Rhawn Gabriel Joseph, Ph.D.
Human sexual behavior, including gender differences in cognitive and emotional functioning are influenced by a number of hormonal, neurological, as well as environmental variables (Beach, 2004; Beatty, 2002; Grumbach, 2005; Harris, 1978; Harmson, 1990; Money & Ehrhard, 1972). However, as is apparent by the sexual activities of reptiles, amphibians, and fish, the basic rudiments of sexual activity, including sexual orientation, is genetically determined and under the neurological and hormonal control of the limbic system, specifically, the interactions of the amygdala, hypothalamus, and septal nuclei (Joseph, 1990, 2002a, 2003; Maclean, 1990). Early experience, exposure to certain role models, parental attitudes, and so on, are almost wholly irrelevant to non-mammalian species insofar as sexual activity is concerned. Indeed, as is well known, the infants of many of these creatures shun parental contact so as to avoid being cannibalized (Joseph, 2003; Maclean, 1990).
THE LIMBIC SYSTEM: A SEXUAL OVERVIEW
Buried within the depths of the cerebrum are several large aggregates of limbic structures and nuclei which are preeminent in the control and mediation of memory, emotion, learning, dreaming, attention, and arousal, and the perception and expression of emotional, motivational, sexual, and social behavior including the formation of loving attachments.
In general, the primary structures of the limbic system include the hypothalamus, amygdala, hippocampus, septal nuclei, and anterior cingulate gyrus; structures which are directly interconnected by massive axonal pathways (Gloor, 2007; MacLean, 2000; Risvold & Swanson, 2006).
The hypothalamus could be considered the most "primitive" aspect of the limbic system, though in fact the functioning of this sexually dimorphic structure is exceedingly complex. The hypothalamus regulates internal homeostasis including the experience of hunger and thirst, can trigger rudimentary sexual behaviors or generate feelings of extreme rage or pleasure. In conjunction with the pituitary the hypothalamus is a major manufacturer/secretor of hormones and other bodily humors, including those involved in the stress response and feelings of depression.
Indeed, the hypothalamus is highly involved in all aspects of emotional, reproductive, vegetative, endocrine, hormonal, visceral and autonomic functions (Alam et al., 1995; Johnson & Gross, 1993; Markakis & Swanson, 2007; Sherin, et al., 2006; Smith et al. 2000) and mediates or exerts significant or controlling influences on eating, drinking, sleeping and the experience of pleasure, rage, and aversion.
Structurally and functionally the hypothalamus of males and females are stucturally dissimilar (Bleier et al. 1982; Dorner, 1976; Gorski et al. 1978; Rainbow et al. 1982; Raisman & Field, 2006, 1973) and perform different functions depending on if one is a man or a woman, and if a woman is sexually receptive, pregnant, or lactating. For example, the sexually dimorphic supraoptic and paraventricular nuclei project (via the infundibular stalk) to the posterior lobe of the pituitary which may then secrete oxytocin--a chemical which can trigger uterine contractions as well as milk production in lactating females (and which can thus make nursing a pleasurable experience). The male hypothalamus/pituitary does not perform this function.
SEXUAL DIMORPHISM IN THE HYPOTHALAMUS
As is well known, sexual differentiation is strongly influenced by the presence or absence of gonadal steriod hormones during certain critical periods of prenatal development in many species including humans. Not only are the external genitalia and other physical features sexually differentiated but certain regions of the brain have also been found to be sexually dimorphic and differentially senstitive to steriods, particularly the preoptic area and ventromedial nucleus of the hypothalamus, as well as the amygdala (Bleier et al. 1982; Dorner, 1976; Gorski et al. 1978; Rainbow et al. 1982; Raisman & Field, 2006, 1973).
This is a consequence of the presence or absence of testosterone during fetal development in humans, or soon after birth in some species such as rodents. Specifically, the presence or absence of the male hormone, testosterone during this critical neonatal period, directly effects and determines the growth and pattern of interconnections between the amygdala and hypothalamus, between axons and dendrities in these nuclei as well as the hippocampus, septal nuclei, olfactory system, and thus the organization of specific neural circuits.
