Final answer:
Natural selection contributes to genetic variation between groups by selecting for beneficial alleles and behaviors, and reducing the frequency of deleterious alleles.
Step-by-step explanation:
Natural selection acts on the population's heritable traits: selecting for beneficial alleles that allow for environmental adaptation, and thus increasing their frequency in the population, while selecting against deleterious alleles and thereby decreasing their frequency. Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities.
Genetic drift stems from the chance occurrence that some individuals in the gene line have more offspring than others. When individuals leave or join the population, allele frequencies can change as a result of gene flow. Mutations to an individual's DNA may introduce new variation into a population.
In summary, natural selection contributes to some of the genetic variation between groups by favoring beneficial alleles and behaviors, and reducing the frequency of deleterious alleles.