Relationships

Behaviours and bodily features that enabled our ancestors to reproduce would be passed onto their offspring who would inherit the feature of behaviour.

Intra-sexual selection (mate competition): members of one sex (usually males) compete with each other for access to members of the opposite sex. Males who were large, aggressive and able to beat rivals in fights would get to mate more often and have more offspring.

Inter-sexual selection (mate choice): members of one sex (usually females) choose which males to mate with. Females may prefer to mate with male with more resources.

Biology has programmed men and women to adopt different reproductive behaviours. Men generally seek younger women (as this is an indication of their fertility) and will mate with as many women as possible. Whereas women will generally seek faithful and committed mates who will stick around, powerful mates who can protect the family, and generally older men as they are more likely to be able to provide resources. Women are less likely to be promiscuous.

Men are more likely to lower their standards when it comes to short term partners and then show a decrease in attraction following sex (Buss and Schmitt 1993).

Support:

• Buss (1989) cross-cultural study found that women more than men desired mates who were 'good financial prospects' or qualities that were linked to resource acquisition. Men placed more importance of psycial attractiveness and universally wanted mates who were younger than them. Both sexes wanted mates who were intelligent, kind and dependable.
• Clark and Hatfield (1989 and 1990) found men to be more promiscuous and women to be more choosy. 75% of male students who were approached by an attractive female stranger agreed to have sex with them. None of the women approached by attractive male strangers agreed to have sex.
• Buss (1993) males showed greater stress when asked to imagine their partner having sex with someone else. Females showed greater stress when asked to imagine their partner in love with someone else.
• Miller et al (2007) female lap dancers who were in the fertile oestrus phase of their cycle recived almost twice the value of tips compared to girls who were not in oestrus.

Refute

• Male promiscuity and female choosiness can be explained through western social norms.
• Men couldn't have evolved the desire for casual sex without willing females.

AO3

• Determinism: if sexual selection, human behaviour and the relationships it involves are driven by purely evolutionary considerations, they would be incredibly predictable. Human reproductive behaviour has changed a lot over the past century (e.g. increase in same sex relationships, use of contraception, couples not having children by choice). We have more free will than the theory implies.
• Socially sensitive research: some evolutionary psychologists argue that **** is a natural adaption designed to increase reproductive success. This is socially sensitive as it could perpetrate **** culture and encourage the excuse of ****.

Trivers (1972) defines PI as 'any investment by a parent in an offspring that increases the chance that the offspring will survive at the expense of that parent's ability to invest in any other offspring'. The theory claims there are significant sex differences in the type and amount of investment.

• Childbirth became more difficult as brain size of babies increased which led to human children being born prematurley (in relation to other animals). Women have to breastfeed for longer due to this prolonged immaturity. Women make the greater prenatal and postnatal investment.
• Minimum maternal investment is a nine-month pregnancy and years of feeding and carrying whereas the minimum paternal investment was a few moments of copulation and a teaspoon of semen (Symons 1979)
• Males are under pressure to protect themselves from cuckoldry. Because human males make a considerable investment in their children they have a greater concern than females about the fidelity of their mates (Miller 1998)
• Buss (1995) says males are more tuned into sexual jealousy in order to avoid cuckoldy whilst females are more tuned into emotional jealousy in order to avoid a loss of resources and shift in emotional focus.

Support:

• Due to the need for good resources and support as well as good genes, women may engage in extramarital affairs, marrying a man who is caring and provides good resources but have an affair with a man with good genes but no resources. A survery of around 3000 UK women estimates that 14% of the population was a result of extramarital affairs (Baker and Bellis 1990)
• Buss et al (1992) found male students were more likely to be concerned over sexual infidelity whilst females were more likely to be concerned over emotional infidelity.

Dispute:

• There is no proof that the reason the women in Baker and Bellis' survey had extramarital affairs in order to obtain good genes for their offspring.
• In humans, males do restrict their reproductive opportunities and invest more in each child as opposed to producing as many as offspring as possible.