evolutionary explanations

• evolution is the process of adapting through natural selection
• human reproductive behaviour is the different mating strategies used by males and females.
• Socio-biological explanations are a theory of relationships based on biological determinants.
• Darwin 1871 proposed the concept of sexual selection which concerns the selection of characteristics aiding reproductive success.
• sexual selection is the survival of the most attractive. it is the ability to find a mate and reproduce effectively.
• natural and sexual selection are separate processes as the characteristics that facilitate reproduction do not necessarily increase survival chances. An example of this is male peacocks and their feathers.
• Intra-sexual selection is mate choice. members of one sex, usually males, compete with each other for females.
• inter-sexual selection is mate choice where there is a preference of one sex for members of the opposite sex who usually possess certain qualities.
• The winners of sexual selection get to mate and the losers genes are not passed on.
• Sexual dimorphism is the differences in appearance of males and females of the same species such as colour, shape and size. This suggests that males are competing for attention of females and in many species, females do the choosing of mates.
• Anisogamy is the differences between male and female sex cells. This leads to differences in the level of investment in reproduction
• Males produce 110 million sperm per ejaculation. Therefore their best strategy is to mate with many females because this should result in the maximum number of offspring. Men are fertile for a lot longer.
• Males are less certain of paternity and therefore engage in polygamy, where they mate with multiple females to enhance reproductive success.
• Females produce eggs, each of which contains a store of food for the growing embryo. Women have few relatively large eggs and are fertile for approximately 25 years.
• Females are certain of maternity and engage in monogamy, where they mate with only one mate.
• Trivers 1972 found evidence of intra-sexual selection. When females invest considerably more than males, men will compete among themselves to mate with females. Therefore, women will be more discriminating than men in their choice of sex partner because the consequences of mating with an unsuitable partner are greater. Inter-sexual selection
• Fisher 1930 developed the sexy sons hypothesis suggesting females select attractive males as they will produce sons with the same attractive features, increasing their sons' and own reproductive fitness.
• Men and women look for different things in a partner and adopt different mating strategies.
• Mens preferred strategy is intra-sexual selection - quantity over quality. The best strategy for males is to have as much sex with fertile women as possible.
• Womens preferred strategy is inter-sexual selection - quality over quantity. The best strategy for females is to carefully select their mate.
• Females are considered choosy. This requires time and energy and can impair survival but genetic quality of mate will determine half genetic quality of an offspring.
• In partners, females look for:

  • ability to invest resources in her and her children - Buss 1989
  • ability to protect her and her children
  • someone who shows promise as a good parent
  • sufficiently compatible to ensure minimal cost to her and her children - Buss 2003
• In partners, males look for:

  • Signs of fertility such as youth and physical attractiveness – Buss 1989
  • Good health
  • Child bearing hips
• Buss 1989 found support for preferences in relation to anisogamy. Buss surveyed 10,000 people in 33 different countries, asking ppts to rate 18 characteristics on how important they would be in choosing a mate. He found that females valued resource-related characteristics and males valued reproductive capacity and youth. This reflects sex differences in mating strategies as a result of anisogamy and supports predictions about partner preference based on sexual selection theory.
• Females engage in dating to find the best male who is willing to invest in them and their offspring.
• Clark and Hatfield 1989 found support for female choosiness. Male and female participants asked students on a university campus if they would sleep with them. 0% of female students agreed but 75% of males immediately agreed. This supports the evolutionary theory because it demonstrates how females are choosier than males when it comes to sexual partners and males have evolved with a different strategy to ensure reproductive success.
• Penton-Voak et al 1999 found evidence that female mate choice varies across menstrual cycle. Women typically choose feminine looking men for long-term relationships as it suggests kindness and cooperation. For short-term relationships during ovulation, the preferred appearance was masculine. This suggests genetic benefits in producing masculine offspring. However, Wood et al 2014 meta-analysis contradicts this research, specifically the claim of preferences for masculine males when females were most fertile.
• Evolutionary explanations cannot explain homosexual relationships. The basic principle of sexual selection is based on reproductive success and passing on genes to next generation, which is not a factor in homosexual relationships. Evolutionary explanations overemphasise reproduction as it assumes sexual attraction and behaviour is centred around reproduction. It cannot account for the behaviour of some of society as it ignores homosexual relationships and heterosexual couples who choose to remain childless.