2. Sex in Our Genitals

In order to obtain semen samples from animals, electroejaculation is used. An electrical charge is administered inside the anus, near the prostate, activating the PC (pubococcygeus) muscle, thus bringing about ejaculation as a reflexive act.

Scientists still are not entirely clear on all the neurophysiological factors implicated in mental stimulation. They do know that, with sensory stimulation or fantasies, the hypothalamus can secrete oxytocin and send a signal through the spinal cord that activates the pelvic nerve and the hypogastric nerve, and that they can cause an immediate erection in a mouse by electrically stimulating a particular part of its brain. But, as we will see later in this book, our bodies have reactions that leave even the most experienced physiologists stumped.

The opposite occurs with nocturnal erections. They usually take place during the REM phase, and coincide with a decrease in activity in a specific area of the brainstem that radically deactivates the sympathetic system, generating a very favorable balance toward the parasympathetic, leading to an erection.

In fact, the relationship between the sympathetic system and orgasm is so clear that if you are having sex with a woman and she moans and squirms, but her pupils don’t dilate, her heart rate doesn’t shoot up and the sudden increase in blood pressure doesn’t break a few capillaries leaving her cheeks and the upper part of her chest red, you should probably be suspicious.

There are also natural products and dietary supplements that work very well for erectile problems. Interestingly, according to a study realized by Pfizer, in many of those products sold as alternatives the manufacturers have added small doses of the active ingredient in Viagra. It is also interesting to note that sildenafil was a pharmaceutical that was being studied to counteract arterial hypertension, and when they began the clinical studies with patients, the scientists noticed a curious side effect: it provoked erections. They changed the target of their studies and it became a multimillion-dollar business for Pfizer.

Evolutionary psychologists love to propose hypotheses consistent with natural selection that, later, are rarely put to test experimentally. One that was very popular for interpreting the logic of the female orgasm was the up-suck theory, according to which the muscular contractions during orgasm would carry the semen to the cervix and increase the possibility of pregnancy. While at first the up-suck theory was widely circulated because it was logical and generated the typical “oh, of course” response, later experiments refuted it. Having an orgasm doesn’t significantly improve the possibilities of fertilization, and many evolutionists still think that the female orgasm has no evolutionary function, that it simply exists because the physiology of female genitals is the same as male ones.

Founded in 1947 by researcher Alfred Kinsey (whom we will discuss in detail in Chap. 4), the Kinsey Institute at Indiana University is perhaps the most emblematic research center worldwide devoted exclusively to the study of human sexuality from a multidisciplinary standpoint. Currently headed by Julia Heiman, its staff contains biologists, psychologists, anthropologists, sociologists, historians and experts in sexual behavior. Its library has one of the largest collections in the world of printed and audiovisual material about sex, and it is a point of reference for any and every sex researcher.