June 12, 2020 13h37
Human Nature : the legacy (sexual) evolution
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.
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. […]