Psychology Unit 3 - Relationships - Evolutionary explanations of human reproductive behaviour

• animals are grouped into species - within species is variation; not everyone/thing is identical. 
• part of variation is due to differences caused by genetic makeup
• genes are 50% from each parent.. sometimes genes can mutate
• mutations are most likely harmful and when individual reproduces likely to pass mutation on
• mutations can however be beneficial
• survival may be benefited by a mutation by helping them to adapt to their environment
• those who are adapted to their environment stand more chance of surviving into adulthood and reproducing offspring with mutated gene
• over a long period if the characteristic caused by the mutation is suffietient it will become a permenant feature of the particular group of animals
• evolution is the process of natural selection by which new species arise from gradual changes to the genetic makeup of existing species over long periods of time
• Darwin's theory of evolution by natural selection is portrayed as the 'survival of the fittest'
• Darwin's theory is innaccurate
• Fitness isnt a quality of an individual, like strength or speed, but refers to the capacity to reproduce
• Therefore fitness means reproductive fitness

• uses Darwinian concepts to generate testable hypotheses about human behaviour based on assumption the individuals act in ways increasing survival of their genes

• According to Miller (1998) the application of sexual selection theory to human behaviour is evolutionary psychology's greatest contribution to understanding human behaviour.

• Sexual dimorphism concerns the different characteristics the males and females possess
• evolution explains sexual dimorphism as developing through the process of natural selection because the evolution of different features bestowed an adaptive advantage.
• adaptive advantage = increased the chances of survival into adult hood and sexual maturity, where genes are passed to the next generation.
• sexual selection involves the selection of characteristics increasing reproductive sucess.  for example a peacocks tail.
• reproductive success involves the production of healthy offspring, surving to sexual maturity and reproducing themselves
• differences between male and female sexual behaviour arise; this is because they are subject to different selective pressures.
• the differences occur due to anisogamy, differences between the nature and amount of gametes produced
• Males lots of sperm etc...
• Females limited eggs etc... 
• natural selection therfore favours femal behaviours maximising the chances of successfulreproduction through various strategies, like careful mate selection, monogamy and high parental innvestment
• females choose from males that are available 

Body symmetry and waist to hip ratio

• body symmetry and waist to hip ratio are indicators of genetic fitness 
• form universal characteristics of attractiveness
• indivduals with body symmetry and a certain waist to hip ratio are seen as attractive
• they have enhanced chances of reproduction and are percieved as having greater reproductive fitness
• facial symmetry is the best predictor of body symmetry and this is seen as attractive
• males and females with near perfect body symmetry report two to three times as many sexual partners as those with the most asymmetrical bodies
• Moller (1992) explained females choosing males with symmetrical features in terms of the handicap hypothesis. Symmetry requires genetic precision and only good genetic quality males can produce it
• Waist to hip ratio is another universally attractive physical characteristicconveying info about female fertility
• larger waist to hip ratio associated with better health status and greater reproductive ability

Physical Attractiveness

• males use physical attractiveness to indicate reproductive fitness more than females
• men give a universally higher priority to good looks in females 
• females give a higher priority to resource provision in males
• this is because men value female partners in terms of fecundity, the ability to produce and care for children, and meny rely on womens physical attractiveness to estimate age and health, with younger, healthier women percieved as having greater reproductive fitness
• preference for largeeyes and lips etc.. is related to estimating a womens age and hence reproductive ability
• womens reproductive success is less dependent on finding fertile males for whom age is a less reliable indicator of fertility
• male fertility cant be assessed as accurately from physical apperance
• womens mate selection depends on their need for a provider during pregnancy and child rearing
• men seen as powerful, controlling resources that contribute to the mothers and childs welfare are more attractive
• although physical attractiveness is less important females are choosier in selecting mates as their investment is higher

Male Strategies

• Several male strategieshave evolved seeking to maximise opportunities and potential for mating success including:
• Courtship rituals - allow males to compete and display genetic potential through certain characteristics and resource abilities.  Miller (1997) sees evolution as shaping human culture e.g. language, music and humour to act as courtship displays to attract a partner.
• Size - males have evolved to be bigger; this demostrates strength for success in competition against other males.  Weaponry has evolves in some species for the same reason e.g. deer.
• Sperm competition - natural selection occured and acted upon males making them more competitive by producting larger testicles, more copious ejaculations and faster swimming sperm.
• Jealousy - males fear being cuckolded and spending resources raising another males child. Buss (1993) argues that men are fearful of partners being sexually unfaithful, whilst females fear emotional unfaithfulness, illustrating the male fear of cuckoldry and the female fear of partners spending resources on other females.
• Extra pair copulation - males mate with females other than their partners if given the opportuniuty.  Women gain from this, as having different fathers brings a wider genetic diversity to their children, increasing survival chances.

Female Strategies

• several female strategies have evolved to maximise opportunities and potential for mating success including:
• **** sons hypothesis - females select attractive males who will produce sons with the same attractive features, increasing reproductive fitness.  Attractive characterisitcs have an intitial adaptive advantage, but natural selection favours their enhancement, until they run away becoming bizarre.
• Handicap hypothesis - Zahavi (1975) believes that females select males with handicaps because it advertises ability to thrive despite handicaps; this demostrates superior genetic quality.  May explain why females finding males attractive who drink or take drugs in large amounts, as they are demonstrating an ability to handle toxins, a sign of genetic fitness.
• Courtship - this is used by females as a means of selecting males on the basis of reproductive fitness, through males demonstating strength, health and ability to provide resources.  Prolonged courtship rituals also benefit females; they make males invest time effort and resources incresing the chances of them not deserting.  Occurs through the human practice of datingwith males presenting gifts to females.

Cartwright (2000) 

FOUND - women with symmetrical breasts are more fertile than more asymmestrically breasted women

SUPPORTS the idea that body symmetry indicates reproductive fitness

Singh (1993)

used data from 50 years of beauty contest winners and ******* centrefolds to assess waist to hip ratiosof attractive women.

FOUND - small waist set against full hips was a consistent feature of female attractiveness while breast size, overall body weight and physique varied over the years.

SUGGESTS that waist to hip ratio is an indicator of reproductive ability.

Clark and Hatfield (1989) 

FOUND - males are more promiscuous 

SUPPORTING the idea of gender based differences in sexual selection

Boone (1986) 

FOUND - females prefer older males with access to resources while Kenrick and Keefe (1992) found that males prefer younger females ... 

SUPPORTING the theory

STRENGTHS

• Females often use deception to alter their appearance and lie about their age in order to appear younger and more fertile.  Males use deceit to exaggerate their resource provision capabilities and feign younger love in order to induce females to mate with them.  SUPPORTS the idea that males and females use different strategies to maximise reproductive potential.

WEAKNESSES

• Younger males often desire substantially older women; this goes against the evolutionary theory but it may occur due to wanting to mate with females proven to be fertile.
• Cross cultural replications havent supported the claim that there is a universal preference for a low waist to hip ratio
• Evidence suggests women dont need males like they used to