Mate choice

Mate choice is the process of how one sex animal selects specific traits in another sex animal for purposeful and successful mating and production of offspring. In the animal kingdom, reproduction behavior propagates the continuation of a species, and thus is an important topic to understand. Since the nineteenth century, scientists have studied the mating process of thousands of animal species to understand how they choose their mates. Depending on the species, mate choice behaviors differ in both males and females. These behaviors are determined by many factors, including instinct, availability of choice, evolutionary processes, and the environment. Although the study of mate choice has been a biological topic for more than 150 years, the study of mate choice in humans is inconclusive and provocative. Human partner choice involves measuring the psychological and sociological aspects of partner behavior, which in turn is defined by cultural, religious, and economic perspectives, among other considerations.

Background

Charles Darwin’s revolutionary 1859 work, On the Origin of Species by Means of Natural Selection, introduced the theory of evolution and sparked conversation about the existence and continuation of life. It also laid the foundation for later scientific studies in understanding the dynamics of mate choice. According to Darwin, animal sexual selection is determined in two ways: by male-to-male combat called intrasexual selection, or by a female’s choice from a set of attractive males called intersexual selection, the latter otherwise known as mate choice. According to Darwin’s theory, males combat each other to prove prowess and strength. Champions of the battle mate and pass along their genes, thus strengthening the species through the evolutionary process. His theory also includes the stance that before an animal chooses a mate, he or she first evaluates traits that will promote success for procreation. The choosing mate can either be male or female. These traits include attractiveness, increased territory, quality of territory, the ability to protect, and the ability to help care for the offspring. Because these traits propagate the species, they are naturally selected through the process of evolution promoting the survival of the fittest. In a subsequent book in 1871, The Descent of Man, and Selection in Relation to Sex, Darwin applied his evolutionary theory to humans and, specifically detailed his theory of human sexual selection by addressing how mate choice evolves, and what factors determine the intensity of mate choice in each gender.

In Ronald Fisher’s 1930 book, The Genetical Theory of Natural Selection, he explained the runaway theory involving a variety of animal species. It supported Darwin’s evolution theory that female preferences, over time and through natural selection, transformed male features. For example, female peacocks desire a male that has a full beautiful plumage. Over time, this trait will increase in males, because male peacocks with colorful plumage will have more reproductive success. Other examples of mate choice that induced evolutionary characteristics were the mane of a lion, the large tusks of male narwhales, the enlarged proboscises of the male elephant seal, and the bright facial and rump coloration of the male mandrill.

Angus John Bateman introduced his principles in 1948 in the paper “Intra-Sexual Selection in Drosophila.” In studying the fruit fly genus Drosophila, Bateman explained that variability in reproductive success is greater in the male fly than in female flies since males are capable of producing millions of sperm cells. Females harvest a small number of eggs at the cost of expending large amounts of energy, and according to this theory, indicates the female’s role is significantly larger in the production of an offspring. Since females are the limiting factor, males will therefore compete with each other in order to find a mate.

In 1972, Robert Trivers introduced the parental investment theory. He suggested that many factors (varying in every species) help to determine which sex will make the greater parental investment. Usually this is the female who produces only one egg at a time, becomes impregnated, and is responsible for nursing. Because of this, the behaviors employed by males and females to choose their mates differ greatly. Again, this supports what Darwin and his successors have concluded, that males simply try to mate with as many females as possible while females search diligently for a good parental supporter before they mate.

Overview

Although much research has been analyzed and theorized about animal mate choice, the factors governing human mate choice remain obscure and complex. If animal mate choice theories are applied to human mate choice, at the least, it can be concluded that the choices made by cultural ancestors over thousands of centuries have helped evolve into specific cultures today. According to Brendan P. Zietsch and his colleagues, several studies have been conducted on human mate choice.

In one series of studies, it was determined that romantic partners primarily choose partners based on closeness of age, social attitudes, and religious beliefs and only moderately on general intelligence, education, and physical attractiveness. These studies show that height, weight, and personality traits are not primary concerns. In addition, another group of studies theorizes that people use assortative mating, or seeking out a person with an important similar trait, to choose a mate. Assortative mating is partly due to a similarity in social backgrounds. Since those with similar social backgrounds converge naturally in communities, this provides opportunities to encounter those that have similar traits. This differs from previous studies that indicate mate choices are specifically made to benefit the offspring.

Another series of investigations have established that genetic factors such as physical (attractiveness, size, height, weight, and eye color) and behavioral characteristics (personality traits, social skills, and religious beliefs) are preferred over other traits. Some studies even indicate that females use the sense of smell to choose a mate.

An analysis of speed dating shows that self-reported mate preferences have little connection to actual choices. This phenomenon is theorized by another study showing that a limited mating market shrinks the opportunities for mates to adhere to their own mate preferences. This is more pronounced especially when seeking a more permanent lasting relationship. In fact, most studies that have addressed mate selection preferences cannot conclude that the mate preferences relate to the formation of long-term partnerships.

Societies define population-wide mate preferences, such as genetic quality, parental investment, and respectable social standing, because those preferences maintain high evolutionary standards. Yet not all humans use these preferences in making their mate choices. Another aspect of mate choice deals with why variations occur. Parents are individuals, even though some traits were identified as compatible. This makes the partnership an individual pair. This accounts for some variation in the offspring, but further research is needed to fully understand the cause of this variation.

Variations can be genetic or non-genetic. An example of a non-genetic factor is parental influence, or the influence parents instill in their children’s decision in choosing a mate. Another theory of variation includes the idea that during formative years, a child will develop mate choice criteria by using his or her opposite sex parent as a model for desirable traits. This is called sexual imprinting.

Heritability refers to the proportion of variation due to genetic variation. By studying sets of identical twins and non-identical twins and their spouses, researchers looked to see if the twins selected mates with the same personality traits. The correlation between the choices of partners of both types of twins was weak. In a second study, researchers also used identical and non-identical twins but analyzed the mate choices based on traits including height, weight, income, education, social attitudes, and personality measured by Eysenck’s scales, which assess the personality traits of people. Higher correlation of these traits in the partner choices of the identical twins was found, showing that genetic and environmental factors affect heritability. However, these two studies have divergent results.

Although there have been years of study on human mate choice, conflicting research has caused confusion and disagreement. The perplexity of mate choice perhaps causes people to simplify it, and this has a profound effect on social, economic, religious, and political domains of society. For instance, the fashion industry has capitalized on visually attracting the opposite sex through the use of clothing, jewelry, and fragrances. The advertising industry exploits human physical characteristics, sometimes provocatively, to sell products. Weight management companies and plastic surgeons take advantage of the human need to be sexy and beautiful. The way Internet dating sites design their customer profiles affect mate choice criteria. Social media limits face-to-face interaction, perhaps changing criteria for mate choice. As society accepts the emphasis on multiculturalism, mate choice will inevitably change based on culture and religious intermingling. The current acceptance of how sexual identity is determined and labeled will most certainly define mate choice differently. Human behavior will adapt to the social, economic, religious, and political demands, which will open up a whole new area for mate choice study.

Bibliography

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