Trivers concept became allot more advanced and it showed that a coherent and plausible way of examining the relationship between parental investment, sexual selection and mating behaviour. He said the sex that invests least will compete over the sex that invests most, and the sex that invests most will have more to lose by a poor match and so will be choosier over its choice of partner. Using this definition Trivers concluded that the optimum number for each parent would be different.
Clutton-Brock and Vincent (1991) said that the way of understanding mating behaviours is to focus on the potential offspring production rate of males and females. They suggested that it is important to identify the sex, which is acting as a ‘reproductive bottleneck’ for the other. In mammals it is the involvement in gestation and nurturing that places limitations on the reproductive output of females. Humans are different in this point of view as the range of parental investment possible by a male ranges from near zero to equal or more than the female could bear.
Bus (1992) based his arguments on cross-cultural studies from 33 countries, states that men value physical attractiveness more than do women while women are more likely than are men to value good earning potential and high educational and occupational status. When offered a list of characteristics from which to choose, women tend to choose such attributes, as ‘good financial prospects’ while men tend to opt for good looks as essential criteria.
Bus did an experiment into sex differences in jealousy. To test for sexual differences in of jealousy he issued questionnaires to undergraduates at the University of Michigan, asking them to rank the level of distress caused by either the sexual or emotional infidelity of a parent. The results suggested that men tend to be more concerned about sexual infidelity and women amore about emotional infidelity. The same effect was then observed when subjects were ‘wired’ up and tested for physiological responses to the suggestion that they imagine their partner behaving unfaithfully either sexually or emotionally. He found that men consistently and significantly showed heightened distress to thoughts of sexual infidelity compared to emotional. These results can be related to the evolutionary theory that suggests that women need to choose the right male and also they way in which people compete for the opposite sex (competition between men) this is called intra sexual selection.
This experiment can give us some good information sex differences in jealousy but the way it was carried out using a questionnaires is not always the best way as they can be biased. Also this sample cannot be representative.
Parental investment can explain many of these features; Men tend to favour polygamy as a mating system. Women are more likely to favour monogamy but may be satisfied with other arrangements depending on the circumstances. Physical characteristics are by far the most important determinant of female sexual attraction whereas power and economic status make a man attractive to women. Male jealousy tends to focus on sexual rather than emotional infidelity and in most societies male adultery is much more likely to be tolerated than female unfaithfulness. Even though these observations can be explained in evolutionary terms but it does not mean that this is the correct explanation even though they can be difficult to falsify but still evolution can be seen from a totally different view that explains the way some unpleasant human characteristics as just human, ignoring social factors.
Whilst there has been research particularly that of Buss, which supports predictions made by Parental Investment Theory there are problems with these in terms of the representative nature of the sample, methods employed, and shared attitudes and beliefs which play a vital role in establishing and maintaining a relationship.
