Sexual Selection as a Specific Form of Natural Selection

Introduction

Sexual selection is a controversial term due to its definition. Sexual selection can be viewed as an independent type of selection; separate from natural selection. However, others view sexual selection as another form of selection under natural selection. These views originate from the discoverers of natural selection: Charles Darwin and Alfred Russel Wallace. Even though they both agreed upon the ideals of natural selection, both Darwin and Wallace argued about the definition of sexual selection. This was an ongoing dispute until Darwin’s death; giving Wallace the upper-hand over the argument on sexual selection. Wallace had become successful in defining sexual selection; silencing Darwin’s view of sexual selection. Darwin’s view remained silent as Wallace’s view was widely accepted over Darwin’s. However, Richard Prum, author of The Evolution of Beauty, argues in favor of Darwin’s ideas instead of Wallace.

What is Sexual Selection

Sexual selection is a type of selection where species choose who they mate with. Based on Darwin’s view, there are two forces: intersexual; the struggle between male to male competition, and intrasexual; females being the prime mate choosers. He also believed that the standards of beauty (ornamental) and armament traits coevolved together. He claims that a being needs to be attractive enough to find mates to reproduce with, while also being able to survive to reproduce. Being a creationist, Wallace disagreed with Darwin. Wallace believed that sexual selection was an explanation for being another form of natural selection. He asserted that female mate choice directly linked to the survivability of a male and not display traits (Andersson 1994).

Sexual Selection Among Humans and Non-Human Primates

Sexual selection between humans and non-human primates differ due to the complexity of human evolution. A significant difference is the frequency of mating system between both populations. In a modern human society; monogamous relationships are the most common type of mate choice (Kinzey 1987). This allows more parental investment for offspring because most species that follow the monogamous mating system; tend to have longer gestation periods and less offspring per birth. On the other hand, monogamy is rare amongst non-human primates, while polygamous mate choice is more common. Non-human primates that follow the polygamous mating system tend to have more offspring overall but have less paternal involvement compared to primates following the monogamous mating system. Both mating systems have their own issues: individuals fighting for a single mate in monogamy, and individuals fighting amongst each other within a group to gain access to the sole mate in polygamy. However, both mating systems can persuade male primates to commit infanticide. Contemporarily; infanticide is deemed immoral and criminal in most human societies. Since there is no criminal structure within non-human primates, their morals can vary. This allows them to partake in infanticide as they wish. Another issue that is common between the two mating systems is sexual coercion. Even though sexual coercion does not fit under sexual selection, it is significant among mate choice. Those who commit sexual coercion can be seen as unattractive. Sexual coercion is favorable for humans as there are punishments for committing rape. As for non-human primates, the lack of a criminal system allows males to sexually coerce females without punishment. It is common among males to partake in sexual coercion to ensure females produce their offspring. Male chimpanzees commonly rape female chimpanzees to ensure their offspring will be produced (Gray 2013). However, sexual coercion amongst humans is deemed immoral and can lead to severe punishment depending on a criminal’s residing country. A formal judiciary structure and morals favor individual mate choice for humans; whereas non-human primates are left to defend themselves.

Technology in humans is superior compared to non-human primates to the point where contraceptives prevent human pregnancies. This allows humans to engage in sexual intercourse for pleasure and discards the fear of unwanted pregnancies. Unlike humans, there are non-human primates are incapable of creating contraceptives, rather humans have created contraceptives for them. Therefore, most non-human primates do not have access to contraceptives and can partake in sexual intercourse; with a high possibility of becoming impregnated. Having sexual intercourse for pleasure is a trend among living species including humans. These trends can help distinguish more about human evolution; we can correlate similar behavior between humans and other species. One significant trend is shifting from intersexual selection; to intrasexual selection.