In the absence of testosterone, the female pattern of neuronal development occurs. Indeed, it is the presence or absence of testosterone during these early critical periods that appear to be responsible for neurological alterations which greatly effect sex differences in thinking, sexual orientation, aggression, and cognitive functioning (Barnett & Meck, 2000; Beatty, 1992; Dawson et al. 1975; Harris, 1978; Joseph, et al. 1978; Stewart et al. 1975).
For example, if the testes are removed prior to differentiation, or if a chemical blocker of testosterone is administered thus preventing this hormone from reaching target cells in the limbic system, not only does the female pattern of neuronal development occur, but males so treated behave and process information in a manner similiar to females (e.g., Joseph et al. 1978); i.e. they develop female brains and think and behave in a manner similar to females. Conversely, if females are administered testosterone during this critical period, the male pattern of differentiation and behavior results (see Gerall et al. 1992 for review).
That the preoptic and other hypothalamic regions are sexually dimorphic is not surprising in that it has long been known that this area is extremely important in controlling the basal output of gonadotrophins in females prior to ovulation and is heavily involved in mediating cyclic changes in hormone levels (e.g. FSH, LH, estrogen, progesterone). Chemical and electrical stimulation of the preoptic and ventromedial hypothalamic nuclei also triggers sexual behavior and even sexual posturing in females and males (Hart et al., 1985; Lisk, 1967, 2006) and, in female primates, even maternal behavior (Numan, 1985). In fact, dendritic spine density of ventromedial hypothalamic neurons varies across the estrus cycle (Frankfurt et al., 2000) and thus presumably during pregnancy and while nursing.
In primates, electrical stimulation of the preoptic area increases sexual behavior in males, and significantly increases the frequency of erections, copulations and ejaculations, we well as pelvic thrusting followed by an explosive discharge of semen even in the absence of a mate (Hart, et al., 1985; Maclean, 1973). Conversely, lesions to the preoptic and posterior hypothalamus eliminates male sexual behavior and results in gonadal atrophy.
Hence, it is thus rather clear than the ability to sexually reproduce is dependent on the functional integrity of the hypothalamus. In fact, it is via the hypothalamus acting on the pituitary, that gonadotropins come to be released. Gonadotropins control the production and/or release of gametes; i.e. ova and sperm.
Specifically, the hypothalamic neurons secrete gonadotropin-releasing hormone, which acts on the anterior lobe of the pituitary which secretes gonadotropins. However, given that in females, this is a cyclic event, whereas in males sperms are constantly reproduced, is further evidence of the sexual dimorphism of the hypothalamus.
THE HOMOSEXUAL HYPOTHALAMUS
Although the etiology of homosexuality remains in question, it has been shown that the ventromedial and anterior nuclei of the hypothalamus of male homosexuals demonstrate the female pattern of development (Levay, 1991; Swaab, 2000). When coupled with the evidence of male vs female and homosexual differences in the anterior commissure which links the temporal lobe and sexually dimorphic amygdala (see below) as well as the similarity between male homosexuals and women in regard to certain cognitive attributes including spatial-perceptual capability (see below), this raises the possibility that male homosexuals are in possession of limbic system that is more "female" than "male" in functional as well as structural orientation.
In contrast to the primitive hypothalamus, the more recently developed amygdala (the "almond") is preeminent in the control and mediation of all higher order emotional and motivational activities. Via it's rich interconnections with various neocortical and subcortical regions, amygdaloid neurons are able to monitor and abstract from the sensory array stimuli that are of motivational significance to the organism (Gaffan 2002; Gloor 1960, 1992, 2007; LeDoux 2002; Morris et al., 2006; Rolls, 1984, 2002 Steklis & Kling, 1985; Kling & Brothers 1992; Ursin & Kaada 1960). This includes the ability to discern and express even subtle social-emotional nuances such as friendliness, fear, love, affection, distrust, anger, etc., and at a more basic level, determine if something might be good to eat. In fact, amygdaloid neurons respond selectively to the flavor of certain preferred foods, as well as to the sight or sound of something that might be especially desirable to eat (Fukuda et al. 2002; Gaffan et al. 1992; O'Keefe & Bouma, 1969; Ono et al. 1980; Ono & Nishijo, 1992) including even the sight of drugs that induce extreme pleasure.
