Positive vs Negative Allele Selection
There are two types of natural selection in biological evolution:
Positive selection promotes the spread of beneficial alleles, and negative selection hinders the spread of deleterious alleles
Positive selection is selection that favours a heritable trait and the allele for that trait will increase within a population.
Negative selection is selection that disfavours a heritable trait and the allele for that trait will decrease within a population.