Final answer:
Genetic drift, gene flow, mutation, and natural selection are the factors that act to change allele frequencies and cause contemporary evolution in humans.
Step-by-step explanation:
The factors that act to change allele frequencies and cause contemporary evolution in humans are genetic drift, gene flow, mutation, and natural selection. Genetic drift refers to random changes in allele frequencies due to chance events, such as the founder effect or bottleneck effect. Gene flow is the movement of genes from one population to another through migration or the exchange of individuals. Mutation introduces new alleles into a population, while natural selection selects for alleles that provide a survival or reproductive advantage.