Sexual Selection

Human Reproductive Behaviour: Psychology

Sexual selection refers to the evolutionary explanation describing why humans prefer some partners over others. Sexual selection is deeply rooted in the evolutionary approach and, therefore, explains sexual selection in terms of survival and reproductive success.

In theory, those who exhibit certain characteristics within a population, which allows them to better find a partner to reproduce with, have a reproductive advantage over others.

What traits are deemed desirable varies across cultures and societies. Due to the increased chances of finding a partner, these features have an increased chance of being passed down to children.

In line with the sexual selection definition, human reproductive behaviour is part of adaption, and therefore, individuals look for certain characteristics in their potential partners.

Types of Sexual Selection

The types of sexual selection emerge based on the strategies that women and men engage in regarding sexual selection. There are two types of sexual selection: inter-sexual selection and intra-sexual selection.

We can see inter-sexual attraction in some animal species.

Now, let's explore intra-sexual selection.

Intra-sexual selection may also explain physical differences between men and women. Some theories postulate that men are generally stronger and bigger as they need to maintain evolutionarily desirable characteristics to be selected by women (if men were bigger and stronger, they are more likely to survive and provide).

On the other hand, women choose mates to protect them and therefore do not need to have such traits to enable them to survive or reproduce. Instead, they develop traits desirable to the opposite sex.

Fig. 2 - Women and men develop differently according to their needs.

In 1989, psychologist David Buss surveyed the sexual selection and reproductive behaviour of over 10,000 adults' in 33 countries.

• He found that females placed more importance on resource-related characteristics such as ambition, high intelligence, and good financial prospects.
• In contrast, men preferred younger partners and placed more value on attractiveness and modesty, values that reflected a woman's ability to reproduce.

Similarly, Clark and Hatfield (1989) investigated differences between male and female reproductive behaviour on university campuses.

• They asked male and female students to approach the opposite sex and ask various questions, including propositions such as 'Will you go to bed with me tonight?'.
• They found that whilst the vast majority of men agreed to a sexual liaison, no women said yes.

The study supports the idea that women are much more selective and engage in inter-sexual selection (carefully picking mates), whereas men are intra-sexual (picked by women).

Sexual Selection Example

The two types of sexual selection strategies described above can be seen in the Andean cock-of-the-rock bird. These birds are found in South America and are very colourful.

Their sexual selection strategy is very well-defined.

• When the female needs to choose a partner to mate with, males take part in communal leks. In a lek, males face one another and perform a confrontational display. Males are not actively fighting but rather are engaging in choreography.

• During the lek, the males face each other and bow, jump and flap their wings. The lek becomes more intense when the female gets closer, and males may even grunt at one another.

This is an example of how intra-sexual selection takes place through two birds competing against one another. The inter-sexual selection strategy involves the female watching how the males engage in the lek.

Fig. 2 - The cock-of-the-rock bird engages in sexual selection.

Relationship between Sexual Selection and Human Reproductive Behaviour

The relationship between sexual selection and human reproduction has been widely explored in psychological literature.

Some of the literature has focussed on physical attractiveness. Physical attractiveness refers to what individuals find physically appealing about the person. Although there are individual differences in physical attractiveness, there is some consensus on what individuals find attractive.

• This is because physical traits that are perceived attractive are usually a sign of fertility and generic fitness.

Waynforth and Dunbar (1995) also conducted a study on attractiveness.

• They reviewed 'Lonely Hearts' columns in American newspapers and found that men advertised their resources and intelligence whilst women described themselves in terms of physical attractiveness and youth.

The study demonstrates how males and females display their traits to potential partners and identify characteristics they deem most desirable to the opposite sex.

Further evidence of the relationship between sexual selection and reproduction comes from Buss' (1995) study in which he explores jealousy in males and females.

• The study's results indicated that women tended to be jealous of emotional intimacy, whereas men feared sexual intimacy. Buss stated that this supports biological explanations of reproductive behaviour as men fear sexual intimacy more due to the possibility of a woman having another man's child.

• On the other hand, women fear emotional intimacy as this puts their security and resources at risk.

Differences between Sexual Selection and Human Reproductive Behaviour

As we discussed above, males and females tend to have different choices when it comes to sexual selection. As a result, this has a direct impact on reproductive behaviour. Sexual selection is the prelude to reproductive behaviour; sexual selection identifies the best candidate to mate with, affecting human reproductive behaviour.

Women will seek strong, independent, high-resource men to secure their futures and increase their chances of survival, and men will seek attractive, youthful women to increase their chances of reproducing. This may affect short-term and long-term partner choices.

Sexual selection and reproductive behaviour often link back to times when humans were hunter-gatherers.

Interestingly, natural selection and sexual selection can conflict. Features deemed attractive can be linked to lower chances of survival. A male bird with bright feathers, whilst is deemed desirable to female birds, it will naturally stand out and attract predators. However, the increased chances of attracting female attention to produce offspring are worth the potential sacrifice.

Evaluation of Sexual Selection

Buss (1989) supports the theory of sexual selection through their study using questionnaires. They gathered data from 10,000 men and women.

• According to the study, due to limited access to resources, women seek men who can provide these resources, and men seek women who are the most fertile, indicated by their levels of physical attractiveness. Women seek resources, and men value reproductive capabilities.

Singh (1993) also supports the theory with their argument regarding waist-to-hip ratio preferences. Singh (2002) linked the waist-to-hip ratio to health and reproductive abilities.

While the evolutionary perspective has provided extensive research on sexual selection, it is not exempt from criticism.

One of the main arguments that have been provided that question the approach is the presence of gender bias. The sexual selection theory suggests that short-term mating is more common in males. However, this would not be a phenomenon if females were unwilling.

Furthermore, Greiling and Buss (2000) found that women can also show a preference for mate-switching because this encourages the diversity of their offspring.

Furthermore, this theory fails to account for major social and cultural changes which may affect reproductive behaviour.

This means that women do not have to invest as deeply in finding the perfect mate, and men do not have to spread their seed so widely to be sure they have a child. Therefore, nowadays, mate choice is likely influenced by factors other than just evolutionary preferences.

Buss (1989) also identified more similarities than differences in sexual selection. Resources was not deemed as important as mutual attraction and intelligence.