Assess the Relationship Between Sexual Selection and Human Reproductive Behaviour

Assess the relationship between sexual selection and human reproductive behaviour. (24 marks)
The nature of sexual selection is derived from the evolutionary theory. This suggests that the people who we choose to have sex with has been born into us and is an innate response we have. It also suggests that all behaviours are adaptive, including relationship formation, therefore forming a relationship should help out ‘survival’ in the way of passing on our genes.
There are 2 types of sexual selection, of inter and intra. Intra-sexual selection is when there is competition within one sex (usually males) to compete with each other for access to the members of the opposite sex. Then whoever wins will be able to pass on their genes in reproduction and the traits of successful reproduction will be passed on. There is also intersexual selection which is the selection of particular traits in the mate of the opposite sex. This means that the preferred choice of one sex will determine the areas the other sex has to compete in. For example if all females prefer tall men then over time, there will be an increase in tall males since the tall characteristics will be passed onto offspring when tall males are chosen. These selection pressures would suggest that we need to form heterosexual relationships in order to reproduce our genes and ensure survival of those genes that are vital for survival, through the generation.
Humans have also developed strategies for short term mating. According to the parental investment theory, men have a greater desire for casual sex and it occurs earlier in the relationship, women are not the same. Buss and Schmitt found males lower their standards for these short-term opportunities, after which a rapid decrease in sex drive means they depart quickly to move onto the next female. This would mean that males would be able to have many short-term sexual relationships since he is moving on quickly and increasing the chance of his genes being passed on.
Clarke and Hatfield (1989) found evidence that men have evolved psychological mechanisms to ensure success in short term mating. Experimenters approached strangers of the opposite sex and asked them wither they will go on a date, go to their apartment, or have sex with them. 75% of men agreed to have sex whereas 0% of females agreed to have sex. This shows that men do have a greater desire for casual sex since it is a chance for them to pass on more copies of their genes to potential carriers of their offspring. Men have evolved to become different to women but still ensured their success in short term mating.
Long term mating preferences results in both sexes having high levels of choosiness to then invest heavily on the offspring. As females biologically invest, they are naturally more picky, looking for someone who can invest resources also being a good parent and partner to protect the offspring. Good compatibility would reduce the overall costs to her and the children. Males have also been shown to like younger women, as it’s a sign of fertility.
Buss’s (1989) studied over 10,000 people of 37 cultures, found that men wanted physical attractiveness and mates who were younger than them. They also found that both sexes wanted intelligence in their long term partner. The study shows that men do look for the most fertile women to ensure a successful reproduction and passing on genes to the offspring, since they are looking for mates who were younger than them. Furthermore, intelligence is an indication of skills that is linked to parenting, but also kind and dependent which are associated with reliability in long-term relationship. Since both sexes are looking for intelligence in their partner then this is further evidence to support the long-term mating preferences and intersexual selection that occurs, they both happen to ensure the protection of the child once it is born and that it will be carefully looked after.
Fertility is important in a mate choice, but since oestrus is hidden in humans, how will men know when a woman is at her most fertile? In most mammalian species, the female gives out a variety of visual or chemical signals, which encourage the male to mate. Miller et al. (2007) calculated the tips earned by lap dancers at varying stages of their menstrual cycle. They found that those who were in the fertile oestrus phase of their cycle earned almost twice the value of tips compared to girls who were not in their oestrus. This supports how men choose the most fertile woman for their long-term mate. However, this study was completed on lap dancers and it is not likely that the men will look for lap dancers as their long term partner since they will not have all the long term mating preferences that males will look for. This study does support the short-term mating strategies that men have since they are not able to see when a woman is most fertile, they will just keep having sex until a child is conceived, either with the same woman or not.
This theory is too deterministic because it assumes that all humans want their genes passed on to survive. It is not able to explain prostitution when men will be using contraceptives which will hinder them from passing on their genes. Also there will be many other cases when people marry someone who is infertile, physically disabled or with a genetic abnormality. This would suggest that their genes are not the best and a successful offspring can’t be secured but the relationship is still formed. So surely there must be another factor which influences who we choose during sexual selection, other than us choosing who can help us pass on genes.
The theory is also too simplistic to explain step-families since the parents are raising non-biological children. This could be seen as the parents ‘wasting’ their resources on non-relatives. Raising step-children would mean that they are investing to raise someone else’s genes and not their own. The theory would suggest that the they shouldn’t be raising and wasting their investment and go have their own biological children to expend their resources on, to make sure that their genes are passed on and surviving. Even though the children are not their own, the parents will still go to great lengths to protect their child.