- 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
- Environment favors a trait = trait increases individuals fitness → selection is said to act for that trait
Observations for Evolution
- Populations possess enormous reproductive potential
- Resources are limited. resources don’t increase as populations do
- Individuals compete for survival. Overproduction = competition for available resources
- 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
- 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
- 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.