Evolutionary explanations

• AO1 - Evolution

  Each living thing (organism) has a set of characteristics encoded by its genes.

  The organism inherits its genes from its parent(s).

  Variations between organisms are caused by variations in the genotype.
• AO1 - Evolution

  Characteristics evolve because they have been passed from one generation to the next via the genes.

  This requires the organism:

  • To live to reproductive age.
  • To mate successfully.
  • To ensure the offspring’s survival.
• A01-Natural & Sexual Selection

  • Natural selection
  • Ability to survive in a particular environment (fitness).
  • Sexual selection
  • Ability to attract/find a mate and reproduce successfully.

  These are separate processes. 

  The characteristics that facilitate reproduction do not necessarily increase survival chances.
• A01-Sexual selection

  • Male cells (sperm) are small, mobile and continuously produced from puberty to old age
  • Female cells (ova) are larger static and produced at intervals for a limited numbers of years

  = this is anisogamy

  Consequences of anisogamy are that there are plenty of fertile males but fewer females.

  This gives rise to different mating strategies.
• Intra-Sexual Selection

  Usually males compete with each other for ‘access’ to members of the opposite sex – victors mate and pass on their genes – winning traits are passed on to the next generation.

  What is the impact on mating behaviour?

  Mate competition

  Competition necessary as females are a limited resource and are choosy.
• Intra-Sexual Selection

  Intra-sexual selection pressures lead to certain patterns of human reproduction behaviour:

  Male aggression - the most aggressive male is more likely to reproduce

  Male preference for youthful and fertile women. Why? 

  They are signs of fertility leading to reproductive success.
• Inter-Sexual Selection

  Female strategy – quality over quantity!

  Females make a greater investment of time, commitment and other resources before, during and after birth. They need to be choosier than males to seek a male who will provide healthy offspring and support them with resources.
• Inter-Sexual Selection

  Impact on mating behaviour:

  Preferences of both sexes determine attributes that are passed on- e.g. if height is a genuine marker of fitness in males, the females who choose the tallest mates will have greater reproductive success and innate preference are passed on.

  Over time, this leads to taller and taller men being selected (runaway process).
• The Research Evidence: What Men & Women want:

  Franzoi & Herzog (1987)

  Men were predominantly concerned with weight

  Women like men with a firm bum and large chest
• The Research Evidence: What Men & Women want:

  Singh (1993, 2002)

  • Men like women with a low waist to hip ratio.
  • Findings were that any hips and waist size can be attractive as long as the ratio of one to the other is 0.7 (thought to signify that the female is fertile but not currently pregnant)

  = This shows that evolutionary factors are reflected in patterns of human reproductive behaviour through partner preferences.
• (+) support for the relationship with intra-sexual selection

  Aim: what each sex seeks in long-term partner.

  Conducted large cross-cultural study into human mating preferences.

  > 10,000 people, 37 cultures.

  Rated 18 characteristics on importance when choosing mate. Rating scale ran from 3 (indispensable) to 0 (irrelevant).

  Found consistent gender differences.
• (-) Relationships ignores social and cultural influences

  Partner preferences have impacted over time by changing social norms and cultural practices. These have occurred too rapidly to be explained in evolutionary terms.

  Chang et al (2011) – some preferences have changed and others have remained the same over 25 years in China.

  = this suggests that both evolutionary and cultural influences must be taken into account when explaining human reproductive behaviour.
• (+) Mate choice in real life

  Many of the studies carried out in this area have been restricted to expressed mate preferences rather than real –life  mate choice.

  However,

  A study of actual marriage (Buss) confirmed that men do indeed choose younger women.

  Statistics also show that men who divorce and remarry tend to choose women who are increasingly younger than they are.