The biological market place - Noe and Hammerstein (1995):
It's unlikely that we will get exactly what we want and so mate choice is a trade-off between individual demands and those of available potential mates. E.g. the more desirable traits we have, the stronger our bargaining position, therefore the more choosy we can be, and vice-versa.
Research with personal adverts has found that women with youth and beauty and men with resources are most in demand.
Waynforth and Dunbar (1995) claimed that courtship in humans is influenced by the same rules that govern sexual selection in non-human animals. They studied 479 adverts placed by men and 402 by women.
Men of 40-49 (maximum personal resources) expressed preferences of physical attractiveness whilst women (especially women in their peak reproductive years 20-39) demanded wealth 4.5 times more often than men did.
Supported by Campos et al (2002) who found as women aged their adverts became less demanding in their mate selection, whilst males became more demanding.
However, Strassberg and Holly (2003) placed `female seeking male` adverts, differing slightly in wording, on personal bulletin boards on the internet. The most popular advert was where the woman described herself as `financially independent, successful and ambitious`, contradicting other research.
Intrasexual selection:
Intrasexual selection takes place when males compete (often aggressively) and the winner is rewarded with the female. The female is passive in this process - she doesn't choose her own mate.
Research of Male Aggression
Daly and Wilson (1988) - 90% of male murders involve men of mate-competition age.
Buss and Dedden (1990) - Female verbal aggression is an attempt to reduce the apparent attractiveness of their competitors in the eyes of the males.
Sperm competition:
When sperm from two or more males compete to fertilise an egg, especially in promiscuous species (like humans) where there is sex with multiple partners.
Males protect their investment in females carefully, ensuring that theirs is the only sperm to reach the egg of the female.
Male testis size
Large testes evolved due to female infidelity rather than to fertilise widely, since large quantities of sperm would not be needed if females could be trusted.
Evidence:
- The more sperm competition, the larger the testes relative to body weight.
- Humans have less sperm competition than chimpanzes so have evolved smaller testicles, producing fewer sperm.
Sperm allocation:
Where there are lots of opportunities to copulate, being economical with sperm increases the chance of reproducing, as the amount of sperm available decreases with each copulation.
Evidence:
- In species with more females than males, there is less sperm in each ejaculate, and where there are fewer females there is more sperm in each ejaculate.
- Packer and Pusey (1983) - a male lion may copulate up to 100 times a day but only ejaculate a limited number of sperm each time.
Female orgasm:
Female orgasms are not necessary for conception. The contractions during orgasm help to pull the sperm nearer to the egg: this improves the chance of conception and ensures that males with best indicators of fitness are favoured.
Study
- Shackleford et al (2000) - The female orgasm is designed for discriminating male quality.
- 388 US and German heterosexual females in committed relationships responded to a questionnaire about their partner and relationship.
- They found that those who were with more attractive men were more likely to reach orgasm during copulation.
Study
- Pollet and Nettle (2009) - using a large representative Chinese survey sample, found that frequency of female orgasm increased with partner's income.
- This could not be explained by age, happiness, health and educational achievement among other things.
- Female orgasm is an adaptive response promoting conception with higher quality males.
Explanations of female mate choice:
Two theories have been proposed to explain why females are choosier than males.
`Sexy sons` hypothesis (Fisher, 1930)
- Populations could develop preferences for certain characteristics (tallness, muscular physique).
- Mating with these individuals means that the characteristics are passed on to the next generation.
- Eventually these characteristics become the norm.
- By creating these `sexy sons`, who will be desired by others, the female ensures her genetic material is passed on to those with whom her sons mate.
- Over generations of mate selection the characteristics will become more pronounced - the `runaway` process, which only stops when the characteristic becomes too costly or females change preference.
Handicap process (Zahavi, 1975)
- Males who survive in spite of having a handicap are generally superior to other males (e.g. the expense of driving a Ferrari handicaps the man economically, but he still manages to survive and so is more attractive to women).
- Such `handicaps` could be seen as a `badge` of healthiness and be attractive to females.
Parasite-mediated sexual selection:
- Maintaining a healthy immune system is very costly for the body, but essential for survival, e.g. a defence against effects of parasites.
- However, immune functioning is worsened by the effects of testosterone.
- Males with the best secondary sexual characteristics are showing high levels of reproductive fitness since they are maintaining these features whilst remaining strong and healthy.
- Females therefore select males because of the male handicap of superior secondary sexual characteristics.
General criticisms of evolutionary explanations of human behaviour:
1. Men are more fertile than women and higher status men are preferred by females - This is a gross over-generalisation. Not all men are more fertile than women and not all women prefer high status males. These are behavioural trends only.
2. Evolutionary principles are the same for all animals - While this is indeed true, evolutionary principles often ignore or underestimate social and cultural factors.
3. The principal drive is to procreate - It is not for homosexuals. How does evolution explain the increase in, and indeed increased acceptance of, homosexuality? Also, many women choose not to have children.
4. Evolution just makes perfect sense - True. However, it is largely unfalsifiable. Often the theory is adjusted to fit any findings that do not agree with it, making it extremely difficult or impossible to falsify.
5. Females choose male mates on the basis of their economic resources - Not necessarily. Weiderman and Alllgeier (1992) say that this is a perfectly rational choice. Men tend to be richer than women! Evolution is very hard to test in controlled conditions and so we can never be sure whether alternative explanations like this are any better than the evolutionary explanation.
6. Infertile people should be disinclined to have sex. There is no point in doing so in terms of adaptation - Not true at all. Infertile people enjoy sex as much as, or more than, fertile people. In many cases they do not have the concern about whether their actions may result in unwanted pregnancies.
7. Women are more likely to be monogamous, certainly after reproducing, and they will choose older, more resource-rich males as partners - Not necessarily true. Women are often unfaithful, and often choose younger men than themselves. Men often choose older women even though they know they cannot provide them with young.
by
thenainoji (student)
