9.1.1 Sexual Selection

• Evolutionary explanations of behaviour are based on the idea that human beings seek to continue their genetic line using the mechanisms of adaptation to ensure their survival (achieved via reproductive success)
• Traits are passed down from generation to generation with only the fittest traits surviving this process: in terms of sexual selection this would mean selecting a partner who is likely to give your offspring the best chance of survival and further reproduction
• The evolutionary explanation of sexual selection is based purely on opposite-sex attraction (as, until fairly recently, it was only possible to reproduce via traditional sexual intercourse)
• The traits which are deemed attractive by males and by females are quite distinct and have different functions according to evolutionary psychology

• Inter-sexual attraction refers to the differences between males and females and the ways in which these differences manifest themselves as attractive qualities in a mate
• Inter-sexual attraction can be seen vividly and obviously in animal mating patterns e.g. the male peacock’s display of colourful feathers to attract a female; the zig-zag dance performed by male sticklebacks to attract the attention of fertile females
• These examples of male display and female fertility are not so marked in human beings but some parallels can be drawn between animal inter-sexual selection and that attributed to human beings as follows:
  • Human males who are wealthy give a ‘display’ of their wealth via expensive cars, houses, yachts, watches etc.
  • By displaying his wealth the human male is telling interested females that he has resources i.e. he can support her and any children she may bear him
  • Human females who are fertile tend to be young (menopause signals the end of fertility around the age of 40)
  • Female physical attributes which signal fertility are a desirable waist-to-hip ratio (the ideal is 0.7 in Western cultures); generous hips (for child-bearing); ample bosom (for breastfeeding) and all-round good health e.g. long, shiny hair, clear skin, bright eyes
  • In short, males must have resources to offer security to the female; females must show that they are a good ‘investment’ in terms of their child-rearing potential
• One of the main features of inter-sexual selection is female choosiness which is the concept that females must exercise much more caution and wariness when choosing a sexual partner than males need to
• One of the main explanations for female choosiness is anisogamy - the idea that ‘sperm is cheap; eggs are expensive’ i.e. men can produce billions of spermatozoa per day whereas a woman will produce only one egg per month
• What the above points boil down to is that females must take care not to have sex with ‘just anyone’ as the result could be pregnancy: the female may be saddled with a partner who lacks sufficient resources (males can have a lot of sex and never get pregnant so the same conditions do not apply to them!)

Do you still think inter-sexual selection is a myth?...

• Intra-sexual selection refers to the ways in which one sex competes for the attention of the opposite sex
• Competition takes place between males for the attention of females (according to evolutionary psychology females do not need to compete for male attention as the assumption is that males desire lots of females: quantity, not the quality desired by females)
• The obvious physical and psychological attributes a male should possess in order to triumph over his rivals and find reproductive success include:
  • Height
  • Muscles
  • Physical fitness
  • Aggression
  • Competitiveness
  • Risk-taking
• As females do not need to physically compete for males’ attention they have evolved to be smaller, less muscular, have less physical strength (physical dimorphism) and to be less aggressive and competitive

A competitive woman? Surely not!

Research which investigates evolutionary partner preferences

• Buss (1989) - a cross-cultural survey conducted over 33 countries which found that females prefer male partners who have resources and traits such as ambition whereas males prefer younger female partners who are attractive and fertile
• Clarke & Hatfield (1989) - a field experiment in which female and male students were asked  to ‘go to bed with’ an opposite-sex stranger (of the same age and deemed to be ‘attractive): 75% of the males said yes to this request; not one of the females did
• Ronay & von Hippel (2010) - a field experiment in which male skateboarders took greater physical risks when in the presence of an attractive female

Evaluation of Sexual Selection & Evolutionary Partner Preferences

Strengths

• There is some validity to this theory as seen in research findings such as Buss (1989) cited above and in anecdotal evidence derived from real-world observations of male-female mating behaviour i.e. it is more common to see a rich, older man with a much younger woman than vice-versa
• Research by Daly & Wilson (2001) supports the idea that young men who live in dangerous neighbourhoods with a high homicide rate are more likely to take risks and put themselves in danger in order to attract women (i.e. to pass on their genes while they are still able to do so)

Weaknesses

• The theory lacks external validity as it does not account for variations in mating preferences e.g. women are actually able to support themselves and do not necessarily need to rely on a man; some men do not focus on physical attractiveness above all else when looking for a female mate
• Evolutionary theory is solely concerned with heterosexual mating preferences and reproduction which means that it has limited applicability to homosexual people and to the LGBTQ community as a whole

Link to Issues & Debates: 

The ideas that underpin this theory are extremely reductionist in that they condense complex human behaviour such as sexual selection into a binary dynamic minus any nuance or variability. The reductionist nature of this argument can be (and has been) used by people (mainly men it has to be said!) to push a sexist agenda in which women are reduced to baby-makers who are obsolete after a certain age and men as the human equivalent of bank accounts. An evolutionary approach to sexual selection also legitimises the view that men can have sex with as many women as they like whereas women have to be circumspect in their sexual encounters, only having sex with men who they are likely to commit to.

Evolutionary theory falls firmly on the side of nature in the nature/nurture debate with its emphasis on innate drives.

Link to Approaches: 

Evolutionary explanations of behaviour reside within the Biological Approach for the reasons outlined above: their emphasis on innate drives and behaviour that has adapted across generations.