evolutionary explanations for partner preferences Flashcards
What is Darwin’s concept of sexual selection?
Darwin’s (1871) concept of sexual selection refers to the selection of characteristics that aid reproduction rather than survival.
• Examples: Features like a male peacock’s tail signal genetic fitness. Females who select mates with such traits are more likely to produce offspring who inherit those traits.
• Adaptive Traits: Characteristics like aggression give males an advantage over competitors for reproductive rights.
• Mechanism: Traits that promote reproduction are passed on if genetically determined, ensuring these traits persist in the population.
What is anisogamy, and why is it important for sexual selection?
Anisogamy refers to the differences between male and female gametes:
• Male Gametes (Sperm): Small, mobile, produced in vast quantities continuously from puberty to old age with low energy costs.
• Female Gametes (Eggs): Larger, static, produced at intervals for a limited number of fertile years, and require significant energy.
• Consequence: While there is no shortage of fertile males, fertile females are a “resource” sought after in reproductive selection. This gives rise to inter-sexual and intra-sexual selection.
What is inter-sexual selection, and how does it relate to sexual selection?
Definition: Inter-sexual selection is between the sexes, where one sex (usually females) selects a mate based on specific traits. It is the preferred reproductive strategy for females due to their greater investment in offspring.
• Robert Trivers’ Theory: Females invest more in their offspring, so they prefer genetically fit partners who can provide resources.
• Outcome: Over generations, female preferences for traits like height or attractiveness increase the presence of those traits in the male population (e.g., tall males passing on their height).
• Example: Ronald Fisher’s sexy sons hypothesis explains that females mating with males with desirable traits ensure their sons inherit those traits, making them more likely to reproduce.
What is intra-sexual selection, and how does it differ from inter-sexual selection?
Definition: Intra-sexual selection occurs within the same sex, with males competing for access to females. It is the preferred strategy for males due to the plentiful supply of sperm.
• Competition: Males compete to be selected by females, and the “winner” passes on traits that helped him succeed, while “losers” do not reproduce.
• Dimorphism: Intra-sexual selection leads to differences between males and females:
• Males often develop traits like larger size and strength.
• Females are typically smaller and less physically competitive.
What behavioral and physical traits are shaped by intra-sexual selection?
Physical Traits:
• Larger males are better equipped to outcompete rivals and are more likely to mate.
• In humans, females may prefer males with secondary sexual characteristics (e.g., broad shoulders, a high waist-to-hip ratio).
Behavioral Traits:
• Aggressiveness and risk-taking behaviors increase chances of reproductive success.
• Retention Strategies: These include guarding mates to prevent competition.
How do inter-sexual and intra-sexual selection differ in their strategies and outcomes?
Inter-Sexual Selection:
• Involves mate choice by one sex (usually females).
• Focuses on selecting genetically fit, resourceful partners.
• Traits like attractiveness and ability to provide resources are favored.
Intra-Sexual Selection:
• Involves competition within one sex (usually males).
• Focuses on traits that enhance success in physical or social competition (e.g., size, strength, aggression).
• Leads to dimorphism (physical differences) between sexes.
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.
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 sex differences in partner preferences and support the predictions from sexual selection theory.
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.
