evolutionary explanations

• key words

  • sexual selection - ability to find a mate and reproduce successfully
  • natural selection - ability to survive in a particular environment
  • genotype - all genes / genetic makeup
  • phenotype - observable characteristics / ones expresses, influenced by genetics and the environment
• evolution standpoint

  • humans adapt to environment overtime, as does their behaviour to help them
  • sociobiology - explains social behaviour in evolutionary terms
  • if a behaviour is adaptive it means it leads to increased survival and reproduction
  • means the gene that causes this behaviour will be passed onto the next generation
  • sociobiological explanations see attraction as an adaptive behaviour
• anisogamy

  • differences between male and female sex cells (gametes)
  • females (eggs) = few, large, energetically expensive (limited to 300)
  • males (sperm) = many, small, energetically cheap (single ejaculation can contain 40 - 600 million sperm)
  • female invests more so shes going to be more choosy with her choice of mate
  • females are limited to number of offspring, for men it is virtually unlimited
• types of sexual selection

  • intERsexual selection - the preference of one sex for the member of the opposite sex who has certain qualities, preferred female strategy, quality over quantity (making choice)
  • intRAsexual selection - competition between males to be able to mate with a female, the winner gets to pass characteristics that contributed to his victory onto the offspring (quantity over quality)
• intERsexual selection

  • the preference of one sex for the member of the opposite sex who has certain qualities, preferred female strategy, quality over quantity (making choice)
  • ova are rarer than sperm and are energetically expensive, women make a greater investment of time
  • choice of wrong partner is more serious for women, choosy because they stand to lose if they invest resources in substandard partners
  • so they look for partners that can offer resources (food, territory, protection) ensuring her child will have a greater chance of survival and also pass these genes on too
  • attractive traits will be increased in the population over successive generations (runway process)
  • sexy sons hypothesis - female mates with desirable male, son inherits these characteristics and increased likelihood son will then mate in the future
• intRAsexual selection

  • competition between males to be able to mate with a female, the winner gets to pass characteristics that contributed to his victory onto the offspring (quantity over quality)
  • dismorphism - larger males have advantage in competition and are more likely to mate, but females do not compete for reproductive rights so there is no evolutionary drive for favouring large females
  • the less time a man spends with a woman, the more chance they have to find someone else to empregnate, when men show decreased attraction after sex its an evolved strategy to ensure they dont spent too much time with 1 woman
  • women dont need to sleep around - they only need to find one man and can be more choosy
  • anisogamy says the males optimum reproductive strat is to mate with as many fertile females as possible
• behavioural consequences of competition for fertile mates

  • preference for youth and sensitivoty to indicators of youth (certain characteristics) as well as fertility (certain body shape)
  • reproductive value - probability of reproducing in the future
  • fertility - probability of reproducing now
  • youthfulness is an indicator of both reproductive value + fertility
  • can be signalled by things like smooth skin, good muscle tone, full lips, high energy levels, sprightly gait (symons)
  • female fertility is closely related to age, so men are attracted to younger, attractive women
  • but men are fertile their whole life so their fertility is less related to age and the preference for youth and attractiveness is more pronounced in men than women
• research support for preferences related to anisogamy

  • buss explored what people look for in a marriage partner, using over 10,000 people from 37 different cultures and a wide diversity of religious, political and economic groups
  • askes questions relating to age and attributes that are predicted to be important in partner preference
  • findings...
  • females looking in males for ... resource related things (finance, ambition)
  • males looking in females for ... signs of good reproductive capacity (curvy, youth, attractiveness)
  • supports sexual selection theory
• research support for inter-sexual selection

  • clark and hatfield investigates differences in reproductive behaviour between men and women
  • attractive male and female experimenters approached strangers on uni campus and asked them ... would you go on a date with me? would you go back to my apartment? would you have sex with me?
  • 0% of women said yes to the sex, compared to 75% of men who did
  • shows men have a psychological mechanism to ensure success in short term mating, looking for...

  1. desire for sexual variety
  2. tendency to let little time elapse before seeking sex
  3. willingness to consent to having sex with strangers
• evolutionary idea of sexual selection CRITICISM

  • ignores social and cultural influences
  • partner preferences have been influences by fast changing social norms of sexual behaviour (they develop faster than evolutionary timescales)
  • come about due to cultural factors like contraception availabilty
  • womens greater role in the workplace means theyre no longer dependent on men to provide for them
  • bereczkei - argues social change has consequences for womens mate preference, which may no longer be resource orientated
  • chang - compared partner preferences in china over 25 yrs and found some had changed but others stayed the same, corresponding with the social changes at the time
  • mate preferences are therefore a combination of evolutionary and cultural influences
• support from lonely hearts research

  • wayneforth and dunbar - studied lonely hearts ads in newspapers, opportunities for men and women to describe the qualities they desired in a potential partner, while saying what they had to offer
  • found women tended to offer physical attractiveness and indicators of youth (sexy, curvy, flirty)
  • men offered resources more than women (successful, fit, ambitious) and sought youth and attactiveness
  • supports preferences related to anisogamy
• support from waist hip ratio research

  • evolutionary theory makes predictions about partner preference that can be tested empirically, one being men show preference for the female body shape that signals fertility
  • singh - what matters to men is not the body size, but the ratio of waist to hip sizes
  • they generally find any hip - waist size attractive so long as the ratio of one to another is about 0.7
  • combination of wider hips and narror waist is attractive because it is an 'honest signal' (hard to fake) that a woman is fertile but not currently pregnant