Trends in Human Evolution

Sexual selection among birds can help determine trends in human evolution. For example, ducks have a desire to be in sexual relationships with female ducks who have autonomy (Prum 2017). In a sexual relationship between humans, there is no relationship if an individual, mainly females, do not have autonomy; that is the right to make independent choices. This trend is that both partners of a sexual relationship are willing to be with each other; instead of an individual being forced to be with one another. Another example given by Prum would be the Great Argus; females are attracted to males based on appearance and ornamental traits (Prum 2017). This trend of those who have a better appearance will have access to more mates that can be true for humans. However, appearances are not the only factors of what makes an individual attractive. Humans can be: socially attractive, intellectually attractive, emotionally attractive, physically attractive, or even financially attractive. Sexual selection amongst humans becomes more complex as we evolve further away from non-human primates. We can expect humans to focus on the standards of beauty over surviving in general.

Shift from Intersexual to Intrasexual

The benefits of sexual selection are access to resources, a shelter for protection, and increased parental care. For most hominins, males are the sole providers for resources while females tend to their offspring. If females are the ones who carry offspring during gestation periods and invest more time on their infants; then their autonomy should be considered against males (Tanner & Zihlman 1976). Females are found where abundant resources are, and males are found where the females are at. If males provide the resources, then females get to choose which male they prefer. Males who have access to more resources have more armament traits than ornamental traits. When resources become too abundant, females are given the choice to choose a mate over their appearance rather than their ability to survive. Humans are a prime example of this as survival of the fittest has no significance in our contemporary society.

Ideally in the past, women were expected to stay at home and tend to their infants while the men became the breadwinners at work. Now, the idea of a woman being as equal as a man is present in many, but not all societies. Because resources have become plentiful for humans, females no longer have to choose mates regarding a higher chance of survivability. Again, they are given the option of choosing mates that are either: socially, financially, intelligently, or emotionally attractive. Surviving to reproduce is not a common issue among humans, so humans can consume more effort in their appearance. The shift from survival to beauty enables females to focus on their appearance as well; that is if the female is not struggling to survive financially.

Since human evolution is continually evolving and is complex compared to other non-human primates, we can expect higher standards of beauty over time. This is only possible if the individual lives above poverty and has a decent standard of living; meaning that they are not struggling to access basic necessities (food, water, and shelter). Shifting from survivability to beauty would result in an increased emphasis on taking care of personal hygiene. Men will do whatever it takes to attract a female. Additionally, there are many different preferences that a female holds. A variety of preferences creates a diversity of mates to choose from. This is why human evolution offers a variety of individuals within one species.

Summary

There has been controversy Charles Darwin’s view of sexual selection; against Alfred Rusell Wallace’s view. Russell asserted that if Darwin was true, display traits would only evolve if they were linked to adaptations. Sexual selection differs among primates mainly based on mating systems. Monogamy is common among humans, while polygamy is more common among non-human primates. Humans can be punished for committing immoral acts; however, non-human primates don’t have a criminal system that influences their morals. This enables them to commit infanticide and sexual coercion without punishment. Many species partake in sexual intercourse for pleasure; however, humans are the only species that have developed contraceptives to prevent unwanted pregnancies. Sexual intercourse for pleasure is amongst many trends between non-human species and species that help identify more trends in human evolution. We can find select examples from birds to identify trends in human evolution. Trends include the shift from intersexual to intrasexual. Females have the right to choose their mates based on ornamental or armemental traits. Since resources have become abundant for humans, females can focus mate choice based more upon the appearance, rather than the ability to survive. This has lead to an overall shift of focusing on appearance rather survivability. Preferences to mate choice will further evolve, and so will the number of diverse individuals for humans.

References

1. Andersson, M. 1994 Sexual Selection. Princeton (NJ): Princeton University Press.
2. Gray, P. B., & Garcia, J. R. 2013 Evolution and Human Sexual Behavior. Chicago (IL): Harvard University Press.
3. Kinzey, W. G. 1987 Evolution of Human Behavior: Primate Models. Albany (NY): SUNY Press.
4. Prum, R. O. 2017 The Evolution of Beauty. New York (NY): Doubleday.
5. Tanner, N., & Zihlman, A. 1976 Women in Evolution. Part I: Innovation and Selection in Human Origins. Chicago (IL): The University of Chicago Press.