sexual selection and humn reproductive behaviour

• Sexual selection:

  • Charles Darwin’s theory of sexual selection suggests that there are some characteristics that have evolved because they provide a reproductive advantage (allowing the individual to pass on their genes)
  • These characteristics provide an advantage in human reproductive behaviour because they are either attractive to potential mates or they provide an advantage over competitors for reproductive rights 
• Sexual Selection:

  • Sexual selection is therefore different to natural selection, because in natural selection it is characteristics that provide a survival advantage that have evolved, whereas sexual selection is about characteristics that provide a reproductive advantage which evolve 
• Anisogamy:

  • This refers to the difference between male and female sex cells (gametes)
  • Male gametes (sperm) are created continuously in vast numbers and do not require much energy to produce
  • Female gametes (eggs) are produced at intervals for a limited time during the fertile years and require a huge amount of energy
  • This means that there is no shortage of fertile males but a fertile woman is a rare ‘resource’
• Ansigonamy:

  • Therefore, males’ best strategy is to compete with each other to mate with many females, because this should result in the maximum number of offspring (Intra-sexual selection)
  • However, 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)
• Inter-selection selection (female):

  • This is when members of one sex (usually female) evolve preferences for desirable qualities in potential mates.
  • This is the preferred strategy of the female – quality over quantity – because they invest more time, commitment and resources before, during and after birth
  • The egg cell is also only produced in intervals for a limited time only 
• Inter-selection

  • Therefore, the best mating strategy for females is to be choosy and select a genetically fit partner who is able and willing to provide resources
  • This female preference for a genetically fit male determines which features are passed on to their offspring
  • For example, if height is considered an attractive trait then, over successive generations, females would mate with tall males and produce taller sons
• Inter-selection:

  • As a result, there would be more taller males in the population and males will have to compete for a female based on the desirable traits chosen by women (e.g. How tall they are)
  • The preference of one sex, therefore, determines the areas in which the other sex must compete
• Intra-Sexual Selection (Usually Male)

  • In intra-sexual selection, individuals of one sex (usually males) must outcompete other members of their sex in order to gain access to members of the other sex
  • Successful individuals are able to mate and so pass on their genes
  • Whatever characteristic that leads to success in these same-sex contests (e.g. Aggression, size and strength, etc.) is passed down to offspring and becomes more widespread in the gene pool 
• Intra-selection

  • Males’ best strategy to pass on their genes is to mate with as many fertile women as possible
  • This means that men compete for fertile women, meaning they have an evolutionary preference for those who show features of fertility (e.g. Young, certain body shape/facial features) 
• AO3:

  • Research to supprt evolutionary explanations for partner preference
  • Buss (1989) found that females placed greater value on resource-related characteristics in males (e.g. Financial prospects, ambition, etc.) than men did 
  • Males were more interested in looks, chastity and youthfulness in females
  • The study supports the findings that men seek fertile females to pass on genes, while women are more selective in choosing mates due to their wealth and resources.
• AO3:

  • esearch support for inter-sexual selection.
  • Clark and Hatfield (1989) shows that females choosiness is a reality of heterosexual relationships in their study on university students
  • They found that 75% of males would agree to ‘go to bed with’ a female student who approached them with the request, whereas not a single woman agreed to the request when a male approached them.
  • The evolutionary theory suggests that females have evolved to be more selective in selecting sexual partners due to the potential loss of choosing an unsuitable male.
• AO3:

  • limitation of human reproductive behaviour is that they ignore social and cultural influences
  • For example, the availability of contraception is a cultural change that now means females do not have to be choosy when selecting a sexual partner.
  • Also, many women work now, meaning they do not depend on males for resources so they do not need to pick a sexual partner based on the resources he can provide for her and her offspring
  • Therefore, mate preferences may be influenced by both evolutionary and social/cultural factors, and it's incorrect to assume that only one plays a role.
• AO3:

  • Support for sexual selection comes from a study of lonely hearts advertisements in American newspapers
  • In the adverts, Waynforth and Dunbar (1995) found that men offered qualities related to resources such as ‘successful, fit, ambitious’
  • However, women offered qualities linked to physical attractiveness such as ‘flirty, exciting, curvy, sexy’
  • This supports the idea that females have evolved to prefer males who are genetically fit and can provide resources for them and their offspring, whereas males have evolved to look for fertile women so they can pass on more of their genes
• AO3:

  • There is research to support the evolutionary explanation that males prefer a female body shape that signals fertility
  • Singh (2002) studied this in terms of the ratio of waist to hip sizes. Males generally prefer any hip-waist ratio attractive as long as the ratio of one to the other is about 0.7
  • This hip-waist ratio indicates that the woman is fertile but not currently pregnant, supporting the evolutionary idea that males have evolved to seek fertile women to pass on as many of their genes as possible