The evolutionary explanations for partner preferences, including the relationship between sexual selection and human reproductive behaviour
- In evolutionary terms natural selection is the process by which certain characteristics and behaviours get passed on in the gene pool because they give the individual a better chance of surviving and reproducing.
- Sexual selection is the process within natural selection where by any characteristic or behaviour that increases the reproductive success of an individual are selected and these characteristics may get exaggerated over evolutionary time.
- Because of the differences in parental investment between males and females, evolutionary psychologists suggest this has created gender specific reproductive behaviour – that is in terms of mating preferences and strategies, and in terms of mating systems (to remain monogamous or is promiscuity best?)
- Because females have to invest a lot of time in having and bringing up offspring, and because the number of offspring they can have in a life time is limited, Darwin suggests this has lead to females being choosy about who they “mate” and settle down with (inter-sexual selection).
- Females will be looking for good genetic qualities in a male and qualities that indicate that he could provide for her and their offspring.
- This in turn has created competition between males (intra-sexual selection). They have to convince females they would be the best to mate with.
- Males will also be concerned with looking for females with qualities that suggest fertility (youth and good health – synonymous with physical attractiveness). Sexual selection may also lead to differences in mating systems. A female may be best in a monogamous relationship which will ensure the male stays and provides for the family. However for a male a polygamy may be better where he mates with as many females as possible thus ensuring quantity in offspring increasing the likelihood of some of them surviving.
- Cross cultural studies provide good evidence for evolutionary theory because if we see the same behaviour across culture we can deduce that this behaviour may be a result of genes (evolution) rather than socialisation.
- Buss, 1989 studied 37 cultures and found that females valued qualities that suggested the financial potential of males – for example ambition and industriousness. On the other hand men valued physical attractiveness and women who were younger than them more than women did. This suggests that they were looking for qualities associated with fertility in line with evolutionary predictions. This was a large scale study with over 10,000 participants which gives it credibility, however it is possible that participants gave the socially desirable answer in terms of what they were looking for in a partner.
- Other studies have supported Buss. For example Waynforth and Dunbar (1995) analysed the content of lonely hearts columns and found that 43% of males sought a youthful mate compared to 25% of females (the younger the female the more fertile). They also found that 44% of males sought a physically attractive partner compared to 22% of females. Finally they found that women “advertise” their physical attractiveness and men advertise their resources. The advantage of this study is that the people writing the adverts would not have been influenced by any investigator effects, however this is a biased sample as only a small proportion of the populations would seek to find partners in this way.
- There is much evidence to suggest that males are more likely to engage in casual sex and engage in polygamous relationships (thus spreading their genes around). For example Clark and Hatfield (1989 and 1990) found that when propositioned by a total stranger 50% of both men and women agreed to go out on a date with the stranger, however none of the females agreed to have sex with a stranger whereas a staggering 75% of males agreed. The study was carried out on a university campus and the participants were students so are hardly representative of the general population. The ethics of this study were also questionable as it involved deception and lack of informed consent and could also have affected the psychological well being of the participants in terms of later guilty feelings.
- Comparative studies of testicle size in primates by Baker and Bellis (1995) also suggest that humans may have evolved under a polygamous mating system. Males have medium sized testicles relative to body size compared to chimpanzees. Chimps live in a promiscuous mating system thus females mate with many males so the male chimp has to have large testes to produce lots of sperm in order to compete. Gorillas are monogamous and have relatively small testes. The medium sized human testes suggest that the norm for our human ancestors was to be mildly competitive so females may have had multiple partners.
- It could be argued that a woman’s best strategy may be to be mildly promiscuous and mate with the man with the best genes but remain with the man who can care and provide. This is supported by Baker and Bellis (1995) who suggested the worldwide rate for mis-attributed fatherhood was 9%.
Issues & Debates
- Evolutionary Approach: Although the studies above lend support to evolutionary theory we must be careful in assuming that human mate choice is just a product of our evolutionary past. Our choices will also be affected by our upbringing, religion and our culture and these may change from generation to generation. Some of the findings of studies can also be explained in terms of culture and society
- Cultural Bias: Evolutionary explanations of mate preference quote a waist-hip ratio of 0.7 in females as being the ideal indicator of fertility and hence an important characteristic of mate choice. However, studies have shown that in isolated populations in Tanzania and Cameroon (Dixson 2007), men consider such ‘hourglass women’ as sickly looking. They prefer a waist-to-hip ratio of between 0.8 and 0.9.
- Real Life: For example in the past women have had to rely on men to provide for them given the inequality in earning power etc. In today’s modern times we may see changes in what women are looking for in a mate. Bereczkei et al (1997) found that females now advertised for men who are family-orientated suggesting they are less concerned about resources.
- Deterministic: Evolutionary theory is also highly deterministic, which is dangerous as we forget that humans have the ability to think about their actions. Biologist Richard Dawkins believes we can override biology with freewill. For example evolutionary theory predicted that men who cannot attract a mate would resort to rape. While this does happen, the majority of single men would not entertain this idea.
- Evolutionary Approach: Finally much of the evidence for evolutionary theory is based on presumed knowledge about past human environments leading to speculations about which behaviours may have been adaptive. As such evolutionary theory is very difficult to test experimentally.