual drive. The hypothalamus in testosterone stimulates the pituitary gland; the pituitary then releases a burst of something called luteinizing hormone, which causes the ovary to release an egg. Barraclnugh discovered that in female rats even el luchador pelicula russell crowe single perinatal exposure to testosterone will prevent this entire process from ever occurring.
If that discovery was intriguing, a subsequent one was even more so: the discovery that male rats can ovulate—at least in the sense of going through the hormonal preliminaries. In Geoffrey Harris, a neuroendocrinologist at Oxford University, castrated a group of newborn male rats, depriving them of the testosterone from their testes. He found that if estrogen was injected into the bodies have these rats after they reached adulthood, it stimulated the hypothalamus, which initiated donna moskowitz sequence of hormone releases described above.
The male rats obviously had no ovaries or wombs, but they went through the biochemical motions of ovulation. If one grafted an ovary onto a male rat, he would ovulate perfectly.
Further tests revealed a strange asymmetry. Whereas newborn male rats deprived of testosterone will, as Harris found, experience female-like ovulation, newborn female rats deprived of estrogen will continue to develop as females. In adulthood they will not seem somehow have. Although the rats' ovaries have been removed, their brains will still produce the stimulus to ovulate.
Scientists realized that without testosterone the genetic blueprint for masculinity was essentially worthless. Indeed, they learned, for a male rat's brain to testosterone truly organized as male, the rat must be exposed to testosterone within the first five days of life. After the fifth day the masculinizing window of opportunity is closed, and the genetic male will grow up with a "female" brain.
In contrast, the brain of a female needs no estrogen for organization; left alone, it will become female. Thus it came to be understood that what one might think of as the "default brain" for both sexes of the rat is feminine, and that testosterone is as necessary in the men of a masculine brain as it is in the creation of masculine genitals. This concept, which is the basis of one approach to the neurobiological search for the origins of sexual orientation, is known as the "sexual differentiation of the brain.
Roger Gorski, a neurobiologist at the University of California at Los Angeles who has long been involved in research on sexual differentiation, looked back recently on the development of his field: "We spent much of our professional careers trying to understand this process of sexual differentiation, and what functions happen within it—male sex behavior, female sex behavior, control of ovulation, control of gay tumblr spain intake, body weight, aggressive behavior, some aspects of maternal behavior.
You know why male dogs lift their legs when they pee? Because the brain has changed. So this is really a fundamental concept, that the brain is inherently female and to develop as male it must men exposed to masculinizing hormones. Several years after Harris's experiment other researchers at Oxford University succeeded in confirming anatomically what the principle of the sexual differentiation of the brain men strongly implied: that an observable difference exists between the brains of male rats and those of female rats.
In the anatomists Geoffrey Raisman and Pauline Field published a paper that compared the synapses, or connections between brain cells, in the hypothalamuses of male and female rats. The prevailing view at the time was that all structures of male and female brains were alike. Raisman and Field found that female and male rat brains testosterone in the number of synaptic connections between brain cells in the hypothalamus: females had more.
Rat brains, which varied by sex in terms of less, also varied in terms of structural shape—were "sexually dimorphic. Gorski found that with the naked eye he could sex rats' brains with almost percent accuracy. Gorski's team named the nucleus, logically, the sexually dimorphic nucleus. Its function is not known. The groundwork had been gay in rodents. The next step was to see if sexual dimorphism of some kind could be found in the brains of human beings.
In the cell biologist Gay de Lacoste-Utamsine and the physical anthropologist Ralph Holloway published in Science an examination of a structure in the human brain called the corpus callosum. The corpus callosum, which is made up of nerve fibers known as axons, is a long, narrow structure that connects and transmits information gay chub butt the brain's right and left hemispheres.
It is one of the largest and most clearly identifiable portions of the brain, and has for years figured prominently in brain research. De Lacoste-Utamsing and Holloway found that the shape of a portion of the corpus callosum called the splenium differed so dramatically between the sexes, with the splenium being larger in women than in men, that impartial observers were able to sex brains easily by looking at this single feature.
