The hormonal profile: Priming for sexual desire
We now look at the changing hormonal profile which plays a role both in the priming of sexual interest and in the activation of sexual arousal. Determining the hormonal contribution during various periods of development and determining the effect of various contexts on the hormonal profile is difficult, both in the measurement of hormonal fluctuation and in the isolation of variables — not only in relation to what might result from hormonal change, but also in relation to what might contribute to it. Nevertheless, it is clear that hormones influence sexual desire in the most general sense, and that various neurochemicals are activated both in the process of sexual arousal and in the subsequent sexual encounter. In a woman, for example, the rhythm of sexual desire is intimately connected with the biology of her reproductive systems as expressed in her hormonal profile, both in her monthly cycles, and in the seasons of her lifetime.
As is true of other aspects of the mind-body relationship, biochemical and psychological processes interact. And so, for example, subjective mood states can affect the hormonal profile affecting sexual desire, while subjective experiences (for example, sexual thoughts or fantasies) can translate into neuro-chemical activation that creates subsequent conditioned arousal responses to those particular thoughts and fantasies. Furthermore, a person’s hormonal profile is in a constant state of flux,96 responding to physiological events (the internal biological context, such as the menstrual cycle and pregnancy in women97), to external circumstances (the prevailing environmental context, such as relationship circumstances), and to developmental and life-cycle changes. The prevailing hormonal profile at critical developmental periods can also have enduring effects, especially when it contributes to subjective associations and conditioning processes. That is, hormones can activate or inhibit certain sexual behaviours at one time, which creates implicit memories affecting later sexual behaviour.
On the basis of such research as has been done in this area, we have glimpses into the complexities of the interaction of the hormonal profile and these various factors. But we begin with the reminder that although both men and women carry the hormones testosterone and oestrogen, their profiles are different. Testosterone, a hormone of the androgen group, has been associated not only with the development of male physical sexual characteristics, but also with the regulation of cognitive and physical energy. Testosterone associates with sexual motivation in men, although it does not affect the ability to engage in sexual activity.98 In women, the release of oestrogen relates to sexual motivation, while release of progesterone has the reverse relationship.99
But the effect of the hormonal profile on sexual behaviour begins long before men and women develop sexual interest. It begins before birth, as a mother’s hormonal activity affects the baby within her. The sperm fertilising the egg determines whether the baby will be male or female. However, the baby’s physical masculine or feminine characteristics is shaped by the mother’s prevailing hormonal profile during the first trimester of her pregnancy. The correct concentration of testosterone at the right time is prerequisite to the physical development of male features; otherwise, female features develop. This in turn sets the biological framework for later patterns of sexual attraction and desire as the baby grows and eventually enters adulthood.
During the second trimester, evidence suggests that the mother’s androgen levels shape aspects of the baby’s brain, influencing gender formation. Testosterone (converted to oestradiol) contributes to masculinisation in interest and behaviour. Too much testosterone can have a masculinising effect on a developing girl, so that she later comes to prefer ‘male’ toys, activities, and playmates, has decreased interest in feminine behaviours such as playing with dolls, is more socially detached, engages in less verbal aggression (but more physical aggression) and is later less likely to have exclusively heterosexual orientation.100 In corresponding manner, a deficit of androgen hormones prenatally may lead to a ‘predominantly female differentiated brain’ which in a boy has been associated with later homosexual tendencies.101
The idea that sexual orientation may be influenced by brain development under the influence of hormonal secretions during critical periods of prenatal development has also found other support.102 For example, a higher incidence of lesbian orientation has been found among women exposed prenatally to a synthetic hormone used to reduce miscarriage (in their mothers) as well as among women with an adrenal disorder resulting in abnormally high androgen levels during prenatal development.103 However, while there is evidence that sexual orientation is affected by prenatal masculinisation or feminisation processes, there is no evidence of the biological inevitability of sexual object choice.104 Moreover, the subsequent prevailing hormonal profile in an adult does not appear to determine the choice of erotic desire: when the hormone levels of homosexuals and heterosexuals were compared, no consistent links with sexual orientation were found.105
The hormonal profile changes over the life cycle, and does so differently for men than for women. Sexual interest, desire, and arousal often begin before puberty, around age ten, for both boys and girls with the maturation of adrenal glands (adrenarche).106 Hormone levels begin to change (with sexual interest and hormonal changes influencing each other), the subsequent onset of puberty being managed by hypothalamic sexual control centres.107 Testosterone levels surge for pubescent boys while pubescent girls experience increasing levels in both testosterone and oestrogen.108 This results in maturation in primary and secondary sexual characteristics, in increased risk-taking and increased sexual interest and activity in boys, and in depression and identity concerns in girls. Unlike its associations with sexual ideation and motivation in boys, testosterone elevation does not relate strongly to sexual activity in girls.109 Generally, as testosterone levels begin their steep incline, any potential issues with sexual identity or orientation emerge.110 Nevertheless, the object of sexual interest appears fluid, especially to begin with. It is not defined by the prevailing hormonal profile: for some boys and for reasons other than hormonal activity, the object of their emerging sexual interest may be other males. These hormonal changes also coincide with changes in relationships with parents, preparing the way for a new attachment with a lover. Perhaps testosterone increase plays a role in motivating the leaving one for the other, along with the establishment of new interpersonal territory. Testosterone levels peak during the 20s, followed by a gradual decline.
Although hormonal levels begin their gradual decline in the 20s, fluctuations continue to occur, affected by both physiological and environmental factors. Testosterone and oestrogen levels fluctuate daily, peaking early in the morning before waking; while seasonal variations also occur, with testosterone levels increasing in autumn in both men and women. Another source of fluctuation is the menstrual cycle in women. Sexual motivation varies systematically during this time. During the peri-ovulatory period of the menstrual cycle, the hormonal profile is characterised by high oestrogen levels and low progesterone levels, with accompanying increase in sexual motivation and likelihood of sexual fantasies,111 and in greater sexual interest in men — including men other than their current partner.112 Lesbian women (and to a lesser extent, bisexual women) report a similar increase in sexual interest (in women) during the oestrogen peak of their cycle, although interest in the opposite sex reportedly decreases.113 The perinatal period in a woman sees dramatic changes in her hormonal profile, lowering sexual interest and enjoyment. With advancing age, testosterone levels continue to drop in men while oestrogen and androgen drops during menopause in women. These changes see a decline in sexual desire and motivation.114
Relationship circumstances also affect hormonal profiles, although results vary. Again, testosterone has received most research attention. It seems testosterone levels are higher in more sexually active men,115 for single men with past relationship experience,116 and in men who have sex with more than one person or with an unfamiliar person.117 Continued high testosterone levels seem to associate with instability in a sexual relationship: there is an association between men with high testosterone levels and the likelihood of extramarital sex, or divorce.118 Some research shows that falling in love decreases men’s testosterone levels (simultaneously increasing