Variation in a trait is a required condition for natural selection to act on a population for that trait. Assuming a population of organisms started with only one form of trait, what are two ways variation in the trait could be introduced into the population?
One way of creating a variation in a population is through genetic replication errors. This will make a new type of alleles. Environmental factors cause variation such as affecting enzyme activity and function. The changes would show in the phenotype of an organism.