Chapter 7: Evolution by natural selection
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Evolution by natural selection:
- Charles Darwin theory:
a) Individuals differ in various characteristics
b) These characteristics are to some extent transmitted directly – through
reproduction itself – from parents to offspring
c) Some characteristics are associated with greater numbers of surviving
offspring – reproductive success
d) Across generations, those characteristics will become more widespread among
the individuals of the population
- Individual differences among people
- Inheritance of characteristics
- Characteristics associated with reproductive success
- Changes across generations in levels of characteristics
How is variation maintained among humans?
- The variation in personality and physiological traits are unimportant to survival
- The importance of variation in combating infections by parasites. It is harder for
parasites to enter a body and infect it in a large population when there is much
• Fluctuating optimum: why would variation in a trait be maintained across long
periods of time, why would one ideal level of the trait not simply defeat all
- The ideal level of the characteristic might differ depending on environmental
conditions that change from one time and place to another. The average level of a
trait would gradually shift up or down within a given population in response to the
features of its current environment.
• Frequency dependent selection:
- We see a rough balance in the population between people who have a higher and
lower level of the characteristic. Green bird, blue bird example page 147.
- The frequency dependence will prevent the levels of a trait from becoming
extremely high or extremely low within a given society.
Review Table 7-1 page 148.
• Evolution / Sexuality
- men rank phys attractiveness more imp than wom (diffenrece = .54)
- women rank socio-econ stat & ambition more imp than man (diffeence= 0.68)
- willingness to have sex increases w length of relationship for men and wom
- but, knowing someone for 1 hr
. desire to have sex for men d=1.21 than wom
o The Evolutionary Explanation
- Men and women differ in minimal parental investment.
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