Evolutionary theory

• What is sexual selection?

  It refers to Darwin's suggestion that traits could evolve because they were attractive to members of the opposite sex
• What is intersexual selection?

  This refers to the effects of choice on members of the opposite sex
• What is intrasexual selection?

  It refers to competition between members of the same sex for access to mates
• Basis of intersexual selection and human reproductive behaviour?

  • Evolutionary theory argues that behaviours including mate choice occur to maximise the chance of passing on genes.
  • This predicts a difference in mate choice between men and women as they faced different evolutionary pressures in the EEA (environment of evolutionary adaptation), and evolved distinct strategies for survival success. 
  • Differences between the biology of sexes means they have different strategies for reproductive success.
  • This includes differences in gametes, known as anisogamy.
• What makes females' limited reproductive rate?

  • They produce only a few large energy-rich eggs and are only fertile for 72 hours a month from puberty to menopause.
  • Pregnancy and lactation (breast feeding) and a large investment of energy into each offspring. 
  • Maximum of 1 offspring per 2 years. The exact number of offspring is limited by access to resources that are needed for survival
• What makes males' high reproductive rate?

  • Large numbers of sperm are produced and males are fertile every day from puberty to death. 
  • There is little energy required - only that it is required for sperm production and mating 
  • Limited by access to fertile females

  Because of these differences in biology, evolutionary theory makes predictions about behaviour and preferred characteristics.
• Preferred characteristics of females?

  • Females prefer males with resources to provide for them - also characteristics that may indicate resources such as ambition and intelligence.
  • They then prefer older males as they may have had more time for resources. 
  • Females are much more decisive in picking a partner as their investment and cost is much higher than a male.
• Preferred characteristics of men?

  • Males prefer indicators of fertility. They prefer a thin waist, large bottom and being young. 
  • Being young indicates more general fertility.
  • Thin waist indicates an absence of pregnancy and a large bottom means bigger fat reserves for the child in times of food scarcity.
  • Symmetrical faces also indicate good genes and free from illness
  • Men are more promiscuous as they do not have a large cost of choosing a bad choice of female.
• Positive evaluation regarding majority for evolutionary theory?

  • Buss(1989) - A study done on 9000 adults over 37 cultures in Europe, South and North America and Africa regarding important characteristics w/ a questionnaire. They found:
  • Men value chastity more than the women (sexual abstinence = it is their child and not anyone else’s)
  • Men value physical attributes more (34/37 cultures) 
  • Women value earning potential more (36/37 cultures) 
  • Men prefer women younger than themselves and women viceversa.

  It supports the evolutionary theory and in agreement with evolutionary predictions.
• Positive evaluation of Buss' study?

  • Buss studied 37 cultures and found significant similarities between mate choices.
  • This suggests that it is much more of a genetic cause than cultural basis.
  • It is rather nurture than nature in determining mate choice.
• Negative evaluation of Buss' study?

  • However, it did not distinguish between long term marriage partners and a one night stand.
  • Kenrick asked students to rank attribute according to the four levels of intimacy.
  • According to this, if it is marriage based, both sexes prefer their partner to have good intelligence but if on a one night stand, it matters less to the men.
  • The findings go against the evolutionary theory and also suggests that the theory is alpha gender biased suggesting that only females prefer intelligence. 
• Supporting study for the evolutionary theory? (procedure)

  • Clarke + Hatfield (1989) - men and women experimenters on a college campus and all said “Hi, I’ve been noticing you around campus and I find you very attractive”

  3 levels of questions:

  1. Will you go on a date with me?
  2. Would you go back to my apartment with me?
  3. Will you have sex with me?

  The experimenters recorded percentage of agreeing and verbal comments. 
• Supporting study for the evolutionary theory? (findings)

  • Females:
  • 50% agreed to go on a date, 6% agreed to go back to his apartment and 0% agreed to have sex. The women found it insulting and some found it bizarre
  • Males:
  • 50% agreed on a date, 69% agreed to go back to her apartment and 75% agreed to go to have sex. Males who declined said they had a prior commitment to the parents of a fiance.
  • This shows females are choosier.
• Reductionist evaluation of the evolutionary theory?

  • Reductionist - Complex social behaviour is reduced to reproductive strategy.
  • The meaning of life is simplified to understanding genes. It ignores other factors like the role of culture.
  • Men value physical characteristics more as the media may emphasise the importance of attractive characteristics.
  • It does not consider individual differences such as in homosexual ones where there is no reproductive success.
  • The theory is limited.
• Deterministic evaluation of the evolutionary theory?

  • Our biology determines our mate choice.
  • We have no little to no choice in how we pick our partners as it is based on genetics.
  • Some people say  they put a lot of thought and deliberation into picking a mate.
  • It is also socially sensitive as men may use it as an excuse for being unfaithful and it also reinforces negative stereotypes for women being “gold diggers”.
  • Therefore, the evolutionary theory is both socially sensitive and promotes stereotypes.
• What is intrasexual selection?

  • Competition does not end with just mating. In chimpanzees, many males may mate with a female.
  • There are then several sperm in her reproductive tract.
  • Chimpanzees have then evolved to have an increase of sperm so they can compete with rival sperm. This is called sperm competition. 
• Supporting real life examples of intra-sexual selection?

  • Testes size indicates the degree of sperm competition. The larger the more competition.
  • Testes of humans are larger than gorillas in size but smaller than chimpanzees who mate with other male chimpanzees.
  • This supports the evolutionary theory as this shows that there has been intra-sexual selection resulting in bigger testes.
  • This suggests females are being more promiscuous.