For example, it has been shown, using positron emission tomography, that detoxified cocaine users not only respond to a cocaine video with cocaine craving, but with increased amygdala (and anterior cingulate) activity (Childress, et al., 1999). The amygdala is exceedingly responsive to social and emotional stimuli as conveyed vocally, through touch, and via the face (Gloor, 1992; Halgren, 1992; Kling & Brothers 1992; Morris et al., 2006; Rolls, 1984, 1992).
In fact, the amygdala, as well as the overlying (and partly coextensive) temporal lobe, contains neurons which respond selectively to smiles and to the eyes, and which can differentiate between male and female faces and the emotions they convey (Hasselmo, Rolls, & Baylis, 1989, Heit et al., 1988; Kawashima, et al., 1999; Rolls, 1984).
For example, the left amygdala acts to discriminate the direction of another person's gaze, whereas the right amygdala becomes activated while making eye-to-eye contact (Kawashima, et al., 1999). Moreover, the normal human amygdala typically responds to frightened faces by altering its activity (Morris et al., 2006), whereas injury to the amygdala disrupts the ability to recognize faces (Young, Aggleton, & Hellawell,1995). With bilateral destruction, emotional speech production and the capacity to respond appropriately to social emotionally stimuli is abolished (Lilly, Cummings, Benson, & Frankel, 1983; LeDoux, 2006; Marlowe, Mancall, Thomas,1975; Scott, Young, Calder, Hellawell, Aggleton, & Johnson, 2007; Terzian & Ore, 1955).
SEXUAL DIFFERENTIATION OF THE MEDIAL AMYGDALA
The medial amygdala receives fibers from the olfactory tract, and via a rope of fibers called the stria terminalis projects directly to and receives fibers from the medial hypothalamus (via which it exerts inhibitory influences) as well as the septal nucleus (Amaral et al, 1992; Carlsen et al. 1982; Gloor, 1955; McDonald 1992; Russchen, 1982; Swanson & Cowan, 1979). The stria terminals is significantly larger and thicker in males vs females (Allen & Gorksi 1992) which suggests that information and impulse exchange (or inhibition) between the hypothalamus and amygdala is different in men vs women.
Moreover, in humans, the amygdala in general is large in males than in females, and in primates, the medial amygdala is sexually differentiated (Nishizuka & Arai, 1981; see also Simerly, 2000), such that the male amygdala contains a greater number of synaptic connections and shows different patterns of steroidal activity (Nishizuka & Arai, 1981; Simerly, 2000). In fact, the human amygdala is 16% larger in the male in total volume (Filipek, et al., 1994) whereas in male rats, the medial amygdala is 65% larger than the female amygdala and grows or shrinks in the presence of testosterone (Breedlove & Cooke, 1999).
The female medial amygdala is a principle site for uptake of the female sex hormone, estrogen, and contains a high concentration of leutenizing hormones (Stopa et al., 1991) which are important during pregnancy and nursing. In fact, the female medial amygdala fluctuates immunoreactive activity during estrus cycle, being highest during proestrus (Simerly, 2000). Moreover, the medial amygdala projects directly to the ventromedial hypothalamus and the preoptic area of the hypothalamus which, as noted above, are sexually differentiated (e.g. Allen et al., 1989; Gorski, et al., 1978; Le Vay, 1991; Raisman & Field, 2006), and which when activated produce sex specific behaviors (Hart et al., 1985; Lisk, 1967, 2006; MacLean, 1973) and, in primates, even maternal behavior (Numan, 1985). These amygdala to hypothalamic synapses are excitatory.
Because the medial amygdala is sexually differentiated, and through its massive connections with the hypothalamus and preoptic area, as well as the striatum which controls gross motor and limb movements, when activated, male vs female sexual behavior can be triggered. These amygdala-induced sexual behariors include sexual posturing, penile erection and clitoral tumenence (Kling and Brothers, 1992; MacLean, 2000; Robinson and Mishkin, 1968; Stoffels et al., 1980), thrusing, sexual moaning, ejaculation, as well as ovulation, uterine contractions, lactogenetic responses, and orgasm (Backman and Rossel, 1984; Currier, Little, Suess and Andy, 2006; Freemon and Nevis,1969; Warneke, 1976; Remillard et al., 1983; Shealy and Peel, 1957).
