• Process in which individuals with certain inherited characteristics are more likely to survive in an environment, reproduce and pass on those traits → traits have selective advantage
    • Environment is the main force behind natural selection → controls which traits are most beneficial (Selective pressure)
  • Superior traits are adaptations to the environment and increase an individual’s fitness (relative ability to survive and leave offspring)
    • Environment favors a trait = trait increases individuals fitness → selection is said to act for that trait
      • Selection also acts against unfavorable traits

Observations for Evolution

  1. Populations possess enormous reproductive potential
  2. Resources are limited. resources don’t increase as populations do
  3. Individuals compete for survival. Overproduction = competition for available resources
  4. There is heritable variation among individuals in a population.
  • Genetic variation is the basis of phenotypic variation that can be acted upon by natural selection → evolution
  1. Only most fit individuals survive. “Survival of the fittest” occurs because individuals with traits adapted for survival and reproduction are able to out-compete other individuals for resources and mates
  2. Evolution occurs as favorable traits accumulate in the population. Results from the unequal ability of organisms to survive and reproduce
  • As the unsuccessful died off and the successful rises, the adaptations become common

Key Features of Natural Selection

  • Natural selection acts on phenotypic variation
  • Overtime can increase the frequency of desirable traits → adaptive evolution
  • If environment changes or individual moves → apply new selective pressures → the process may result in new adaptations & species
  • Individuals DO NOT evolve — populations do
  • Process of editing species, not creating
  • Evolution by natural selection can occur quickly in fast multiplying species bcuz mutations are common → produces genetic variation
  • Natural selection limited to modifying structures already present → not perfect
  • Evolution by natural selection is a blend of chance and “sorting”
    • Chance in the creation of new genetic variations (as in mutation) and sorting as natural selection favours some alleles over others.
    • Because of this favouring process, the outcome of natural selection is not random.