The sexy son hypothesis: explaining sexual selection

This explanation of sexual selection focuses on the beauty of male offspring.

What leads a female to select one male out of many? Ever since Richard Dawkins spoke of the selfish gene, several evolutionary scientists have tried to explain how females choose their mates in most social species.

One of the theories proposed is the sexy offspring hypothesis, which leaves almost no one indifferent with its more than flashy name. Let's see how it explains the process of reproductive selection and how it relates to evolution.

The sexy offspring hypothesis

The sexy offspring hypothesis is one of the best known evolutionary theories, especially because of its particular name. Although its origins go back to Richard Fisher in 1930, as it is formulated today we owe it to Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University, who elucidated their postulates in 1979.

This hypothesis states that the female's selection of a potential reproductive mate takes into account how attractive the offspring will be to her. takes into account how attractive the offspring will be that arise from breeding with one male or another.. Thus, if the male offspring are attractive, when they grow up, they will be chosen by other females, which will result in the genes of the first female being passed on from generation to generation.

Within the theoretical framework of the sexy son hypothesis, more importance is given to an indirect factor, such as the aesthetic beauty of the potential mate, rather than more direct aspects such as territorial dominance, physical strength or longevity. The female is more interested in having many offspring than in having offspring and grandchildren that are strong.

The female chooses, the species evolves

Ever since evolutionary biology was formulated, the idea has been advocated that one of the fundamental factors in the survival and evolution of a species is how its females select the most desirable males.

In relation to this, Richard Dawkins, in his famous book of The Selfish Gene (1976), already defended the idea that in animal species females choose males with the best genes. Males compete with each other to be selected by many females, and females choose one of the best genes. females choose one of them, the best one, to have offspring almost as desirable as their father..

Related to the sexy son hypothesis, if females select physically attractive males, then their sons will be physically attractive as well. This will cause their sons to be chosen by other females as well once they reach adulthood. and, in turn, will ensure that you will have several grandchildren, causing your genetic load to survive and reproduce.

Sexual conflict

As we were saying, females try to choose the best male while males want to reproduce with as many females as possible. In other words, females go for quality while males go for quantity.

Since males are not the ones who, in most species, have to give birth to their offspring, they can fertilize several females in a row, they can fertilize several females in a short period of time, having many offspring of widely varying genetic quality.. Some of these offspring will not reach adulthood, but since there are many of them, there is always the possibility that several of them will reproduce, and thus pass the male genes to the next generation.

On the other hand, females, also in most mammalian and social species, can only have one or two offspring at a time. This is why they choose to look for the male with the best characteristics and, within the hypothesis of the sexy son, the one who is more physically graceful. Their reproductive success depends directly on how attractive their male offspring becomes. If he does not attract other females, the mother's genetic load will not be passed on to the next generation..

It is for this reason that we can understand that the sexual conflict between females and males is different. Males compete to ensure that only one of them is the one that either manages to have the right to reproduce or, in the most violent species, is the one that manages to survive and have intercourse with the females of the group.

Females, on the other hand, compete differently, if at all. They may have to fight to make sure that males notice them, although as most of them tend to go for the maximum amount, it is quite unlikely that they will forget to copulate with any of them.

The good genes theory

Related to the sexy offspring hypothesis is the good genes theory, which is directly related to the fact that females select the best males, but without physical beauty being the only factor. without physical beauty being the only factor taken into account.. Since they can often have only one or two offspring in a short period of time, females prefer that the few offspring they will manage to have have have good characteristics, which will give them evolutionary advantages.

The good genes theory, especially explained for the case of polyandry, proposes that females that find better males, sleep with new ones to ensure that the eggs or ova they have are fertilized with the sperm of the best quality male.

The sexy offspring hypothesis and the good genes theory are related. As with good genes, the sexy offspring hypothesis assumes the existence of indirect genetic benefits that are able to compensate for any directly observable reproductive traits, such as physical strength and parental care, for reproductive success.

The main difference between the good genes theory and the sexy offspring hypothesis is that the sexy offspring hypothesis assumes that this indirect factor is due to the question of how attractive the offspring will be based on sleeping with a particular male. On the other hand, in the theory of good genes reproductive success is taken into account on the basis of the survival of individuals possessing advantageous characteristics for the environment or context in which they are found. for the environment or context in which they find themselves.

Sexy offspring hypothesis in humans

The sexy offspring hypothesis has been extrapolated to reproductive success in the human species. Research indicates that during the most fertile period of the menstrual cycle, women tend to be more attracted to men with traditionally masculine traits, especially being physically attractive and with traits attributable to having been exposed to higher levels of testosterone during fetal development.

In contrast, when the menstrual cycle has subsided and women are less fertile, they tend to be attracted to men with more feminine facial features. It must be said that the studies that have reached these conclusions are quite critical, and these claims are still being disputed.

Physical attractiveness and multiorgasmia

According to research carried out by Oakland University, published in the Journal of Personality and Individual Differencesit was found that the more attractive the man with whom she copulates, the more orgasms the woman tends to have, something that at first might seem obvious.

The fact of having several orgasms when sleeping with an attractive man can be related to the sexy child hypothesis. The woman is much more receptive to an attractive partner, which will make her, in the event of an orgasm, more receptive to an attractive partner.The woman is much more receptive to an attractive partner, which, in the event of having children with her, will make her offspring equally selectable and, in turn, ensure the survival of the woman's genes.

It has also been seen that the likelihood of a female reaching orgasm depends not only on her subjective judgment of how attractive the partner she is having sex with is, but also how attractive the male is viewed by the females in the area.

And why not the sexy daughter hypothesis?

Up to this point, the sexy son hypothesis has been made from the male line of reproduction.. By this we mean that, based on what this hypothesis postulates, the idea of having sex with the most attractive male is to have sons who are also attractive and who, when they reach adulthood, manage to sleep with a high number of women. However, little has been said about having sexy daughters.

Are females also recipients of those genes that would make them as desirable as their brothers, the sexy sons? Is it important for females to be attractive to males, if they copulate with any of them?

According to Drs. Raj Persaud and Peter Bruggen, and taking into account what we have discussed earlier in this article, males, or males in most species, tend to be more concerned with quantity than with quality, being much less selective in their choice of mates.They are much less selective when it comes to choosing a mate than females.

That is why the influence of female genetic load seems to be less decisive for males and, therefore, not having importance how attractive the female is for them.

Bibliographical references:

• Sela, Y. & Weekes-Shackelford, V. & Shackelford, T. & Pham, M. (2015). Female copulatory orgasm and male partner's attractiveness to his partner and other women. Personality and Individual Differences. 79. 10.1016/j.paid.2015.02.008.
• Huk, T., Winkel, W. (2008), Testing the sexy son hypothesis—a research framework for empirical approaches, Behavioral Ecology, 19,(2) 456–461, https://doi.org/10.1093/beheco/arm150
• Weatherhead P. J., Robertson R. J. (1979). "Offspring quality and the polygyny threshold: 'the sexy son hypothesis". The American Naturalist. 113 (2): 201–208. doi:10.1086/283379. JSTOR 2460199.