Download Natural Selection

Natural Selection
Darwin vs Lamarck
• Lamarck - animals pa on acquired traits
• Darwin - individuals are selected for
survival by combinations of traits
• see page 303
Darwin...
• More individuals are born than live to
reproduce
• individuals vary from one another
• individuals compete with each other for
resources
• individuals with the best combination of
traits for the given conditions will survive
What does natural selection not
account for?
Neo-Darwinism or Synthetic
theory of evolution
• Darwin posited that traits are passed on
directly to the next generation
• Mendel had already determined that traits
are passed along as a matter of chance
• the combination of Darwinian natural
selection and Mendelian genetics is called
the synthetic theory of evolution
Evidence of evolution
• Fossil record
• Comparative anatomy (see Figure 7-17 on
page 308)
• Biogeography
• subcellular
Is the fossil record a complete
record?
Comparative anatomy
• Homologous features- similar structure in
different species
• Analogous features - similar function
different structure (convergent evolution)
• Vestigial organs
Biogeography
• Evolution occurs only once
• Center of origin
• Related species have similar patterns of
development (figure 17-12, page 313)
Subcellular
• DNA is universal
• the longer the time since divergence the
greater the difference in DNA
Microevolution
• Population = gene pool
• Microevolution- small gradual changes
within a population over time. Accounts for
differences between population of same
species
Hardy-Weinberg Principle
• This never occurs in nature but helps to
understand the forces of evolution.
• The frequency of genotypes in a population
can be determined /described
mathematically
• Inheritance itself will not cause a
change in allele frequencies
Inheritance itself will not cause a
change in allele frequencies
• Allele frequencies will not occur if
•
•
•
•
•
there is random mating
there are no mutations
there is no migration
there is no natural selection
UNDER THESE CONDITIONS THERE IS
GENETIC EQUILIBRIUM!!!!
Mutation
• A random, permanent change in DNA
• does not determine the direction of
evolution (mutations occur randomly, not in
response to need or conditions)
• Genetic drift - (founder effect)
• Genetic bottleneck -
Selection
• Stabilizing selection - tends to make
population more uniform
• Directional stabilization - favors one
extreme
• Disruptive stabilization - favors both
extremes
• see page 327
Variation
• Genetic polymorphism - two or more alleles
for a given gene.
• What is the heterozygous advantage?
Speciation
• Species - members freely breed with one
another
• Reproductive isolation – temporal isolation (different times)
– behavioral isolation (courtship patterns)
– mechanical isolation
Speciation
• Allopatric speciation - geographic
separation results in new species
• sympatric speciation - divergence in same
geographic area (insects)