In addition, the medial (and lateral) regions are rich in cells containing enkephalins, and opiate receptors can be found throughout the amygdala (Atweh & Kuhar, 1977; Fallon & Ciofi, 1992; Uhl et al. 1978) and the amygdala becomes exceedingly active when experiencing a craving for pleasure inducing drgus, such as cocaine (Childress et al., 1999). In this regard, the amygdala is capable of inducing extreme feelings of pleasure as well as motivating the individual to engage in pleasure-seeking behaviors such as sexual activity.
The primate amygdala is sexually differentiated (Nishizuka & Arai, 1981; see also Simerly, 2000). As noted, the male amygdala is larger than the female amygdala (Breedlove & Cooke, 1999; Filipek, et al., 1994), contains a greater number of synaptic connections and shows different patterns of steroidal activity (Breedlove & Cooke, 1999; Nishizuka & Arai, 1981; Simerly, 2000). These sex differences are particularly evident in the medial amygdala, which is also a principle site for steroidal uptake, including the female sex hormone, estrogen, and contains a high concentration of leutenizing hormones (Stopa et al., 1991). The number of immunoreactive cells in the female amygdala also fluctuates during the estrus cycle, being highest during proestrus (Simerly, 2000), and thus presumably acts so that if pregant, the fetus will not be attacked as foreign, and/or so as to coordinate, with the hypothalamus, the appropriate neuroendocrine responses during pregnancy and following birth.
In conjunction with the overlying temporal lobe, the male and female amygdala is capable of detecting sexually significant stimuli, and can determine and detect gender differences, which in turn presumably enables the male amygdala to respond to female-visual and olfactury cues and vice versa.
Because the amygdala is involved in sexuality and is sexually differentiated, activation of the amygdala can produce penile erection (Kling and Brothers, 1992; MacLean, 2000; Robinson and Mishkin, 1968; Stoffels et al., 1980) sexual feelings (Bancaud et al., 1970; Remillard et al., 1983), sensations of extreme pleasure (Olds and Forbes, 1981), memories of sexual intercourse (Gloor, 1986), as well as ovulation, uterine contractions, lactogenetic responses, and orgasm (Backman and Rossel, 1984; Currier, Little, Suess and Andy, 2006; Freemon and Nevis,1969; Warneke, 1976; Remillard et al., 1983; Shealy and Peel, 1957).
By contrast, injuries to and/or seizure activity within the amygdala/temporal lobe may result in bizarre sexual changes, such as continuous masturbation and indiscriminate, often hypersexual hetero- and homosexual behaviors including attempts at sex with inanimate objects (Kling and Brothers, 1992; Kluver and Bucy, 1939; Pribram and Bagshaw 1953; Terzian and Ore, 1955). Hypersexuality following amygdala injury has been documented among numerous species, including cats and dogs (Blumer 1970; Kling and Brothers, 1992).
Humans with an abnormally activated or severely injured amygdala/temporal lobe may expose and manipulate their genitals (Leutmezer et al., 1999), masturbate in public, and attempt to have sex with family members or individuals of the same sex (Blumer, 1970; Kolarsky, Freund, Macheck, and Polak, 1967; Terzian and Ore, 1955). Moreover, abnormal activity involving the amygdala and overlying temporal lobe has been associated with the the development of hyposexuality (Taylor, 2006; Heirons and Saunders, 1966; Toon, Edem, Nanjee, and Wheeler, 1989), hypersexuality (Blumer, 1970) as well as homosexuality, transvestism, and thus confusion over sexual orientation (Davies and Morgenstern, 1960; Kolarsky et al., 1967).
In fact, abnormal- or seizure activity within the amygdala or overlying temporal lobe may induce an individual to engage in "sexual intercourse" even in the absence of a partner. For example, Currier and colleagues (2006, p. 260) described a female temporal lobe seizure patient who was "sitting at the kitchen table with her daughter making out a shopping list" when she suffered a seizure. "She appeared dazed, slumped to the floor on her back, lifted her skirt, spread her knees and elevated her pelvis rhythmically. She made appropriate vocalizations for sexual intercourse such as: It feels so good...further, further."
