Evolutionary Explanations For Partner Preferences

What is sexual selection?

An evolutionary explanation of partner preference. Attributes or behaviours that increase reproductive success are passed on and may become exaggerated over succeeding generations of offspring.

What does Darwin’s concept of sexual selection concern?

The selection of those characteristics that aid successful reproduction (rather than survival).

What are some physical characteristics, such as a male peacock’s tail a sign of?

Physical fitness,

What do females who select males with such characteristics (ie a male peacock’s tail) much more likely to produce?

Robust offspring and therefore the preference for such a tail is perpetuated in future generations.

Why are other characteristics, like aggressiveness adaptive?

Because they provide an advantage for a male over competitors for reproductive rights. These aggressive characteristics that allowed the animal to reproduce are passed on to offspring if they are genetically determined and the genes that gave rise to the characteristics remain in the population.

What is the basis of human reproductive behaviour?

Anisogamy.

What does anisogamy refer to?

The differences between male and female sex cells (gametes).

What are male gametes (sperm)?

Small, highly mobile, continuously created in vast numbers from puberty to old age and do not need much energy to be produced.

What are female gametes (eggs or ova)?

Relatively large, static, produced at intervals for a limited number of fertile years and require a significant investment of energy.

What is one consequence of anisogamy?

There is no shortage of fertile males but a fertile female is a much rarer ‘resource‘.

Why is anisogamy important in partner preference?

Because it gives rise to two types of sexual selection?

What is inter-sexual selection?

Between the sexes - the strategies that males use to select females or females use to select males.

What is inter-sexual selection the preferred strategy of?

The female, quality over quantity (eggs are rarer than sperm).

What did Trivers point out?

That a 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 loose if they invest resources in substandard partners.

Since the consequences of making a wrong partner choice more serious for the woman, what must she be?

Especially selective. Therefore, the female’s optimum mating strategy is to select a genetically fit partner who is able to provide resources.

What does female preference determine?

Which features are passed on to the offspring. For example, if height is considered an attractive trait by females then it would increase in the male population over successive generations. This is because, in each generation, females will select the tallest males and thus that characteristic gradually becomes exaggerated (a runaway process).

What did Fisher develop?

A sexy sons hypothesis.

What does Fischer’s sexy sons hypothesis state?

That 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.

What is intra-sexual selection.

Within each sex - such as the strategies between males to be the one that is selected.

What is the preferred strategy of the male?

Intra-sexual, as quantity over quality (there is a plentiful supply of sperm).

What is there competition between males for?

To be selected to mate with a female. The winner of the competition reproduces and therefore the characteristics that contributed to this victory may be passed on to his offspring.

What has intra-sexual reaction given rise to?

Dimorphism (meaning ‘two forms‘) - males and females end up looking very different because of intra-sexual selection.

What is an example of intra-sexual competition within males?

In any physical competition, 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.

In females, why is youthfulness selected?

Because males have a preference to mate with younger, more fertile women.

What consequences does intra-sexual selection have?

Behavioural ones, although these are controversial.

How does intra-sexual selection have behavioural consequences?

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). This leads to the selection of aggressiveness in males.

What are the strengths of the evolutionary explanation of preferences?

• Research support for inter-sexual selection.

• Research support for intra-sexual selection.

How is the research support for inter-sexual selection a strength of the evolutionary explanation of preferences?

There is evidence supporting the specific role of female choosiness in heterosexual partner preference: Clark and Hatfield sent male and female psychology students out across a university campus. They approached other students individually with this question: 1 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.

What does the research support for inter-sexual selection support?

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.

What is the counterpoint to the research support for inter-sexual selection?

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) 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.

What does the counterpoint to the research support for inter-sexual selection mean?

This is a more complex and nuanced view of how evolutionary pressures influence partner preferences which takes account of the context of reproductive behaviour.

How is research support for intra-sexual selection a strength of the evolutionary explanation of preferences?

Buss 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.

What does the research support for intra-sexual selection mean for the evolutionary explanation of preferences?

These findings reflect consistent sex differences in partner preferences and

support the predictions from sexual selection theory.

What is the limitation to the evolutionary explanation of evolutionary explanation of preferences?

Social and cultural influences underestimated.

How is social and cultural influences being underestimated a limitation of the evolutionary explanation of preferences?

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). Bereczkei et al. argue that this social change has consequences for women's mate preferences, which may no longer be resource-oriented

What does social and cultural influences being underestimated mean for the evolutionary explanation of preferences?

That 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.