1. evolutionary explanations

what is sexual selection

an evolutionary explanation of partner preference

• attributes or behaviour that increase reproductive success are passed on and may become exaggerated over succeeding generations of offspring

what is human reproductive behaviour

any behaviours which relate to opportunities to reproduce and thereby increase the survival chances of our genes

• includes evolutionary mechanisms that underly our partner preferences, such as mate choice and competition

anisogamy

anisogamy = differences between male and female sex cells (gametes) and is the basis of human reproductive behaviour

• male gametes (sperm) - small, highly mobile, created continuously in vast numbers, do not need much energy to be produced

• female gametes (eggs or ova) - relatively large, static, produced at intervals for a limited number of fertile years, require significant energy investment

a consequence of anisogamy

there is no shortage of fertile males but a fertile female is a much rarer ‘resource’

importance of anisogamy

it is important in partner preference as it gives rise to two types of sexual selection

1. inter-sexual selection

2. intra-sexual selection

inter-sexual selection

it is between the sexes

• the strategies that males use to select females, or females use to select male 

• it is the preferred strategy of the female, quality over quantity (ova are rarer than sperm)

female preference in inter-sexual selection

it determines which features are passed onto the offspring

• eg if height is considered an attractive male trait by females then it would increase in the male population over successive generations 

• because in each generation, females will select the tallest males 

• thus that characteristic gradually becomes exaggerated (a runaway process)

what did fisher develop

a sexy sons hypothesis - genes we see today are those that enhanced reproductive success

• a female who mates with a male who has a certain characteristic then will have sons who inherit this ‘sexy’ trait 

• her sons are also more likely to be selected by successive generations of females who will mate with her offspring

• thus the preference of this ‘sexy’ trait is perpetuated 

intra-sexual selection

it is within each sex

• such as the strategies between males to be the one that is selected 

• it is the preferred strategy of the male, quantity over quality (there is plentiful supply of sperm)

what do males compete for

to be selected to mate with a female

• winner reproduces 

• thus characteristics that contributed to his victory may be passed on to his offspring 

what has this strategy given rise to

dimorphism = males and females look very different due to intra-sexual selection

• larger males have an advantage and thus more likely to be reproductively successful - females do not compete for reproductive rights so there is no evolutionary drive towards favouring larger females 

• in females, youthfulness is selected as males have a preference to mate with younger more fertile women 

behavioural consequences of intra-sexual selection

these are controversial

• characteristics that are favoured and passed on are those that allow for a male to outcompete his rivals, including deceitfulness, intelligence and aggression

evaluation

1. research support for inter

2. research support for intra (& COUNTERPOINT)

3. social and cultural factors

4. homosexuality

research support for intra

• supporting evidence for male competition in mate selection 

• buss surveyed over 10000 adults in 33 countries and found men preferred youthful, attractive partners (indicators of fertility), while women preferred resource-rich, ambitious partners 

• preferences align with intra-sexual selection predictions - males competing for fertile females, females choosing resourceful mates 

research support for inter

• there is empirical support for the idea females are choosier than males 

• clark & hatfield approaches university students asking: would you go to bed with me tonight? with 75% of men agreeing and 0% women 

• demonstrates sex differences in short term mating strategies as women are more selective and consistent with inter-selection theory 

• supports evolutionary predictions that female choosiness evolved to ensure investment from males and avoid reproductive costs 

counterpoint

• sexual selection theory oversimplifies human mating behaviour 

• modern relationships often involve contraception and cultural expectations, which reduce biological pressures - means evolutionary explanations may not apply equally across all societies and time periods 

• suggests sexual selection may be less relevant in explaining contemporary human behaviour 

social and cultural factors 

• evolutionary theory ignores the impact of social and cultural change 

• study found gender role changes have reduced traditional sex differences in partner preferences - social norms, education and economic independence now influence choices more than reproductive fitness 

• suggests partner preferences are not purely evolutionary but shaped by cultural context

homosexuality

• sexual selection theory cannot fully explain non-heterosexual attraction 

• same sex relationships dont lead to reproduction but still involve emotional bonds and mate preferences - indicares other factors (eg social or emotional fulfilment) may influence attraction beyond reproductive advantage 

• challenges universality of evolutionary explanations and suggests human sexuality is more complex