THE AMYGDALA, THE ANTERIOR COMMISSURE, SEXUALITY & EMOTION,
When the amygdala or the bed nuclei for the anterior commissure of both cerebral hemispheres are damaged, hyperactivated, or completely inhibited a striking disturbance in sexual and social behavior is evident (Brown & Schaffer, 1888; Gloor, 1960; Kluver & Bucy, 1939; Terzian & Ore, 1955; Schriner & Kling, 1953). Specifically, humans, non-human primates, and felines who have undergone bilateral amygdalectomies will engage in prolonged, repeated, and inappropriate sexual behavior and masturbation including repeated sexual acts with members of different species (e.g. a cat with a dog, a dog with a turtle, etc.). When activated from seizures, patients may involuntarily behave in a sexual manner and even engage in what appears to be intercourse with an imaginary partner. This abnormality is one aspect of a complex of symptoms sometimes referred to as the Kluver-Bucy syndrome.
As noted, portions of the hypothalamus and amygdala are sexually dimorphic; i.e. there are male and female amygdaloid nuclei (Bubenik & Brown, 1973; Nishizuka & Arai, 1981). In humans the male amygdala is 16% larger (Filipek, et al., 1994), and in male rats the medial amygdala is 65% larger than the female amygdala (Breedlove & Cooke, 1999), and the male amygdala grows or shrinks in the presence of testosterone--findings which may be related to sex differences in sexuality and aggression. Moreover, female amygdala neurons are smaller and more numerous, and densely packed than those of the male (Bubenik & Brown, 1973; Nishizuka & Arai, 1981), and smaller, densely packed neurons fire more easily and frequently than larger ones--which may contribute to the fact that females are more emotional and more easily frightened than males (chapters 7,13,15), as the amygdala is a principle structure involved in evoking feelings of fear (Davis et al., 2007; Gloor, 2007; LeDoux, 2006).
Moreover, despite myths to the contrary, females, regardless of species, are more sexually active than males, on average (see chapter 8)--that is, when they are in estrus-- and the human female is capable of experiencing multiple orgasms of increasing intensity--which may also be a function of sex differences in the amygdala. That is, since female primate amygdala neurons are more numerous and packed more closely together (Bubenik & Brown, 1973; Nishizuka & Arai, 1981), and as smaller, tightly packed neurons demonstrate enhanced electrical excitability, lower response thresholds, and increase susceptibility to kindling and thus hyper-excitation, the amygdala therefore is likely largely responsible for sex differences in emotionality and sexuality.
Electrical stimulation of the medial amygdala results in sex related behavior and activity. In females this includes ovulation, uterine contractions and lactogenetic responses, and in males penile erections (Robinson & Mishkin, 1968; Shealy & Peele, 1957). Moreover, in rats and other animals, kindling induced in the amygdala can trigger estrus and produce prolonged female sexual behavior.
Moreover, the anterior commissure, the band of axonal fibers which interconnects the right and left amygdala/temporal lobe is sexually differentiated. Like the corpus callosum, the anterior commissure is responsible for information transfer as well as inhibition within the limbic system.
Specifically, the female anterior commissure is 18% larger than in the male (Allen & Gorski 1992). It has been argued that the increased capacity of the right and left female amygdala to communicate (via the anterior commissure) coupled with the more numerous and more densely packed neurons within the female amygdala (which in turn would decrease firing thresholds and enhance communication), and the sex diffferences in the hypothalamus, would also predispose females to be more emotionally and socially sensitive, perceptive, and expressive (Joseph 1993).
Hence, these limbic sex differences induces her to be less aggressive and more compassionate and maternal, and affects her sexuality, feelings of dependency and nurturance, and desire to maintain and form attachments in a manner different than males.
In contrast, whereas the right and left female amygdala are provided a communication advantage not shared by males, the "male" amygdala in turn may be more greatly influenced by the (medial) hypothalamus via the stria terminalis which is larger in men than women (Allen & Gorski 1992). As noted, the male medial amygdala is larger than its female counterpart (Breedlove & Cooke, 1999) and changes in size in response to testosterone, which is significant as the medial nuclei (and testosterone) is directly implicated in negative and aggressive behaviors (see above).
Although environmental influences can shape and sculpt behavior and the functional organization of the brain (chapter 28), most sex differences are innate and shared by other species (see chapters 7 & 8); a direct consequence of the presence or absence of testosterone during adulthood and fetal development (see Gerall et al. 1992; Joseph 1993, Joseph et al. 1978) and the sexual differentiation of the limbic system.
