Noe & Hammerstein have likened the process of sexual selection to a ‘biological market-place’. Because it is highly unlikely that individuals will get exactly what they want, mate choice can be seen as a trade-off between what an individual wants and the demands of the pool of potential mates. This means that individuals in a strong bargaining position (.i.e. they possess desirable qualities) can increase their demands and become more selective. On the other hand, those who have fewer of these desirable qualities are in a weaker position and might have to lower their demands as a consequence (i.e. become less selective). A good insight into the mating strategies of men and women can be gained from studying the nature of personal advertisements. Evolution theory would predict that men and women would advertise the qualities that have evolved to give them the best chance of attracting the most appropriate mate which virtually every study conducted on personal advertisements have found. Youth and beauty and men with good resources were higher in demand, supporting the notion of the biological marketplace.
Waynforth & Dunbar found that the sexes tended to use different kinds of descriptions in their search for a partner. Female advertises appeared concerned with wealth and commitment in prospective mates, whilst male preferences in their advertisements tended to reflect female fecundity. They also found evidence for advertises adjusting descriptions according to how they perceived their status in the market place, as predicted by the economies of the biological market place. However, as the study was carried out in the USA, it is important to ask if the preferences appear to be culture specific or if they are the same across cultures. Others have assessed partner preferences of homosexual people. Bailey & Zucker looked at the preferences of both gay and straight men and found them to be very similar. Both showed a large amount of interest in the physical attractiveness of their partner and in uncommitted sex. Both types on men were relatively uninterested in the financial status of potential partners.
INTRA-SEXUAL SELECTION
One consequence of males competing with each other for access to mates is sexual dimorphism. This refers to the observations that, in many animal species were there is intrasexual competition; the male looks different from the female. Human males for example are on average 12/15% larger than human female. The great apes show greater sexual dimorphism with the males being up to 50% bigger than females. Sexual selection accounts for a great deal of dimorphism, most frequently seen as secondary sexual characteristics. In animals they take many forms, such as the long tail feathers of the peacock or the manes of lions. Examples in females include the reddening of female rhesus monkey hindquarters and smooth pectoral fins in carp. In human males it includes size (.e.g. height and physique) , facial hair and deepening voice; while in women it includes enlargement of breasts and changes in body fat distribution (.i.e. widening hips) and smooth hairless skin. Secondary sexual characteristics are honest indicators of male reproductive fitness, as they are not expressed to the same degree in unfit males. Unfit males don’t seem to be able to tolerate the physical investment that the developments of secondary sexual characteristics require. The testosterone levels needed to promote their development suppress immune system functioning and therefore increase the chances of disease and illness. Consequently. Only males in prime condition are able both to develop and to carry these features. This makes them particularly attractive to females who are looking for good genes in potential mates.
Differences in reproductive behaviours
As well as differences in partner preferences we can also consider human reproductive behaviour differences. Whilst there are clearly many similarities between male and female behaviour, there are also some fairly clear differences: For instance, the tendency to engage in casual sex. (Buss & Schmitt) On balance, men tend to be much likely to have short-term relationships or on-night stands then women. This was demonstrated beautifully in Clark & Hatfield’s studies where a sample of male and female students approached strangers of the opposite sex on campus and asked them either to: go out with them that night, go back to their house with them or to have sex with them. They found that 50% of men and women agreed to go out with them that night, but no women agreed to have sex with them. However 75% of men agreed to have sex although only 69% agreed to go back to their house. Even when Clark modified the study in 1990 and assured participants about the trustworthiness of the strange the results were still the same, women did not generally agree to casual sex. The general unwillingness to engage in uncommitted sex is also found in lesbians. (Buss and Schmitt)
Buss & Schmitt also found that men tend to seek and desire a greater number of sexual partners then women. They asked how many sexual partners people would ideally like over the next two years, the next decade and during their lifetime. On average, men would like 8 partners over the next 2 years compared to women’s 1 partner. Over a life time, averages were 18 for men and between 4 or 5 for women.
Research has also found differences in sexual jealousy. Whilst both men and women feel jealousy at betrayal by a partner, evidence shows us that what makes them jealous maybe different. Buss asked male and female students to imagine their current boy/girlfriend either having sex with someone else or in love with them. Whilst engaging in these rather strange fantasies, they wired up to measure stress responses. The researchers found men became more distressed at the image of their partner being sexually unfaithful, whereas women became most distressed at the idea of their partner in love with someone else. Schutzwohl replicated this study asking students to make a choice between sexual and emotional infidelity in their partner. He measured their decision times to response and found that those who selected the adaptive response took less time than those who selected the less adaptive approach. Sexual fantasies and dreams is also more common in men than women especially those involving multiple or anonymous partners and strangers (Ellis & Symons)
Many of these studies carried out in this area have significant ethical implications. For example, Clarke and Hatfield’s study on university campuses involved deception and a lack of informed consent. The studies carried out by Buss and Schmitt and Schutzwohl into sexual jealousy involved some degree of stress and emotional distress by their very nature, even though participants consented to take part. There are also issues of demand characteristics. In Buss and Schmitt’s study, it’s likely that participants were influenced to produce social desirable answers, and it may be easier or more socially acceptable for men to report sexual dreams and fantasies then women.
Evolutionary theory sees these preferences and behaviours as originating through the processes of sexual selection. Sexual selection operates on similar principles to Darwin’s natural selection. Darin was initially puzzled by bodily features such as the male peacocks spectacular tail, which appeared to offer no survival value and indeed made the peacock much more vulnerable to predictors as it hampered the bird’s ability to fly. However, the peacock’s long and glorious tail was found to be valued by peahens that actively preferred mates with beautiful tails. In order to explain this, Darwin proposed the concept of sexual selection, suggesting that some bodily features and behaviours exist because they are valued by the other sex and are deemed attractive, this leading to increased opportunities for mating.
The idea that animals develop preferences for characteristics which have no particular evolutionary adaptive value has also been explained by the ‘sexy sons’ hypothesis (Fisher) for instance again using the example of the male peacocks spectacular tail; this trait is seen as ‘sexy’ to peahens therefore if this trait is passed on to her male offspring, these sons are more likely to be selected as mates. By producing ‘sexy sons’ who will be desired by other females, he parent is enabling its genes to be passed on to future generations. Other generations of mate selection, this characteristic will become more and more pronounced, this is known as the ‘runaway’ process. The process only stops through a balance with natural selection (the train becomes too costly) or a change in female preference.
Zahavi’s handicap process suggests that males who survive in spite of having a ‘handicap’ will be genetically superior to other males. For instance, a woman may select a partner not because he drives an expensive car but because he still manages to survive even though he has the handicap of running an expensive car. It may be that women who prefer ‘handicapped’ males are selecting those who have good survival genes. Again using the example of the peacock, even though its large tail may weaken its chance of survival as it’s most noticeable to predators, it may serve as a ‘badge’ of healthiness.