Evidence of Evolution
Chapter 8
Historical
• Jean-Baptiste Lamarck
Alfred Wallace
Voyage of the Beagle
Darwin and Natural Selection
A Key Insight – Variation in Traits
 Darwin’s observations:
• Populations can produce more individuals than
their environment can support
• Some versions of a trait might enhance an
individual’s ability to survive and reproduce in its
environment
Finches in the Galapagos Islands
Terms
 Alleles
• Heterozygote
• homozygote




Genotype
Phenotype
Frequency
equilibrium
genotype
phenotype
At What Level Does Evolution Occur?
 Individuals don’t evolve, populations do!
490 AA butterflies
dark-blue wings
490 AA butterflies
dark-blue wings
490 AA butterflies
dark-blue wings
420 Aa butterflies
medium-blue wings
420 Aa butterflies
medium-blue wings
420 Aa butterflies
medium-blue wings
90 aa butterflies
white wings
90 aa butterflies
white wings
90 aa butterflies
white wings
Starting Population
Next Generation
Next Generation
Fig. 18-3b, p. 280
How can a gene pool change?
• Mutation
• Genetic drift
• Gene flow
(migration)
• Natural selection
• Sexual selection
• Will the above have
more of an effect on
a large population or
a small population?
Why?
Genetic Drift—
The Chance Changes
 Genetic drift
• A random change in allele frequencies over time
• Founder effect
• Bottleneck Effect
Genetic drift is pronounced when a few
individuals start a new population
Gene Flow (Migration)
Natural Selection
 Differential survival and reproduction among
individuals of a population that vary in the details
of their shared traits
 In other words….. Some organisms have a
better chance of surviving and reproducing than
other organisms depending on their traits
Natural Selection
Natural selection
 Differential survival and reproduction
among individuals of a population that
vary in details of shared, inherited traits
Adaptive trait
 Any trait that enhances
an individual’s fitnessability to survive and reproduce in a
particular environment)
Not this
kind of
fitness!
Sexual Selection
 With sexual selection, some version of a trait
gives an individual an advantage over others in
attracting mates
Sexual Selection