In a investigation in the Philippines they measured the blood testosterone levels of more than 600 young men over nearly five years. They observed, on the one hand, that those with higher levels of the hormone at the beginning of the study were, four and a half years later, more likely to have married and become fathers than men with lower levels.
This result should not surprise anyone. Testosterone has diverse effects on males. At puberty, it is responsible for the development of a good number of secondary sexual characteristics, such as the appearance of facial and body hair, the worsening of the tone of voice, the growth of the Adam’s apple, the production of muscles, the growth of the penis, sperm production, and angular facial configuration.
In adulthood it stimulates the libido, predisposes one to be more aggressive with one’s peers and induces courting the person with whom one wants to pair up. It is, therefore, the hormone that promotes mating and competition with other men.
More interesting turned out to be another of the results of the investigation: that the young people who participated in the study after becoming parents experienced sharp drops in testosterone levels. These declines were significantly greater than those experienced by men who had not been fathers due to age. And as if all this were not enough, the drop in testosterone was greater in parents who paid more attention to their children than in those who hardly took care of them.
Testosterone in mammals and birds
In species in which males assume part of the task of caring for the offspring, or contribute their food supply to their rearing, their reproductive success depends on the amount of effort they put into this task. And because time and other resources are limited, those dedicated to trying to mate with other reproductive pairs cannot be devoted to caring for the progeny, so these two tasks are in conflict.
That is, the more resources devoted to brood care, the less can be devoted to finding additional breeding partners. It therefore seems logical that testosterone, given its role in the physiology and psychology of mating, plays an important role in the regulation of this alternative.
In birds, indeed, testosterone has been shown to fulfill this relevant role. However, until this study in the Philippines, a clear relationship between multiple mate trade-off terms and nurturing had not been established in mammals, although there were several observations that had not been sufficiently considered. conclusive.
Thus, if testosterone remained at high levels after fatherhood, it would increase the probability that the man would spend too much time and energy looking for another possible partner, and this would be detrimental to the attention to his children. And the possible gain in terms of reproductive success that could be derived from having children with the new partner would be offset by the possible loss that would result from diminishing his contribution to the care and attention of those he already has.
Therefore, through its effects on testosterone, fatherhood decreases the probability that men will seek other reproductive partners and dedicate effort and resources to it.
The original version of this article was published in the Scientific Culture Notebook of the UPV/EHU.
Juan Ignacio Perez Iglesias, President of the Advisory Committee of The Conversation Spain. Professor of Physiology, University of the Basque Country / Euskal Herriko Unibertsitatea
This article was originally published on The Conversation. read the original.
