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)