I’m coming late to this discussion about how masturbation proves humanity is special, but it did get me blogging again. All titillation aside – and where’s the pseudo-scientific banter about breasts, asses, and other parts of the male and female body – Bering illustrates how messy human evolution really has been..

Bering argues that masturbation – for men it seems for the most part in this discussion – counter-intuitively provides young men with more bang for each pop..

In a now-classic, pre-Internet-porn (I’ll get to that later on) study by British evolutionary biologists Robin Baker and Mark Bellis, male university students were found to masturbate to ejaculation about every 72 hours, and “on the majority of occasions, their last masturbation is within 48 hours of their next in-pair copulation.” If they’re not having intercourse every day, that is to say, men tend to pleasure themselves to completion no more than two days prior to having actual sex.

Baker and Bellis’s quite logical argument for this seemingly counter-intuitive state of affairs (after all, shouldn’t men try to stock up as much sperm as possible in their testes rather than spill their seeds so wastefully in a rather infertile swath of toilet paper or a dirty sock?) is that because there is a “shelf-life” for sperm cells – they remain viable for only 5-7 days after production – and because adult human males manufacture a whopping 3 million sperm per day, masturbation is an evolved strategy for shedding old sperm while making room for new, fitter sperm. It’s quality over quantity. Here are the adaptive logistics.

The advantage to the male could be that the younger sperm are more acceptable to the female and/or are better able to reach a secure position in the female tract. Moreover, once retained in the female tract, younger sperm could be more fertile in the absence of sperm competition [sexually monogamous relationships] and/or more competitive in the presence of sperm competition [in which the woman is having sex with other men]. Finally, if younger sperm live longer in the female tract, any enhanced fertility and competitiveness would also last longer.

Unconvinced? Well, Baker and Bellis are clever empiricists. They also apparently have stomachs of steel. One way that they tested their hypotheses was to ask over 30 brave heterosexual couples to provide them with some rather concrete samples of their sex lives: the vaginal “flowbacks” from their post-coital couplings, in which some portion of the male’s ejaculate is spontaneously rejected by the woman’s body.

The flowback emerges 5-120 min after copulation as a relatively discrete event over a period of 1-2 min in the form of three to eight white globules. With practice, females can recognize the sensation of the beginning of flowback and can collect the material by squatting over a 250 ml glass beaker. [And here comes a useful tip, ladies…] Once the flowback is nearly ready to emerge, it can be hastened by, for example, coughing.

As the authors predicted, the number of sperm in the girlfriends’ flowbacks increased significantly the longer it had been since the boyfriend’s last masturbation — even after the researchers controlled for the relative volume of seminal fluid emission as a function of time since last ejaculation (the longer it had been, the more ejaculate was present). If only the parents of teenage boys had these findings available for the first hundred thousand years of our history, think of all the anxiety, guilt and shame that might never have been.

All those jokes about hairy palms are meaningless, too, because other primates do not masturbate. “The answer for this cross-species difference, I’m convinced, lies in our uniquely evolved mental representational abilities—we alone have the power to conjure up at will erotic, orgasm-inducing scenes in our theater-like heads … internal, salacious fantasies completely disconnected from our immediate external realities.”

There’s also Bering’s faint grasp of female orgasm, as well as what seems these redundant sperm-saving and fantasy proclivities. Human sexuality just appears jerry-rigged. Add in Bering’s contribution to a history of the penis, and I think I need to ask my wife for some research time on this subject.

Filed under: bhtv, Biology, Science Tagged: human sexuality, jesse bering, john horgan, masturbation, penis