evolutionary explanations for partner preferences Flashcards
describe the evolutionary explanation for sexual selection (darwin 1871)
- characteristics that aid successful reproduction, rather than survival, are selected
- some physical characteristics are a sign of genetic fitness
- selected characteristics may become exaggerated over succeeding generations of offspring
what is anisogamy?
differences between male and female sex cells (gametes)
describe male gametes (sperm)
- small
- highly mobile
- created continuously in vast numbers from puberty to old age
- do not need much energy to be produced
describe female gametes (eggs / ova)
- relatively large
- static
- produced at intervals for a limited number of fertile years
- require a significant investment of energy
what are 2 consequences of anisogamy?
- no shortage of fertile males but fertile females are rarer
- gives rise to 2 types of sexual selection
what are 2 types of sexual selection?
- inter-sexual selection
- intra-sexual selection
what is the preferred strategy of sexual selection for each sex?
- female = inter-sexual selection (quality > quantity)
- male = intra-sexual selection (quantity > quality)
what is inter-sexual selection?
- selection between sexes
- strategies male use to select females or females use to select males
inter-sexual selection: trivers (1972)
- female makes a greater investment of time, commitment and other resources before, during and after the birth of her offspring
- consequences of making a wrong partner choice are more serious for the female so she needs to be especially selective
- female’s optimum mating strategy is to select a genetically fit partner who is able to provide resources
inter-sexual selection: runaway process
- female preference determine which features are passed on to offpsiring
- selected characteristic gradually becomes exaggerated
inter-sexual selection: sexy sons hypothesis (fisher 1930)
- genes we see today are those enhanced by reproductive success
- female who mates with a male who has a certain characteristic will have sons who inherit this ‘sexy’ trait
- her sons are also more likely to be selected by successive generations of female who will mate with her offspring
- preference for this ‘sexy’ trait is perpetuated
what is intra-sexual selection?
- selection within each sex
- strategies between on sex to be the one selected
intra-sexual selection: competition
- competition between males to be selected to mate with a female
- winner of competition reproduces
- characteristics that contributed to his victory passed on to his offspring
- losing characteristics are not passed as they don’t mate
intra-sexual selection: dimorphism (males)
- in any physical competition between males, size matters
- larger males have an advantage so are more likely to be reproductively successful
- males and females end up looking very different
intra-sexual selection: dimorphism (females)
- don’t compete for reproductive rights so no evolutionary drive towards favouring larger females
- female youthfulness is selected as males have a preference to mate with younger, more fertile women
intra-sexual selection: behavioural characteristics
- controversial
- deceitfulness, intelligence and aggression allow a male to outcompete his rivals
- males may benefit from behaving aggressively to acquire fertile females and protect them from competing males
- leads to selection of aggressiveness in males
evaluation: research support for inter-sexual selection (clark and hatfield 1989)
- sent male and female psychology students across a university campus
- approached other students individually with the question ‘i have been noticing you around campus. i find you to be very attractive. would you go to bed with me tonight?’
- no female students agreed to the request; 75% of males did, immediately
- supports view that females are choosier than males when selecting sexual partners and that males have evolved a different strategy to ensure reproductive success
evaluation: reductionist to argue that one strategy is adapative for all males and another is adaptive for all females (buss and schmitt 2016)
- both males and females adopt similar mating strategies when seeking long-term relationships
- both sexes are very choosy and look for partners who are loving, loyal and kind
- more complex and nuanced view of how evolutionary pressures influence partner preferences which takes into account context of reproductive behaviour
evaluation: research support for intra-sexual selection (buss 1989)
- surveyed >10,000 adults in 33 countries
- asked questions relating to a variety of attributes that evolutionary theory predicts are important in partner preferences
- females placed greater value on resource-related characteristics than males did (eg. good financial prospects, ambition)
- males valued physical attractiveness and youth as signs of good reproductive capacity more than females did
evaluation: social and cultural influences underestimated
- partner preferneces over the past century have been influenced by rapidly changing social norms of behaviour
- these develop much faster than evolutionary timescales and come about due to cultural factors (eg. availability of contraception)
- women’s greater role in the workplace means they are no longer dependent on men to provide for them
- any theory that fails to account for the fact that partner preferences today are likely to be the outcome of a combination of evolutionary and cultural influences is a limited explanation
evaluation: social and cultural inlfuences (bereczkei et al. 1997)
social change has consequences for women’s mate preferences, which may no longer be resource-oriented
evaluation: cannot explain parter preferences of gay men and lesbian women
in homosexual relationships, partners are not assessing genetic fitness
evaluation: sexual selection and homosexuality (lawson et al. 2014)
- looked at ‘personal ads’ placed by heterosexual and homosexual men and women describing what they are looking for in a partner and what they are offering
- preferences of homosexual men and women differ just as they do in heterosexual men and women
- men emphasised physical attractiveness, women emphasised resources
- all people, regardless of sexuality, assess genetically-related qualities relevant to raising offspring (eg. kindness, protectiveness)
nature-nurture: eagley et al. (2013)
sexual partner preference is influenced by a combination of biological mechanisms, epigenetic mechanisms, as well as environmental factors such as differential interactions with parents and conspecifics
