We are all concerned about the proper functioning of our body. However, we do not experience all physical deficiencies and pathologies in the same way.
The number one priority is that we are alive, so, logically, organs such as the brain, lungs and heart enjoy our preferential interest. In relation to the rest, and although they are not absolutely vital, whether the biological gears that intervene in our sexual physiology function properly raises many concerns. In the specific case of the male sex, failure to achieve a correct erection can be experienced as a real drama.
But what happens in other animals? Do they also have erection problems?
What is, physiologically, an erection?
Under normal conditions, an environment conducive to sexual practice activates the autonomic nervous system, which causes increased nitric oxide levels (a vasodilator) in the trabecular arteries and in the smooth muscles of the penis. The consequence is the influx of blood to the penile cavernous bodies and, to a lesser extent, to the corpus spongiosum. Simultaneously, the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa, restricting the outflow and circulation of this blood out of the copulatory appendix.
As a consequence of the opening of the blood entry gate and the closing of the exit gates, the cavernous bodies fill with fluid and swell due to a progressive increase in blood pressure (which can reach several hundred mm Hg) and the penis becomes erect. When parasympathetic activity decreases and the muscles relax, blood is drained by the aforementioned veins and the penis returns to the flaccid state.
It is evident, therefore, that time and stimulation are necessary for the penis to become erect. Nevertheless, facing certain health problems, both physical (mainly cardiovascular) and psychologicalthis system stops working correctly, making copulation impossible and annoying the user.
Are there alternative mechanisms in nature?
Although it may seem surprising, the human penile modality is quite exceptional. In fact, most mammals have “bone assistance” to keep the penis erect. This is the so-called baculum, a bone located on the longitudinal axis of the penis that allows the male to efficiently penetrate at any time but, above all, favors the lengthening of copulation time.
This surprising offspring is very varied. In fact, “the most diverse of all bones” (as it has come to be called) not only acquires plural forms but also manifests very different sizes: from being almost vestigial in some species of lemurs to acquiring surprising dimensions, such as the 65 cm in length that it can reach in males. of walruses.
On the contrary, marsupials, hyenas, some lagomorphs such as rabbits, and also equids share this absence with humans. This group of “discriminated males” also lacks a second advantage, since the staff, when elongated, protects the urethra in prolonged copulations by limiting its distal constriction, keeping it open and facilitating the flow of sperm through it.
But why do men lack penile bone?
If the first primates, emerging at the end of the Cretaceous, had a baculum, and this has been maintained in most of the groups of mammals that have emerged, why was it lost in the evolutionary line that generated our species?
The explanation could be that the staff would favor reproductive strategies in populations with high levels of postcopulatory sexual selection. In fact, polygamous primate species (where sexual competition is very intense) have longer baculums than those of monogamous ones, which would allow them to prolong intercourse. In other words, the female would be kept “busy” for longer, preventing her from copulating with other males and, consequently, increasing the chances that the lucky “baculado” would bequeath his genes to the next generation. This hypothesis has been verified in a curious experiment with two groups of miceone of them forced into monogamy.
And… prize! Over 27 generations, the size of the penile bone was reduced in the monogamous group. It seems, therefore, that if we become monogamous the selection pressure in favor of maintaining the baculum is reduced.
Besides, About two million years ago, the piece of chromosome that contained the DNA sequence coding for the baculum was lost.. This mutation (deletion) occurred when our line of bipedal primates (the hominins) was already well advanced and separated, 4 million years before, from the one that gave rise to chimpanzees and bonobos (which are polygamous and have a baculum).
This would lead us to the interesting conclusion that hominins became monogamous in that time period, making the evolutionary pressures in favor of maintaining the baculum disappear.
Who really loses in this story, the men or the women?
In Unfair Sexrecently published, I explain that things are not always what they seem when viewed through the evolutionary prism.
In the case of the penile bone, apparently, it seems like a clear disadvantage to have to “work” on the erection of the penis, especially when any setback, physical or psychological, can generate more than one compromising situation for men. However, and analyzing this fact from an evolutionary point of view, things would not be so clear. With the disappearance of high levels of postcopulatory sexual competition, the only objective of hominin males during copulation would be restricted exclusively to ejaculation.
If, in terms of biological efficiency, it doesn’t matter if the intercourse is “quick”… couldn’t we think that the ones who really lose are the women?
This article was originally published in The Conversation. You can read it here.
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