Introduction to Evolution

Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals
Natural selection increases the match between organisms and their environment over time
If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species
* Note that individuals do not evolve; populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
Adaptations vary with different environments
Why natural selection can’t fashion perfect organisms:
  * Selection can act only on existing variations
  * Evolution is limited by historical constraints
  * Adaptations are often compromises
  * Chance, natural selection, and the environment interact

Homology: similarity resulting from common ancestry and is the result of divergent evolution.
Homologous structures: anatomical resemblances that represent variations on a structural theme present in a common ancestor
Convergent evolution: the evolution of similar, or analogous, features in distantly related groups
* Convergent evolution does not provide information about ancestry
Analogous traits arise when groups independently adapt to similar environments in similar ways
Homologous genes: two genes derived from the same ancestral gene
* Orthologs occur in separate species
Molecular processes reveals molecular details of evolutionary change
Two sequences may be similar, but not identical due to the independent accumulation of different random mutations