FEMALES ARE MORE EMOTIONAL, RELIGIOUS, NURTURING, etc.
To recapitulate, since the limbic system is concerned with emotion, and since the female amygdala appears to be more emotional, more maternal, and more sexual whereas the male limbic system is more greatly influenced by the activating and aggression inducing hormone, testosterone, sex differences in these and other limbic structures may account for why women and females of many species are more nurturant, empathetic, sympathetic, self-sacrificing, and emotionally sensitive and compassionate (Bakan, 1966; Belle, 1982; Blakemore, 2000; Berman, 1983; Eagly & Steffen, 1984; Fresbach, 1982; Graham, 1988; Hoffman, 1977). Human females have a richer inner emotional life and are better able to understand, perceive, express social-emotional nuances as compared to males (Burton & Levy, 1989; Brody, 1985; Buck, 1977, 1984; Buck et al. 1974, 1982; Card et al. 1986; Eisenberg, et al. 1989; Fuchs & Thelan, 1988; Harackiewicz, 1982; Kemper, 1978; Lewis, 1983, Rubin, 1983; Shennum & Bugental, 1982; Soloman & Ali, 1972; Strayer, 1985).
Females are also more willing to express emotional issues and confide and discuss personal problems with others (Gilbert, 1969; Gilligan, 1982; Demos, 1975; Lutz, 1980; Pratt, 1985; Walker, et al. 1987; Parelman, 1980; Lombardo & Levine, 1981), and are much more likely than a male to cry (de Beauvoir 1952; Thomas, 1993), or to freeze, panic, or run away in fear -functions and behaviors directly associated with amygdala activation.
Even female memories are more emotional and more inclined toward social and interpersonal concerns (Pratt, 1985; Walker, et al. 1987; Friedman & Pines, 1991). Hence, women are superior to men in recalling emotional memories (Pratt, 1985; Walker, et al. 1987; Friedman & Pines, 1991) and can recall events that many men swear did not even occur. In this regard, it is noteworthy that dendritic spine density in the female (rat) hippocampus increases and decreases by as much as 30% during each estrus cycle (Woolley, et al., 2000) which in turn may influence memory. This may explain why estrogen replacement therapy slows memory loss in women and results in a 54% lower chance of developing Alzheimers (see chapter 16).
In contrast, males have difficulty discussing personal difficulties or expressing their emotions other than anger and happiness (Balswick, 1982, 1988; Campbell, 2000; Goldberg, 1976; O'Neil, 1982; Joseph, 1992b, 1993; Sattel, 1989) and are much more inclined to develop psychopathological conditions such as sociopathy (Draper & Harpending, 1988). Many male criminals are sociopaths and sociopaths in general have very little human regard, empathy, compassion, or concern for others.
As will be discussed in further detail in chapter 9, activation of the amygdala-temporal lobes are also associated with the capacity to have religious experiences. Sex differences in this structure may explain why women are not just more emotional, but have more intense religious experiences, attend church more often, are more involved in religious activities, involve their children more in religious studies, hold more orthodox religious views, incorporate religious beliefs more often in their daily lives and activities, and pray more often as well (Argyle & Beit-Hallahami, 1975; Batason & Ventis, 1982; De Vaus & McAllister Glock et al. 1967' Lazerwitz, 1961; Lindsey, 2000' Sapiro, 2000). Presumably this sex difference too is a consequence of sex differences in the structure and function of the limbic system, the amygdala and anterior commissure in particular.
THE LIMBIC SYSTEM & TESTOSTERONE
In large part these and related sex differences in aggressiveness are also a consequence of the relatively higher concentrations of the activating hormone, testosterone flowing through male bodies and brains. The overarching influence of neurological and hormonal predispositions are also indicated by studies which have shown that females who have been prenatally exposed to high levels of masculinizing hormones (i.e. androgens) behave similar to males even in regard to spatial abilities (Joseph et al. 1978; see Gerall et al. 1992). They are also more aggressive and engage in more rough and tumble play as compared to normal females (Money & Ehrhardt, 1972; Ehrhardt & Baker, 1974; Reinisch, 1974) and this is also true of other species such as dogs, wolves, gorillas, baboons, and chimpanzees.
