an example of natural selection the premises 1. phenotypic variation in a population. 2. phenotypic...
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An example of natural selection
• The premises• 1. Phenotypic variation in a population.• 2. Phenotypic variation has a genetic component• 3. Differential reproductive success
• Survival and reproduction is, on-average, nonrandom• 4. Phenotypic variation shifts between
generations in response to a changing environment.
Medium ground finchGeospiza fortisgeneration time: 4.5 yearslife span c. 16 years
120 mN = c. 1,200
Research of Peter and Rosemary Grant: 1973 - present
Hot spot
7 cm/yr
4-5 my
2-3 my
1 my
Adaptive radiationGalapagos finches
1: Is the population phenotypically variable?
Geospiza fortis
2: Is the variation heritable?(heritability: proportion of phenotypic variation due to genetic variation; c. 65%)
Evolution!
1977: drought130 to 24 mm precipitation A natural selector
Was there differential survival?
Effect of naturalselection
1.
2.
3.
The interplay
Seed abundance
Number of finches
Seed characteristicsof surviving plants
Had evolution taken place? Significant difference in beak size.
Note: naturalselection is alwaysone generationbehind theexpression of modifiedphenotypes
Natural selection cannot anticipate future “needs” of a population
• Evolutionary changes is based selection in the previous generation.
• 1. Parental population + environment (natural selectors)
• 2. Part of population selected to reproduce• 3. Transmission of heritable characteristics to the
new generation (e.g., size of the beak).– But the change was based on phenotypic variation among
their parents.
: species originate by divergence from common ancestors
Cladistic evolution vs. anagenesis or phyletic evolution
Darwin’s 1859 illustration (On the Origin of Species by Means of Natural Selection)