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June 12, 2020 13h37
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Human Nature : the legacy (sexual) evolution
Cyrille Barrette
Professor emeritus, biology, University of Laval
THE SCIENCE IN HIS WORDS / the following is a non-exhaustive list of twenty attributes, psychosocial, sexual, or reproductive, very widespread among us and is almost, or even completely absent even among our cousins, the closest […] : eroticism, pornography, prostitution, pedophilia, chastity, celibacy (voluntary or not, religious or secular), adoption, contraception, abstinence, abortion, assisted reproduction, exclusively homosexual (and all the universe LGBTQ++), the c-section.
And, without claiming to be able to confirm what is happening in the minds of other mammals, and, I would add : desire, fantasy, jealousy, modesty, indecency, obscenity, exhibitionism, etc
These characters psychosocial have been forged through cultural capacities of the human, sustained by our sexual nature, organic, result of our long evolution. The few examples of anatomical or physiological changes that follow are a sample of the legacy that bequeathed us our evolution by natural selection. In fact, throughout the nearly six million years that separate the human lineage from that of chimpanzees, more characters breeding that set us apart from other mammals appeared.
The breasts
Like all mammals, we are in possession of mammary glands producing milk, but we are the only species to have breasts. These attributes develop at puberty, and their volume is maintained or even increases, even without pregnancy, or breast-feeding. In addition, during breastfeeding, the quantity of milk produced seem to have little relation with the volume of the breasts. In fact, the glands secreting milk only occupy part of the volume of the breast, the rest being composed mainly of fats.
What can be the function of the breasts ? Since they cost energy and resources to build, maintain and transport, and that milk production is not sufficient to explain their existence, we are tempted to assign them to a social function. It is hard to imagine that they provide no benefit and do not imply that costs ; this would be contrary to the economy of nature, as dictated by natural selection, which requires that the benefits outweigh the costs.
A plausible hypothesis would be that the breasts are a form of characteristic sexual secondary, that is to say, a character linked to procreation, but that is not used directly to make children, as it is the case of sexual characteristics, primary (gonads, uterus and genital organs). It is more of speculation than a scientific hypothesis capable of generating predictions for the test ; but such speculations are useful, they constitute the first step toward the formulation of a scientific hypothesis unconvincing. It can be assumed that the breasts could be the signal announcing the good health and the possession of body reserves sufficient to raise children. […]
Library The Sun
The absence of a baculum
[…] A general rule, one does not describe a species, listing the characters which it does not possess. Such a list would potentially be endless and inane, because the species has not only informs us nothing about what it holds, nor on its behavior.
Tell the elephant that he does not steal does not tell us if it runs, it digs, if it creeps, it climbs, it swims, if it is a biped, if it rolls, etc., This is like stating that an animal is invertebrate. This includes animals as disparate as an oyster, and a butterfly for no other reason than their lack of vertebrae. On the other hand, the comparison of a species with other similar or related may point to the absences surprising and very significant that the explanation provides information on the nature and on the mode of life of the animal. This is the case, for example, a bird that does not fly, of a mammal without teeth, a salamander without lungs, a lizard without legs. The unique aspect of the absence of a characteristic gives it a meaning and requires an explanation, such as silencers (which can be rich in meaning) in a conversation or in music.
A vast majority of mammals have a bone in the penis, the baculum or os priapi. This is the case of rodents (which, in and of themselves, constitute half of the living species of mammals), bats, insectivores, carnivores, and primates. This bone is absent, particularly among cetaceans (whales and dolphins) and ungulates (zebras, giraffes, rhinos, deer, antelopes, elephants). The baculum occupies almost the entire length of the penis of certain species. […]
The authors do not agree on the function of this bone. It certainly plays a role during copulation, but which one ? Is it to ensure a copulation vigorous, prolonged or on demand, to stimulate ovulation, or all of these responses, and others, depending on the species ? It is certainly not indispensable, since several species do not have it and pass over it perfectly ; in addition, its function may not be the same for all species. This structure is frankly curious, and its use is not without risk since it reports some cases of fracture, for example in the wolf and the walrus.
So, how is it that this bone exists in most mammals, including primates, but that man is free ? Again, we fall into pure speculation ; here’s my favorite. We know that the erection of the penis is a matter of blood circulation, and motivation or inspiration.
The result of a dilation of arteries and constriction of veins of the penis, the blood accumulates, which increases the length, size and stiffness, a sort of skeleton hydraulic. These adjustments vascular are under the control of the autonomic nervous system, which itself is activated following the excitement caused by the presence and reproductive status of a female, collected by the male.
In addition, in almost all mammals, the penis at rest is invisible, removed to the shelter of the wall body of the male ; it is not stated that during an erection. However, curiously, in primates, the penis, even at rest, is pendulum, clearly visible at all times. […]
All of these elements suggests that the absence of a baculum human would allow the erection to be the signal honest of the good health of the male, health vascular and social. In fact, a male would be difficult to produce and maintain a full erection if he was suffering from vascular problems or if his social position, lower him to show off his erection for fear of reprisals aggressive of a dominant. However, it is precisely the absence of a baculum human that would give value to this signal in good physical and social health.
With a baculum, a male would seem in erection in all circumstances, as without him, it could not claim to be.
The erection human is therefore a demonstration of truth. As the female is able to observe both states of the penis, it can easily detect the “disabled”, which would be impossible if all the males had a permanent erection thanks to a baculum. This situation is observed only in humans among the primates, may be because there is a greater mental capacity is required to make the connection of cause and effect between the erection of the temporary and the state of health and, the daring, social in the male. […]
The challenge is once again to move from speculation to a hypothesis refutable by observations. The comparative approach would be, once again, useful. So why the spotted hyena is also devoid of baculum, the only exception among the carnivores ? And why among primates, the human is the one whose penis is longest ? The scientific challenge is launched.
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This text is an excerpt from the book “The true nature of the human animal” biologist Cyrille Barrette, published this spring in MultiMondes. Reproduced with permission.
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