The sexy son hypothesis: explaining sexual selection

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

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

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The sexy son hypothesis

The sexy son hypothesis is one of the best-known evolutionary theories, especially by its particular name. Although its origins date back to Richard Fisher in the 1930s, As it is formulated today we owe it to Patrick J. Weatherhead and Raleigh J. Robertson from Queen University, who clarified their postulates in 1979.

This hypothesis states that the selection of a potential reproductive partner by the female she takes into account how attractive the children that arise from breeding with one male or another will be

. Thus, if the male children are attractive, when they grow up, they will be chosen by other females, which will cause the genes of the first female to pass from generation to generation.

Within the theoretical framework of the sexy son hypothesis, more importance is given to an indirect factor, such as beauty. aesthetics of the potential partner, rather than more direct aspects such as their territorial domain, physical strength or longevity. The female cares more about having many offspring than having superior children and grandchildren in terms of strength.

The female chooses, the species evolves

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

In relation to this, Richard Dawkins, in his famous book on The selfish gene (1976), already defended the idea that in animal species females choose males with the best genes. The males compete with each other so that many females select them, and the females choose one of them, the best one, to have children 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 children to also be chosen by other females once they reach adulthood. and, in turn, will ensure that they have several grandchildren, making their genetic makeup survive and reproduce.

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The sexual conflict

As we were already saying, the females try to choose the best male while the males want to reproduce with the maximum number of females possible. That is, 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 children, they can fertilize several females in a short period of time, bearing many offspring of highly variable genetic quality. Some of these children will not make it to adulthood, but since there are so many, there is always the possibility that there are several of them who do manage to reproduce, and thus pass the male genes to the next generation.

Instead, females, also in most mammalian and social species, can only have one or two children at a time. It is for this reason that 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. Your reproductive success directly depends on how attractive your male child 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 between males is different. The males compete to ensure that only one wins the right to reproduce or well, in the most violent species, it is the one that manages to survive and manage to have intercourse with the females of the cluster.

The females, on the other hand, their competition is different, if there is one. They may have to fight to make sure the males notice them, though like most they tend to for the maximum amount, it is highly unlikely that they will forget to mate with any of they.

The theory of good genes

Related to the sexy son hypothesis we have 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 taken into account. Since they can often only have one or two children in a short period of time, females prefer that the few children that they will manage to have have good characteristics, which will bring them advantages evolutionary.

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

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

The main difference between the good gene theory and the sexy son hypothesis is that the sexy son hypothesis assumes that this indirect factor is due to wondering how attractive the children will be based on sleeping with a certain male. On the other hand, in the theory of good genes reproductive success is taken into account based on the survival of individuals because they possess advantageous characteristics to the environment or context in which they are found.

Sexy son hypothesis in humans

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

In contrast, when the menstrual cycle has already subsided and women are less fertile, they tend to be attracted to men with more feminine facial features. It should be said that the studies that have reached these conclusions are quite critical, in addition to the fact that these statements are still being discussed.

Physical attractiveness and multi-orgasmia

According to research conducted by Oakland University, published in the Journal of Personality and Individual Differences, it was seen that the more attractive the man she has sex with, the more women tend to have orgasms, something that at first might seem obvious.

The fact of having several orgasms when sleeping with an attractive someone can be related to the hypothesis of the sexy son. Women are much more receptive to an attractive partnerof her, which will make that, in case of having children with her, this offspring is equally selectable and, in turn, guarantees the survival of the woman's genes.

It has also been seen that the possibility of a female reaching orgasm does not depend solely on her subjective judgment of how attractive she is. is the partner with whom he is having sex, but also how attractive the man is seen by the females of the zone.

And why not the sexy daughter hypothesis?

So far, the hypothesis of the sexy son has been made from the male line of reproduction. By this we mean that, based on what this hypothesis postulates, the idea of ​​having sexual relations with the most attractive male is to have attractive male children and that these, 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 desirable like their brothers, the sexy sons? Is it important that the females are attractive to the males, if they also copulate with any of them?

According to doctors Raj Persaud and Peter Bruggen, and taking into account what we have previously discussed in this article, men, or males in most species, tend to care more about quantity than quality, being much less selective when choosing a partner compared to women or females.

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

Bibliographic references:

• Sela, Y. & Weekes-Shackelford, V. & Shackleford, 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.