The right option is; Genetic drift
Modern travel along with migration reduces the probability of genetic drift having an effect on the evolution of humans.
Genetic drift is a process of evolution in which an existing gene variant of a population changes over generations due to random sampling of organisms. Genetic drift usually occurs in smaller populations of organisms. The gene variant (allele) may increase or decrease in a population and when the gene variant is not responsible for the change in the rate of its occurrence in a population, genetic drift is acting on the gene variant.