Evolutionary Explanations

• natural selection


  ability to survive in a particular environment.

  survival of the fittest
• sexual selection


  key explanation of Darwin's theory explaining how evolution is driven by competition for mates and development of behaviours or characteristics that ensure reproductive success.

  the ability to find a mate and reproduce successfully - survival of the sexiest

  characteristics may be advantageous, such as males who behave aggressively and females with characteristic traits of fertility
• anisogamy


  differences between male and female sex cells (gametes)
• evolutionary explanation


  explains human behaviour - adaptiveness and reproductive success

  partner selection - genetically inherited by one generation to another, then must have a specific value for human species.
• sperm cell


  highly mobile

  extremely small

  created continuously in large numbers over years

  doesn't require a lots of energy to produce
• egg cell


  relatively large

  doesn't move around much

  produced at intervals for a limited number of years

  requires a lot of energy
• Inter-sexual selection


  preferred strategy of women

  'quality over quantity' approach and is favoured by females as they place a greater investment of time, energy and resources in raising a child compared to males

  females need to be sure that their partner will provide the right genetic fit, by being willing to and able to provide necessary resources to support them and their child
• Fisher's 'sexy son hypothesis'

  suggests that a female who mates with a male who has a certain characteristic e.g. height then will have sons who inherit this 'sexy' trait.

  her sons will be more likely to be selected by successive generations of females who will mate with her offspring.

  ensures that female's genes are passed on through several generations increasing the likelihood that these genes will remain in the gene pool
• Intra-sexual selection


  preferred male strategy

  'quantity over quality' approach and is favoured by males as their optimal mating strategy is to mate with as many fertile female partners as possible

  explains the differences in body size and physical appearance between males and females, physical dimorphism
• Strength - Supporting Research related to Anisogamy

  Buss conducted a survey of over 10,000 adults in 33 countries.

  - asked questions relating to age and variety of attributes that evolutionary theory predicts should be important in partner preference.

  results:

  female mating preferences: placed greater value on resource - related characteristics e.g. financial prospects, ambition and industriousness.

  male mating preferences: placed more importance on good looks and chastity and preferred younger mates.

  
  

  findings reflect sex differences in mate strategies due to anisogamy. supporting predictions about partner preferences obtained from sexual selection.

  can be applied across different cultures.
• Strength - Supporting Research for Inter-sexual Selection

  Clark and Hatfield showed females are more selective when it comes to potential mates.

  Would you go on a date with me? males: 50%, females: 50%

  Would you go back to my apartment? males: 60% females: 6%

  Would you have sex with me? males: 75% females: 0%

  supports the idea men have an evolutionary pre-disposition to want to impregnate as many women as possible
• Strength - Support for Partner Preferences from waist-hip ratio

  makes several predictions about partner preference that can be tested empirically.

  Singh studied this in terms of waist-hip ratio.

  males generally find any hip and waist sizes attractive as long as ratio of one to the other is around 0.7

  combination of narrow waist and wider hips is attractive as it's an 'honest' signal that women is fertile but not currently pregnant.

  shows that evolutionary factors are reflected in patterns of human reproductive behaviour through partner preferences.
• Weakness - Partner preferences ignore social and cultural differences

  partner preferences over past century have been influenced by changing social norms

  these develop faster than evolutionary timescales and instead come due to cultural factors such as availability of contraception.

  Bereczkei argues this social change has consequences for women's mate preference, which may no longer be resource orientated.

  Chang compared partner preferences in China over 25yrs and found some had changed bit others stayed the same, corresponding with social changes at the time.

  
  

  suggests that some evolutionary explanations for inter-sexual selection no longer apply in modern climate

  therefore the income of a combination of evolutionary and cultural influences. any theory that fails to account for both is a limited explanation.