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Misconception about NS
- - NS favors the survival of the species
- - behavior is based on either nature or nuture
- - culture triumps biology (or vice versa)
- - evolution is progressive
- - a biological explanation for a behavior that implies that is is justified
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what is Evolution?
- - change over time
- - in allele frequencies of a population from one generation to the next
- Evolution:
- Evolution allows us to explain relationships between living things. These resemblances are due to common descent from a shared ancestor.
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Natural Selection
- 1. Tendency to overpopulate
- 2. Individuals vary
- 3. Variation passed onto offspring
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Postulate #1 Overpopulation
- The ability of a population to expand is infinite, but the ability of an environment to support a population is always finite
- Environment Constraints Population Growth:
- ex. The Galapagos drought of 78'.
- The drought affected seed availability (large, tuff).
- Birds with beaks large enough to eat the seeds were most likely to survive.
- Variation:
- Organism's within populations vary, and this variation effects ability of organisms to survive and reproduce.
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Postulate #2 Variation
- Individuals vary in ability to survive and reproduce
- -beak size varied
- -small beak birds were less efficient at eating the seeds
- -larger beak depth in birds were more likely to survive
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Postulate #3 Inheritance
- Variations are transmitted from parents to offspring
- (beak size too?)
- characteristics of population changed over time
- -large beaked adults survived better
- -large beaked birds had large beaked offspring
- -mean beak size increased in population
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More on NS
- The three conditions (Darwins Postulates in conjunction with the Galapagos drought) produce competition between organism for sutvival.
- Organisms with advantageous raits pass them on
- -adaptations
- Leads to changes in a population
- NS acts on Variation
- -frequency of an allele will become more or less prevelant relative to other forms of the gene (pepper moth).
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