- The evolutionary perspective on relationships argues that human reproductive behaviours have their origins in the evolutionary past and exist because they conveyed survival or reproductive advantages to our distant ancestors.
- Trivers’ (1972) parental investment theory argues that differences between males and females have their origins in the different amount of parental investment made by males and females.
- For humans, the male investment in offspring is relatively small. He is fertile throughout his life and has large amounts of sperm, and so is capable of many matings. The amount of offspring he can produce depends entirely on the amount of available female partners, and the act takes little in terms of time and energy. However the female’s investment in each offspring is far more substantial. She has limited amounts of gamete, typically producing one ovum per month, and her reproductive life is reduced to about 30 years. This severely limits the total number of offspring she can reproduce in a lifetime.
- The female must also put in a lot more time and energy than the male, following conception she must carry a growing foetus for around 40 weeks, feeding it from her own supplies of nourishment. She must then give birth and continue to invest in the baby, in the past this would have included breastfeeding for at least 2 years although this is not always necessary any more.
- Her investment however in comparison to the males is extensive and so her best chance of reproductive success is to ensure the survival of her children. Whereas the best chance of a male’s reproductive success is to simply have many matings with multiple fertile partners.