evolutionary explanations for partner preference Flashcards
(8 cards)
sexual selection
Darwin’s (1871) concept of sexual selection concerns the selection of those characteristics that aid successful reproduction (rather than survival). Some physical characteristics, such as a male peacock’s tail, are a sign of genetic fitness. Females who select males with such characteristics are more likely to produce robust offspring and therefore the preference for such a tail is perpetuated in future generations. Other characteristics, such as aggressiveness, are adaptive because they provide an advantage for a male over competitors for reproductive rights. The aggressive characteristics that allowed the animal to reproduce in the first place are passed on to offspring if they are genetically determined and the genes that gave rise to the characteristics remain in the population.
influences on human reproductive behaviour-anisogamy
The basis of human reproductive behaviour is anisogamy, which refers to the differences between male and female sex cells (gametes). Male gametes (sperm) are small, highly mobile, created continuously in vast numbers from puberty to old age and do not need much energy to be produced.
In contrast, female gametes (eggs or ova) are relatively large, static, produced at intervals for a limited number of fertile years and require a significant investment of energy.
One consequence of anisogamy is that there is no shortage of fertile males but a fertile female is a much rarer resource. Anisogamy is important in partner preference because it gives rise to two types of sexual selection.
inter-sexual selection
Inter-sexual selection is between (inter) the sexes - the strategies that males use to select
id mate
females or females use to select males. Inter-sexual selection is the preferred strategy of the female, quality over quantity (ova are rarer than sperm).
Robert Trivers (1972) pointed out that the female makes a greater investment of time, commitment and other resources before, during and after the birth of her offspring. Both sexes are choosy, because both stand to lose if they invest resources in substandard partners. But the consequences of making a wrong partner choice are more serious for the female, so it pays for her to be especially selective. Therefore, the female’s optimum mating strategy is to select a genetically fit partner who is able to provide resources.
It is this female preference which determines which features are passed on to the offspring. For example, if height is considered an attractive male trait by females then it would increase in the male population over successive generations. This is because, in
becomes exaggerated (a runaway process).
each generation, females will select the tallest males and thus that characteristic gradually Ronald Fisher (1930) developed a sexy sons hypothesis - the genes we see today are those that enhanced reproductive success. A female who mates with a male who has a certain characteristic then will have sons who inherit this ‘sexy’ trait. Then her sons are also more likely to be selected by successive generations of females who will mate with her offspring. Therefore the preference for this ‘sexy’ trait is perpetuated.
intra-sexual selection
Intra-sexual selection is within (intra) each sex - such as the strategies between males to be the one that is selected. It is the preferred strategy of the male, quantity over quality (there is a plentiful supply of sperm).
There is competition between males to be selected to mate with a female. The winner of the competition reproduces and therefore the characteristics that contributed to his victory may be passed on to his offspring (and losers do not pass on their losing’ characteristics because they don’t mate).
This strategy has given rise to dimorphism (means ‘two forms’) - males and females end up looking very different because of intra-sexual selection. For example, in any physical competition between males, size matters. Larger males have an advantage and are therefore more likely to be reproductively successful. On the other hand, females do not compete for reproductive rights so there is no evolutionary drive towards favouring larger females. However, in females youthfulness is selected because males have a preference to
mate with younger more fertile women (as indicated in humans by, for example, a large waist-to-hip ratio).
Intra-sexual selection also has behavioural consequences, although these are controversial. The characteristics that are favoured and passed on are those that allow a male to outcompete his rivals, including deceitfulness, intelligence and aggression. For example, males may benefit from behaving aggressively in order to acquire fertile females
and protect them from competing males (mate retention strategies, see page 298). This
leads to the selection of aggressiveness in males.
s-research support for inter sexual selection
One strength is evidence supporting the specific role of female choosiness in heterosexual partner preference.
Russell Clark and Elaine Hatfield (1989) sent male and female psychology students out across a university campus. They approached other students individually with this question: I have been noticing you around campus. I find you to be very attractive. Would you go to bed with me tonight?. Not a single female student agreed to the request, whereas 75% of males did, immediately.
This supports the view that females are choosier than males when it comes to selecting sexual partners and that males have evolved a different strategy to ensure reproductive success.
Counterpoint The argument from sexual selection that one strategy is adaptive for all males and another is adaptive for all females is simplistic. At the very least it appears that strategies differ according to the length of the relationship. Sexual strategies theory (Buss and Schmitt 2016) argues that both males and females adopt similar mating strategies when seeking long-term relationships. Both sexes are very choosy and look for partners who are loving, loyal and kind, for example.
This is a more complex and nuanced view of how evolutionary pressures influence partner preferences which takes account of the context of reproductive behaviour.
strength-research support for intra sexual selection
Another strength is evidence to support the predictions of sexual selection theory.
David Buss (1989) carried out a survey of over 10,000 adults in 33 countries.
He asked questions relating to a variety of attributes that evolutionary theory predicts are important in partner preference. He found that females placed greater value on resource-related characteristics than males did, such as good financial prospects and ambition. Males valued physical attractiveness and youth (as signs of good reproductive capacity) more than females did.
These findings reflect consistent sèx differences in partner preferences and support the predictions from sexual selection theory.
research limitation-more complex
Mate choice may be more complicated than suggested by this approach.
Research by Penton-Voak et al. (1999) suggests that females’ mate preferences change across the menstrual cycle.
They found that females preferred a partner with strongly expressed masculine features during their fertile period, but showed more preference for a partner with slightly feminised features as a long-term mate. This may be because masculine appearance suggests a healthier immune system, which would be advantageous to pass to offspring, while slightly feminine features suggest kindness and parental cooperation - very desirable traits in a long-term partner!
These finding suggest that mate choice may actually be based on a range of factors, rather than simply indicators of genetic fitness.
l-social and cultural influences underestimated
One limitation is that evolutionary theories overlook the influences of social and cultural factors on partner preference.
Partner preferences over the past century have undoubtedly been influenced by rapidly changing social norms of behaviour. These develop much faster than evolutionary timescales imply and have instead come about due to cultural factors (e.g. availability of contraception). Women’s greater role in the workplace means they are no longer dependent on men to provide for them (despite the ongoing inequality in earning power). Tamas Bereczkei et al. (1997) argue that this social change has consequences for women’s mate preferences, which may no longer be resource-oriented.
Therefore, partner preferences today are likely to be the outcome of a combination of evolutionary and cultural influences. Any theory that fails to account for both is a limited explanation.
