several individuals are entering a new population
natural selection gene flow genetic drift
The scenario you described, where several individuals are entering a new population, is primarily associated with gene flow.
Gene flow refers to the transfer of genetic material (alleles) between populations through the movement of individuals or their gametes (e.g., pollen). When individuals from one population migrate to another and breed, they introduce new alleles into the gene pool of the receiving population, which can affect its genetic diversity and evolutionary trajectory.
In contrast:
Natural selection is the process by which certain traits become more or less common in a population due to the differential survival and reproduction of individuals based on those traits. It does not directly involve the movement of individuals between populations.
Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies in a population, particularly in small populations. It is not directly related to the movement of individuals between populations but rather to random sampling effects.
So, in the context of your question, the correct answer is **gene