Similarly, female primates and mammals who have been exposed to testosterone during neonatal development display an altered sexual orientation, as well as significantly higher levels of activity, competitiveness, combativeness and belligerence (Mitchell, 1979). Nevertheless, it is important to re-emphasize that it is generally the presence or absence of testosterone during the critical period of neuronal differentiation which determines if one is in possession of a "male" vs "female" limbic system.
SEXUAL ORIENTATION & HETEROSEXUAL DESIRE
As noted, the amygdala surveys the environment searching out stimuli, events, or individuals which are emotionally, sexually or motivationally significant. Moreover, it contains facial recognition neurons which are sensitive to different facial expressions and which are capable of determining the sex of the individual being viewed and which become excited when looking at a male vs female face (Leonard et al. 1985; Rolls 1984). In this regard, the amygdala can act to discern and detect potential sexual partners and then motivate sex-appropriate behavior culminating in sexual intercourse and orgasm.
That is, an individual who possess a "male" limbic system is likely to view the female face, body and genitalia as sexually arousing because the amygdala and limbic system responds with pleasure when stimulated by these particular features. Conversely, male physical features are likely to excite and sexually stimulate the limbic systems possessed by heterosexual females and homosexual males (Joseph, 1993). This is because, at a very basic level emotional, sexual, and motivational perceptual/behavioral functioning becomes influenced and guided by the anatomical sexual bias of the host.
Homosexuality, and "homo-phobia" are not uncommon among males of many different species. Often, however, what appears to be "homosexuality" is in fact a dominance display, with the dominant animal mounting the submissive. In some instances, such as involving multi-male/female primates societies, subordinate males and females will present their derriere to a superior, for mounting, in which case the dominant may simulate sexual intercourse. In some instances, however, an animal will attempt to mount another, so as to establish dominance, and in consequence is violently assaulted, and may be mounted in turn.
Among humans this violent reaction to homosexuality is sometimes referred to as "homophobia." That is, a heterosexual male may respond with a violent attack in reaction to a homosexual overture, so as to establish that it is HE who is dominant--and in some cases, this "homophobic" male may then force the "victim" to perform fellatio, or the victim's genitals may be attacked.
VIOLENCE & HOMOSEXUALITY
Homosexuals Sometimes Display Violent Homophobia
As I have noted elsewhere (Joseph, 1992b), in some instances of "homophobic" violence, the attacker is in fact beating upon his own unknown face. Homosexuals are often beat up and attacked by other homosexuals--including those males who do not know, but who fear that they, themselves may be "queer." These latter males may in fact go out in search of a "queer" to beat up, and may force the "queer" to perform fellatio.
A great deal of "gay" violence, is in fact perpetrated by homosexuals, including those who know they are homosexual, and who are in homosexual relationships.
As an illustrative example, a San Francisco homosexual organization, "Community United Against Violence" and which tracks "anti-gay violence" has repeatedly reported, beginning in 1995 when they first began tracking these behaviors, that same-sex domestic violence exceeded "anti-gay violence." Same-sex domestic violence, as this and other homosexual organizations admit, is significantly underreported. Moreover, whereas homosexual domestic violence actually involves violent physical assaults and frequent battering (Lobel, 1988), the above and other homosexual groups, such as the National Coalition of Anti-Violence Programs, considers "slurs" or "yelling out a car window" to be a form of "anti-gay" violence. Hence, actual physical violence against homosexuals is predominantly committed by homosexuals.
Indeed, in a recent series of articles printed in the exceedingly pro-homosexual newspaper, the San Francisco Chronicle (e.g see Heredia, 9/23/2000, page A25), it was reported that the radical homosexual group, ACT-UP/San Francisco, has been engaging in "a campaign of intimidation and violence" against homosexuals including "felony assault" on public health officials. "Members of the group face trial for assault on several employees of the AIDS group Project Inform" and according to witnesses, have been "formenting terror" in the homosexual community.
In a recent PBS series on those who murder homosexuals, it was also inadvertently revealed that almost every single individual convicted of murdering a homosexual had previously had sex with men. And in some cases, groups of men who have had sex together went out as a group in search of homosexuals they could rob, beat and murder. One can only wonder if they are seeking to destroy what they hate most about themselves: their secret, unknown face.