Evolutionary explanations

• What is sexual selection?

  • Attributes or behaviours that enhance reproductive success are passed on through genes, which depends on our chances of survival and our abilities to attract mates
  • Darwin (1871): if a male characteristic enhances reproductive success it will become a preference for females, putting males under pressure to improve that trait
  • Characteristics can include signs of genetic fitness or adaptive traits like aggression in males as it provides an advantage for them over competition for reproductive rights
• What is human reproductive behaviour?

  • Any behaviours relating to the opportunities to reproduce and increase the survival chances of our genes, including mate choice and mate competition
  • Main goal is to reproduce and pass on their genes
• What is anisogamy?

  • The differences between male and female sex cells (gametes)
  • Female gametes (eggs) are larger in comparison, static, have limited years of fertility and invest a lot of time/energy into reproduction
  • Male gametes (sperm) are smaller, extremely mobile, have an infinite supply, and invest little time and energy into reproduction
  • A consequence of anisogamy is that fertile females are a much 'rarer' resource as there is no shortage of fertile males, making sexual selection considerably important for the two genders
• What is inter-sexual selection?

  • The strategies BETWEEN the sexes that males and females use to select each other, preferred by females as they prioritise quality over quantity since ova are rarer than sperm
  • Trivers (1972) pointed out that since the consequences of wrong partner choices are more serious for females, they invest greater time/commitment into selection, ideal mate would be a genetically fit partner willing to provide resources
  • Fisher (1930): 'sexy sons' hypothesis - genes we see today are those that enhanced reproductive success e.g. males with reproductive characteristics pass this onto their sons who then become more likely to be selected by females to mate
• What is intra-sexual selection?

  • The strategies WITHIN each sex to be the one that is selected, preferred by males
  • Competition between males to be selected to mate with a female and the winner gets to reproduce, passing on his victorious characteristics to his offspring
  • Has behavioural consequences - the characteristics that are passed on are those that allow males to outcompete their rivals, such as deceitfulness and aggression
  • This means males may benefit from being aggressive to acquire fertile females, protect them from harm, and win against competing males
• What is dimorphism?

  • A consequence of intra-sexual selection - males and females look very different due to different preferences
  • Size matters due to physical competition between males as larger males have an advantage, therefore more likely to have reproductive success
  • Female youthfulness is selected as males prefer to mate with more fertile women e.g. a large waist-to-hip ratio in women
• What is one strength of the evolutionary explanation?

  • Research support for intersexual selection: Clark & Hatfield (1989) sent male and female students on a university campus to approach others saying they found them attractive and asked them to go to bed with them the same night
  • 75% of males agreed, 0% of females
  • Shows females are much choosier than men when selecting sexual partners, evolving different strategies to ensure reproductive success - supports Trivers (1972)
• What is another strength of the evolutionary explanation?

  • Research support for intra-sexual selection: Buss (1989) surveyed 10k adults in 33 countries on attributes that the theory predicted to be important in partner preference
  • Found that females preferred resource-related, financial characteristics, and males value physical attractiveness and youth as signs of good reproductive capacity
  • Reflect consistent sex differences in partner preferences, supporting dimorphism in intra-sexual selection
• What is one limitation of the evolutionary explanation?

  • Cultural differences: Kasser and Sharma (1999) analysed 37 cultures and found that women value resource-related characteristics in mates MORE in cultures where the status and educational opportunities of women are limited
  • This weakens the evolutionary explanation as it underestimates the role of social and economic factors in establishing mate preference patterns, making research an example of ethnocentrism
• What is another limitation of the evolutionary explanation?

  • Not universal: female's preferences for high-status men may be dependent on context instead of being universal
  • Buller (2005) pointed out that majority of studies attempting to determines female mate preferences were carried out on female undergrads - their preference for high status men may just be a preference of men with similar interests or educational prospects to their own
  • Shows a correlational relationship, weakening evolutionary psychologists' claim that female preference for high status men is universal due to weak evidence