Factors Affecting Evolution
Natural Selection
Variation in a species leads to some individuals being more well-suited to the
environment than others
These individuals are more likely to survive and reproduce to pass on their
advantageous alleles
This affects the allele frequency
Stabilizing Selection:
o Occurs when the environment remains unchanging
o Reduces genetic variation in the population
o Favours an intermediate allele
Directional Selection:
o Occurs when there is a change to the environment
o Gradual shift in the optimum value for the trait
o Favours an extreme allele
Disruptive/Diversifying Selection:
o Favours both extreme alleles
o Favours against the intermediate allele
Natural Selection
Variation in a species leads to some individuals being more well-suited to the
environment than others
These individuals are more likely to survive and reproduce to pass on their
advantageous alleles
This affects the allele frequency
Stabilizing Selection:
o Occurs when the environment remains unchanging
o Reduces genetic variation in the population
o Favours an intermediate allele
Directional Selection:
o Occurs when there is a change to the environment
o Gradual shift in the optimum value for the trait
o Favours an extreme allele
Disruptive/Diversifying Selection:
o Favours both extreme alleles
o Favours against the intermediate allele
