Which evolutionary mechanism is most likely to introduce new alleles into a population?

The introduction of new alleles into a population is primarily achieved through the process of mutation. Mutations are random changes in the genetic material of an organism, which can occur due to various factors such as environmental influences, errors during DNA replication, or through exposure to certain chemicals. These changes can lead to the creation of new alleles, which can then be inherited by subsequent generations if they occur in the germline (the reproductive cells).

Mutations play a critical role in the genetic variability of populations. Without mutations, all genetic diversity would eventually be lost due to factors like genetic drift or selective pressures. Additionally, while gene flow (the transfer of alleles between populations) can introduce existing alleles from one population to another, it does not create new alleles. Natural selection acts on the existing variation within a population, selecting for or against alleles based on fitness, but it does not create new genetic variation either. Genetic drift involves random fluctuations in allele frequencies, which can lead to the loss of alleles rather than introducing new ones.

Therefore, mutation stands out as the primary evolutionary mechanism responsible for introducing new alleles into populations, ensuring a continuous source of genetic diversity that is essential for evolution.