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Carole Jahme shines the cold light of evolutionary psychology on readers' problems. This week: Love, sex and masturbation

From an anonymous male, aged 40+
I had a few very loving, love, "serious" relations, as adults, nor frivolous, and no one (at least on a conscious level - who knows what the hell 's happening to me subconsiously ) to time the short term.

Inevitably, however, my sexual attraction for my partner wanes to the point where we become virtually non-sexual. This can happen in less that a year after the relationship started. This condition consistently contributes to the relationship falling apart. My emotional feeling of love stays constant, and the breakup is traumatic for both of us. Add to the mix my undeniable enjoyment of and never-failing satisfaction with masturbation, and it seems to be a recipe for disaster. Is there an evolutionary take on any of this?

Carole replies:
An attempt to preserve long-term relationships that are presented as sexual people with chemical catch-22.

Studies on the length of relationships have shown that couples in harmonious, stable and trusting long-term relationships have higher blood levels of oxytocin (a chemical that regulates attachment, promotes cooperation and facilitates sensations of joy and love) than people who are not in compatible relationships.¹These happy couples will also receive other benefits in terms of life expectancy, lower rates of alcoholism, depression and illness, and more rapid recovery after accidental injury. ^2,3,4

But there are conflicting chemicals at work in sexual relations, which sometimes prevents them from ever becoming in the long term. Dopamin is a neurotransmitter in the limbic system â€" the brain's primitive reward centre. It mediates both the sex drive and addiction to drugs. Brain scans have shown that the rapid rise in dopamine levels during orgasm is similar to that seen in a heroin high.⁵ But dopamine falls rapidly following orgasm in both males and females and is replaced with rising levels of a hormone called prolactin.

Both parts of the brain 'S "dopamine" reward system.

At first, rising prolactin causes sleepy post-orgasm contentment. (Interestingly the amount of prolactin produced is far greater after sex with a partner than after masturbation. Thus there is little prolactin relief for those who masturbate.) But once this sleepy feeling of satiation has passed, prolactin may go on rising and cause problems for couples wanting to sustain a long-term sexual relationship. In both men and women excess levels of prolactin can cause loss of libido, anxiety, headaches, mood swings and depression.⁶

High prolactin is associated with sensations of despair. When the prolactin levels of newly caged wild monkeys were monitored, the hormone was seen to rise once the animals realised they were trapped.⁷ Levels of the hormone were much higher in monkeys incarcerated for months compared with wild animals that had only just been caged. Science has yet to determine how long prolactin continues to rise and remain high in humans after orgasm, so this is speculative, but in a relationship with lots of sex it could mean levels are elevated for weeks or even months.

How does all this tie in with your predilection for maturbation? There have been some illuminating studies of this behaviour in non-human primates. It has been found, for example, that male monkeys who masturbate tend to be of low status, whereas high-status male monkeys are likely only to experience ejaculation during sex.⁸ It also seems that the frequency of masturbation is higher in captive primates than in wild animals. You can make of this what you will.

Dopaminergic system varies from person to person, some people exhibit greater the reward seeking behavior than others, and this may somehow explain why many relationships burned a year. ⁹ In reproductive terms, 12 months is long enough for fertilisation to take place. It is also certainly long enough for prolactin levels to rise. Once your libido flags and anxiety sets in, the short-term reward gained from masturbating may give you a dopamine "high" without risking bringing on that post-orgasmic prolactin "low".

Chemical compatibility is essential to all good relationships. Couples lucky enough to enjoy long-term partnerships may have similar sex drives (perhaps not too much sex, or even none at all?) and dopaminergic systems that don't flood their bodies with too much prolactin. Human behaviour seems to be under the control of two evolutionary programs: one that results in fertilisation, disillusionment and a series of partners, and the other that enables humans to develop the lasting relationships that lead to long, happy and healthy lives.

References
1. Carter, SC (1998) Neuroendocrine perspectives on social attachment and love. Psychoneuroendocrinology; 23(8): 779-818.
2. DeVries, C, Glasper, ER (2005) Social structure influences effects of pair-housing on wound healing. Brain, Behavior, and Immunity; 19(1): 61-68.
3. Coan, JA et al (2006) Lending a hand: social regulation of the neural response to threat. Psychological Science, A Journal of the Association for Psychological Science; 17(12): 1032-1039.
4. Holden, AEC et al (2008) The influence of depression on sexual risk reduction and STD infection in a controlled, randomized intervention trial. Journal of Sexually Transmitted Diseases; 35(10): 898-904.
5. Holstege, G et al (2003) Brain activation during human male ejaculation. Journal Neuroscience; 23 (27): 9185-9193.
6. Heaton, JPW (2003) Prolactin: An integral player in hormonal politics. Contemporary Urology, 15: 17-25.
7. Suleman, BVM, Mbaruk, A et al. (2004) Physiologic manifestations of stress from capture and restraint of free-ranging male African green monkeys (Cercopithecus aethiops). Journal of Zoo and Wildlife Medicine; 35(1): 20-24.
8. Thomsen, R, Soltis, J (2004), male masturbation in a free range of Japanese macaques. International Journal of Primatology; 25(5): 0164-0291.
9. Guo, G, Tong, Y et al (2007) Dopamine transporter, gender and number of sexual partners among young people. European Journal of Human Genetics; 15: 279â€"287.

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