Sexual Selection And Human Reproductive Behaviour Flashcards
What is anisogamy?
This is the difference between male and female sex cells. Male cells (sperm) are small, mobile and continuously produced from puberty to old age. Female cells (ova) are larger, static and produced for a limited number of years.
How is anisogamy related to mating strategies?
Consequences of anisogamy are that there are plenty of fertile males but fewer females. This gives rise to different mating strategies - inter-sexual and intra-sexual.
What is inter-sexual selection?
This is the selection of mates between sexes (e.g. Females selecting males or males selecting females).
What is the female strategy of inter-sexual selection?
This is quality over quantity. Females make a greater investment of time, commitment and other resources before, during and after birth. Need to be choosier than males so seek a male who will provide healthier offspring and support them with resources.
What is the impact of inter-sexual behaviour on mating behaviour?
Preferences of both sexes determine attributes that are passed on - e.g. If height is a genuine marker of fitness in males, the females who choose the tallest males will have greater reproductive success and innate preferences are passed on. Over time this leads to taller and taller men being selected (runaway process).
What is intra-sexual selection?
This is the selection of mates within sexes (e.g. Males competing with other males for mates).
What is the male strategy for intra-sexual selection?
This is quantity over quality. Males do best if they reproduce as frequently as possible. Competition is necessary as females are a limited resource and are choosy. Males who compete successfully pass on their genes to the next generation and therefore those traits are perpetuated.
What is the impact of intra-sexual selection on mating behaviour?
Intra-sexual selection pressures lead to certain patterns of human behaviour:
- Male aggression - the most aggressive males are more likely to reproduce.
- Male preference for youthful and fertile women because these are signs of fertility leading to reproductive success.
Strength: support for the relationship with intra-sexual selection.
Buss surveyed over 10,000 adults in 33 countries asking about partner preference. He found that females valued resource-related characteristics more than males (e.g. Good financial prospects). Males valued reproductive capacity (e.g. Good looks and youth). This supports sex differences due to anisogamy and partner preferences derived from sexual selection theory.
Strength: support for the relationship with inter-sexual selection.
Clark and Hatfield sent students to approach other students and ask ‘I have been noticing you around campus. I find you to be very attractive. Would you go to bed with me tonight?’ No female students agreed in response to requests from males. But 75% of males did agree to female requests. This supports the suggestion of female choosiness and that males have evolved a different strategy to ensure their reproductive success.
Limitation: the relationship ignores social and cultural differences.
Partner preferences have impacted over time by changing social norms and cultural practices. These have occurred too rapidly to be explained in evolutionary terms. Chang et al. report that some preferences have changed and others have remained the same over 25 years in China. This suggests that both evolutionary and cultural influences must be taken into account when explaining human reproductive behaviour.
Strength: support from waist-hip ratio research.
Singh measured waist-hip ratio (WHR) preferences of males for females. Findings were that any hip and waist size can be attractive as long as the ratio of one to the other is 0.7 (thought to signify that the female is fertile but not currently pregnant). This shows that evolutionary factors are reflected in patterns of human reproductive behaviour through partner preferences.
Strength: support from lonely hearts research.
Waynforth and Dunbar studied lonely hearts advertisements in American newspapers to see how men and women describe the qualities they desired in and offered to a potential partner. They found women tended to offer physical attractiveness and indicators of youth and sought resources. Men offered resources and sought youth and physical attractiveness. These findings support the evolutionary suggestions that women will seek resources whilst men are more focused on signs of reproductive fitness.
