Sexual Selection

Darwin proposed that species do not just evolve through Natural selection but also “Sexual Selection”– A view that competition for mates between individuals of the same sex affects the evolution of certain traits. Any physical trait that enhances reproductive success will gradually be passed down and enhanced over evolutionary time. 

Darwin proposed that animals possess features that make them attractive to members of the opposite sex and allow them to compete better with members of the same sex for example male peacocks have colourful feathers to attract their mates. Darwin came up with his theory for sexual selection by describing to processes, Intrasexual selection (mate competition) and Intersexual selection (mate choice). 

Intrasexual selection is when members of one sex (usually males) compete with other members of their own sex for access to members of the opposite sex (mate competition) Whatever traits lead to success in this competition will be passed on to the next generation. 

Intersexual selection is when members of one sex (usually females) show preferences for members of the opposite sex who possess certain characteristics (mate choice). These indicate the chances of the mate being able to give protection and support to offspring which makes them more attractive as a potential mate. 

Different sexual selection pressure occurs between the genders due to differences in gametes (Eggs & Sperms). Males have millions of sperms however can never be certain of paternity and suffer little cost to reproduction therefore natural selection favours them maximising their mating opportunities. 

Females however have a limited number of eggs with each representing a huge investment during and after pregnancy but are certain of paternity. Due to this they must be choosier in finding strong, healthy and committed males with resources.

Buss et al conducted a cross-cultural study over 37 cultures with over 10’000 people on mate preference. Males reported to prefer younger physically attractive females while females sought physically strong and athletic males with an emphasis on resources.

Both are therefore engaging in behaviour that increases reproductive success supporting sexual selection theory. The main issue with this research was that questionnaires were used which can be easily miss-understood across cultures. Also self-reports may be inaccurate as well as translation problems occurring through the use of third party translators. 

Also mate preference may not be indicative of what actually happens either in real life. Studies like Buss’s survey of mate choice might suffer from validity- as they give us an indication of expressed preferences rather than being a reflection of what actually happens in real life. 

However, many real- life studies also support these mate- choice hypotheses. For example, a study of actual marriages in 29 cultures (Buss 1989) confirmed that men do choose younger women. It found that men who divorce and remarry tend to marry women who are increasingly younger than they are. 

This shows that from an evolutionary approach men are still looking for women to give them offspring so would choose younger females as they would be more likely to carry their offspring than older women as less problems would arise e.g. older women go through the menopause at ages such as 40 and older so would be unable to have any more children.

Psychologists propose it is this evolutionary behaviour that then shapes mate selection in males and females. Males should in theory look for females showing signs of fertility, youth and physical attraction and females should seek males showing signs of genetic strength, masculine features and the ability to provide and protect. 

The importance of fertility is high in mate choice, in most mammalian species the female gives out a variety of visual or chemical signals, which encourage the male to mate. In human females, however, oestrus is hidden, although some research suggests that women near their most fertile point of their menstrual cycle are more attractive to males. A recent study in the US confirmed this, researchers calculated the tips earned by lap dancers at varying stages of their menstrual cycle.

Those girls who were in the fertile oestrus phase of their cycle earned almost twice the value of tips compared to girls who were not in oestrus (Miller et al 2007). But this study has many problems, it took place in the US so cannot be generalised to other cultures, as many cultures may not have a high number of lap dancing clubs or in some tribes wouldn’t even have such things.

There could also be a large number of extraneous variable present, such as certain men may be regulars and visit a particular women and in the time of the study could have come more or less often which would have changed the results which would reduce the validity of the results. The dancers themselves could guess the experiment and change their behaviour causing demand characteristics this would reduce the reliability of the results. 

The area in which the clubs were could have a big impact as the wealthier the area was could lead there to being more tips given to the women by the men whether they were attracted to the women or not.

Although such studies outline the preferences individuals have they are not representative of what actually happens in real life. Many variables play a role such as social or cultural factors as well as the opportunities available for both genders within their social circle that are not factored in. 

Evolutionary theories such as this can be argued to be reductionist as they simply put down mate choice due to our genetic makeup. In truth partner choice is much more complex involving cultural and social elements which are not fully considered and this theory portrays us as driven purely by nature which is clearly not true. 

The theory is also deterministic as it suggests human sexual preferences are genetically programmed and we are at their mercy. The theory does not take into account our ability of conscious thought which gives us free will to make choices for ourselves. Even in Buss et also study across cultures “Kindness” and “intelligence” was ranked higher than physical attraction.     

Sexual selection theory cannot also explain homosexuality and why this exists. No children are produced and such behaviour goes against the theory. As one of the big reasons we have Inter and Intra-selection is to carry on our genes and to produce offspring which is something homosexual couples can’t do, in most cases these couples have one genetic parent and one donor parent. This raises serious ethical issues as people may use sexual selection theory to highlight the “abnormality” of homosexuality and create prejudice through homophobia.