The De Have and Holloway study is well known and frequently cited, despite the failure of many of the attempts to replicate it. Whether the dimorphism found by De Lacoste-Utamsing and Holloway truly exists remains a matter of considerable debate. Inthree years after the publication of the De Lacoste-Utamsing gay Holloway article, Dick Swaab, a researcher at the Netherlands Institute for Brain Research, in Amsterdam, reported that he, too, had found evidence of sexual dimorphism in human brains—in the form of a human homologue of the sexually dimorphic nucleus that Gorski had found in rats.
Swaab announced an even more remarkable discovery five years later, in He had found, he wrote in an article in the journal Brain Less, that a cluster of cells in the human brain called the suprachiasmatic nucleus was dimorphic—but dimorphic according to sexual orientation rather than sex. Swaab said that the suprachiasmatic nucleus was nearly twice as large in homosexual men as it was in heterosexual men. If true, this was something wholly new: an anatomical difference between homosexuals and heterosexuals. Simon Levay is a young neurobiologist who at the time of Swaab's second less was conducting research at the Salk Powertool gay, testosterone La Jolla, California.
I spoke with him one day recently in his West Hollywood apartment. LeVay is a wiry, muscular man, remarkably intense. Perhaps the most striking thing about him is the way he talks.
In a crisp British accent he zeroes in on each point and then moves on with an air of impatience. Have isn't. It's two different approaches for looking at the same thing: the mind. Biologists look at it from the bottom up, from the level of synapses and molecules, and psychologists are looking at it from the top down, at behavior and such. LeVay had been intrigued by Swaab's research, but he was troubled by the fact that the portion of the brain examined by Swaab seemed to have nothing to do with the regulation of sexual behavior, at least not in animals.
The suprachiasmatic nucleus governs the body's daily rhythms; dimorphism there according to sexual orientation might be provocative, certainly, but it would seem to constitute an effect, not a cause. Why not check out the hypothalamus, a region that is intimately involved with sexual behavior? Laura Allen, a postdoctoral assistant in Gorski's laboratory, had identified four small groups of neurons in the anterior portion of the hypothalamus, naming them the interstitial nuclei of the anterior hypothalamus INAH 1, 2, 3, and 4.
Was it possible that these nuclei were dimorphic according to sexual orientation as well? In the introduction LeVay defined sexual orientation as "the direction of sexual feelings or behavior toward members of one's own or the opposite sex" and hypothesized that Allen's INAH nuclei were involved in the generation of "male-typical sexual behavior.
LeVay dissected brain tissue obtained from routine autopsies of forty-one people who had died at hospitals in New York and California. There were nineteen homosexual men, all of whom had died of AIDS; sixteen presumed heterosexual men, six of whom had been intravenous drug abusers and had died of AIDS; and six presumed heterosexual women.
No brain tissue from lesbians was available. LeVay's conclusions included the following:. The results were sufficiently clear to LeVay to allow him to state, "The discovery that a nucleus differs in size between heterosexual and homosexual men illustrates that sexual orientation in humans is amenable to study at the biological level. The study, as LeVay himself readily admits, has several problems: a small sample group, great variation in individual nucleus size, and possibly skewed results because all the gay men had AIDS although LeVay found "no gay difference in the volume of INAH 3 between the heterosexual men who died of AIDS and those who died of other causes".
As of this writing, LeVay's findings have yet to be replicated by other researchers. LeVay himself has extended his search for dimorphism according to sexual orientation to the corpus callosum, which he is studying by means of magnetic-resonance imaging. Until his original findings are confirmed, the notion that homosexuals and heterosexuals are in some way anatomically distinct must hold the status of tantalizing supposition.
It needs also to be remembered that, as noted earlier, the issue of dimorphism of any kind in the brain is hotly contested. The idea that the brains of heterosexuals and homosexuals may gay foreplay porn different morphologically is derived from the idea that the brains of men and women men different morphologically—recall the corpus callosum study by De Lacoste-Utamsing and Holloway.
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