Sexual selection and human reproductive behaviour

• Sex cells, mating
• Quality
  • Partner preference (+)
• Quantity
  • Students (+)
• Culture (-)
• Waist-hip (+)

Anisogamy

• Differences between male and female sex cells (gametes).
• Sperm are produced in large quantities, are very mobile and last for a short amount of time.
• Ova are produced much less frequently in smaller quantities and are less mobile but last for a longer period of time.
• No shortage of fertile males but a fertile female is a 'rare' resource
• Gives rise to two different mating strategies: inter-sexual selection (females) and intra-sexual selection (males).

Research support for preference related to anisogamy-

P- A strength of the sexual selection explanation is that there is research support for preference related to anisogamy.

E- Buss (1989) carried out a survey of over 10,000 adults in 33 countries which contained questions relating to attributes that the evolutionary theory predicts to be important in partner preference. He found that female respondents placed greater value on resource-related characteristics while males valued reproducive capacity (e.g. good looks and capacity) and preferred younger mates.

C- However, this could be an example of alpha bias in psychological research and therefore research such a this must be interpreted carefully to ensure that large generalisations are made.

E- Despite this, this findings reflect sex differences in mate strategies due to anisogamy. They support theories of sexual selection and can be applied across a number of cultures, reflecting fundamental human preferences.

Inter-sexual selection

• Preferred strategy for females.
• Females make a greater investment of time, commitment and energy (Trivers, 1972).
• Strategy is to select a genetically fit partner who is willing and able to provide resources.
• Female preference determines offspring characteristics.
  • E.g. Height being considered an attractive trait means that females will produce tall sons and daughters that have a preference for height. (Runaway process)
• '**** sons' hypothesis
  • A female mates with a male who has a desirable characteristic and this '****' trait will be inherited by her son. This increases the likelihood that successive generations of females will mate with her offspring.

Intra-sexual selection-

• Preferred strategy of the male.
• Competition between males to mate with a large quantity of females (rather than quality).
• Winner is able to pass of characteristics that contributed to victory.
• Benefit from behaving aggressively and thinking in certain ways.
• Optimum strategy is to mate with as many fertile females as possible.
• Relatively little energy and lack of post-coital responsibility.
• Preference for youth and indicators of youth as well as fertility.

Research support for inter-sexual selection-

P- Another strength is that there is research support for inter-sexual selection.

E- Clark and Hatfield (1989) showed that female choosiness is a reality of heterosexual relationships. Male and female psychology students were sent out across a university campus. They approached other students individually with the question: "I have been noticing you around campuss. I find you very attractive. Would you go to bed with me tonight?". Not a single female student agreed to the request while 75% of males did.

C- However, the responses of participants may have been influenced by social desirability bias as the males approached may not have wanted to be considered less masculine by rejecting sexual advances and the females may not have wanted to be seen as 'sluts' by immediately accepting sex from a stranger.

E- Nevertheless, the findings support evolutionary theory because, even if social desirability is a factor, it could be argued that labels being avoided stem from developed evolutionary behaviours. This is therefore a strength.

Ignores social and cultural differences-

P- However, a limitation of the sexual selection explanation is that it ignores social and cultural differences.

E- Partner preferences have been influenced by rapidly changing social norms of sexual behaviour which develop much faster than evolutionary time scales imply and have occured due to cultural factors such as availability of contraception. Womens' increasing role in the workplace means that they are no longer dependent on men to provide for them. Bereczkei et al. (1997) argue that social change may mean that womens' sex preferences are no longer resource-oriented. Other psychologists such as Chang et al. compared partner preferences in China over 25 years and found that some had changed but others remained the same, corresponding with the huge social changes at that time.

C- However, it could be argued that, despite differences in partner preference between cultures, the fundamental basis for human sexual behaviour remains the same on an evolutionary level.

E- On the other hand, this still undermines the evolutionary explanation as it suggests that even 'original' sexual preferences and behaviour could be culturally influenced.

Evaluation extra

Support from waist-hip ratio research-

P- Another stregnth is that there is support from waist-hip ratio research.

E- Singh (1993, 2002) found that what matters for males is not female body size but the ratios of waist and hip sizes. Up to a point, males find any of hip or waist size attractive as long as the ratio is about 0.7.

E- The combination of wider hips and narrower waist is attractive because this is an 'honest signal' that a woman is fertile but not currently pregnant.

L- This is a strength because is supports the idea that males will show a preference for a female body shape that signals fertility.