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Key Points About Natural Selection
1) Natural selection operates within generations; evolution
occurs between generations
2) Natural selection alters the properties of populations.
3) Natural selection is not forward thinking or directed in
purpose.
3) Natural selection does not exist for the good of a species.
Why Evolution by Natural Selection Works
Individuals of populations exhibit genetically
based variation in traits that affect survival and
reproduction.
NS and HIV
Phenotypic Variation
|-- Drought --|
|-- Drought --|
Hatchlings (1976)
Hatchlings (1978)
Evolution
Occurs
Between
Generations
Heritability of Beak Depth in Medium Ground Finches
Adaptation
ForagingCompetition
Hypothesis
Evolution is more than armchair science:
hypotheses must be tested
Prediction: If necks evolved for the purpose of foraging at the
tops of trees, that’s where they should preferentially forage.
Even during
drought
conditions
Alternative Hypothesis: Necks are used
as a weapon. Simmons and Scheepers 1996
Pratt and
Anderson 1985
Things to keep in mind when
studying adaptation
• Differences among individuals are
not always adaptive
• Not every trait is an adaptation
• Not every adaptation is perfect
Tephritid flies: Do they mimic jumping
spiders to escape predation?
Phidippus
Zonosemata
Hypothesis 1: No mimicry
Hypothesis 2: Mimicry deters other predators
Hypothesis 3: Mimicry deters jumping spiders
20 spiders tested for each treatment
Jumping spiders
retreated
Jumping spiders
munched