If the purpose of evolution is to ensure the greatest chances of passing on the genes of a species, then mate choice is surely among the most important aspects of evolution. This essay will analyse the ways in which human mate selection is governed by evolution. Human mate choice is evolutionarily selected for, based upon preferential traits in a mate and strategies for obtaining a mate. Both traits and strategies vary between males and females, as is predicted by evolutionary theory. This essay will analyse questions of culture vs adaptation as an informer of mate preferences, followed by an analysis of adapted traits and strategies for long and short term mating in both sexes.
The inherent assumption in this essay is that human mate selection is based upon evolutionary factors rather than cultural factors and this has proved controversial. One contention is that studies of evolutionary factors influencing mate selection have corroborated western ideals of beauty celebrating female youth and beauty, as well as male wealth and power (Boyd & Silk, 2000). The methodology of investigation into evolutionary tactics for mate selection has been questioned. Much information used to formulate these theories was gathered using surveys, and even when anonymous, people tend to exaggerate or understate their personal experiences (ibid). That human mate choice is informed by evolution is supported by evidence of cross-cultural standards of attractiveness. David Buss (2002), surveyed more than 10,000 participants in 33 countries to ascertain the degree to which mate preferences existed across cultures. His results found the existence of cultural variations in mate selection, notably with regards to the value placed on chastity. Certain traits such as trustworthiness and good health persisted in all studied cultures, however. This cross-cultural persistence suggests the prevalence of underlying evolutionary mechanisms. The remainder of this essay will focus on these cross-cultural traits of attraction.
Many traits linked to beauty and attraction are shared across cultures. Male and female differences in mate preferences are predicted by ‘parental investment theory’ (Boyd & Silk, 2000; Trivers, 1972). This is the concept that while male investment in children is not necessarily high (males do not need to carry children, nor necessarily invest time in raising them), females must make greater investment in their children. For example, females have to invest 9 months prenatally, and a child typically remains dependent upon it’s parents, especially the mother, until late adolescence, (Boyd & Silk, 2000). Therefore, whilst it makes sense for the male to seek females most genetically beneficial to him, with high degrees of fertility (e.g. young and physically attractive), in order to ensure the health of his offspring above all else, it it makes evolutionary sense for females to search for a mate who is more likely to invest in their offspring (Buss, 2006). Males with greater wealth have more to invest and as such wealth becomes an attractive trait to females (Trivers, 1972). Furthermore, the fact that fathers can never be totally certain of paternity is often reflected in in the time spent by fathers investing in their children. Indeed, when adopting children, Fathers will inevitably invest more in children that most resemble themselves, a trait not observed in females (Volk and Quinsey, 2007). Despite differences in parental investment, human fathers invest considerably in their offspring compared to other species (Bereczkei & Csanaky 1996). This conclusion has been criticised however, as studies of female attraction to wealth has generally not taken the female’s own economic status into account. This being said, cases of marriage that is neither hypergamy nor homogamy (females marrying equal to or above their economic station) in industrialized societies is rare (Bereczkei & Csanaky 1996). These desired traits demonstrate the ways in which long-term mate preferences are selected for by evolution.
Buss (2006) observes six evolutionary criteria desired by females in a marriage partner:
- ability to invest resources in her children,
- willingness to invest resources in her and her children,
- ability to physically protect her and her children,
- ability to protect her and her children,
- likelihood of being a good parent
- compatibility of goals and values.
This demonstrates female preference for high standards of paternal investment. Males, on the other hand, prefer young, physically attractive females. Not only do males tend to marry females younger than themselves, but the age gap grows with each consecutive marriage (Buss, 2006). These long-term mating desires being necessarily informed by initial attraction, preference in mate selection is useless without the ability to identify desirable traits however, and the ability to detect those traits represent evolutionary adaptations in themselves.
Many hormones beneficial to reproductive success produce phenotypic effects, as such, males and females detect for hormone markers indicative of reproductive fitness. These often translate to cultural standards of beauty. Females are shown to be attracted to males with high testosterone levels. (Fink & Penton-Voak, 2002) This may be because testosterone is an immune-suppressor, meaning males with high levels of testosterone who are still healthy, must have a strong immune system. Testosterone presence has phenotypical effects, namely larger muscles and greater definition in the cheekbones and jaw. Large musculature could reasonably be attributed to a variety of other survival traits, but well-defined facial features are well supported as an adaptive trait for mate selection (ibid.) Likewise, males are attracted to smoothe skin in females as it indicates high estrogen levels (ibid.
Perhaps the greatest evidence for evolutionary adaptation of phenotypes for mate selection comes from the variability of traits desired by females. This has been linked to the menstrual cycle. When a female is ovulating, she is more attracted to males with masculine features, as the chance of conception, and hence a healthy offspring, is high. When not in this state, she is more attracted to males with more feminine features, as this is observed to be an indictor of willingness to invest in offspring (Fink & Penton-Voak, 2002; Pawlowski and Dunbar, 1999).
Mating strategies, especially in short term mating, support evolutionary theory particularly well. Although males and females claim differing ideals in the number of mates they desire (on average males claim to desire 18 partners over their lifetime, the female average is 4.5), both males and females engage in short-term mating. Males have vastly lower standards in short-term mating, and are far more likely to accept invitations of casual sex (Buss, 2006). The reasons females engage in short-term mating is confusing to evolutionary psychologists given the potential risks of pregnancy. Several hypotheses seek to address this. Theories with large amounts of evidence include Mate Switching (finding a genetically superior mate during ovulation) and Mate Expulsion (more easily leaving a failing relationship). Other hypotheses with moderate support include the Vengeance Hypothesis (vengeance for infidelity) and the Resource Accrual Hypothesis (receiving gifts from a short-term mate) (Greiling & Buss, 1999).
Jealousy is considered an evolutionary adaptation as a form of mate guarding, and corresponds to the risks of male and female mating. That is, 61% of males considered sex to be the most objectionable aspect of infidelity, compared to only 13% of females, whereas 81% of females considered emotional attachment to be the most objectionable compared to 39% of males. This shows that males attempt to reduce paternal uncertainty, whereas females look to reduce the risk of a lack of investment in offspring from the male. This has varying effects in behavioural output. Males engage in mate-retention strategies when their mate is young and sexually attractive, whereas females engage in mate retention tactics when their mate has a high-income job and devotes a lot of time to improving his social status. Tactics for mate retention vary from “vigilance to violence” (Buss, 2006) Female mate retention strategies tend to include increasing their own physical appearance, and intentionally invoking jealousy within their mates. Male retention strategies tend to include the presentation of resources, and threats of violence against potential rivals (Buss, 2006).
In reality, human mate selection is rarely so simple. We do not all marry the richest males or most sexually attractive females we meet. Pawlowski and Dunbar (1999) describe this in terms of optimal foraging. People select mates in competition with one another, therefore their criteria in searching for a mate vary not only upon the factors described above, but also on their own perceived levels of attractiveness.
In conclusion, human mate choice is selected through a male’s preference for females indicated to have the greatest reproductive viability, and a female’s preference for males ablest to acquire resources, and therefore more likely to invest in potential offspring. Despite this evolutionary preferences, humans are competing for the resources of the other sex, and therefore use principles of optimal foraging to attract the most viable mate they can find. This is not the entire story., however. For example, this essay has considered only heterosexual relationships. Homosexual relationships, not involving procreation, may select mates based on separate criteria, perhaps involving fitness for roles as caregivers, as observed by Vasey and Van der Laan (2010). Additionally, traits regarding mate preference varying among culture have not been reviewed. A complete analysis of the evolutionary adaptations for mate selection would therefore require a more in-depth analysis than this essay allows for.