Which mechanism is the main source of new genetic variation within a population?

Mutation is the primary source of new genetic variation within a population because it introduces new alleles into the gene pool. Mutations can occur in various ways, such as through copying errors during DNA replication, environmental factors, or chemical exposures. These changes in the genetic code can result in new traits that may not have previously existed within the population, contributing to the genetic diversity necessary for evolution.

Without mutation, a population would eventually reach a genetic equilibrium, limiting the potential for evolution and adaptation to changing environments. While mechanisms like natural selection, gene flow, and genetic drift play important roles in shaping populations and affecting allele frequencies, they do not create new genetic variation; rather, they act on the variation already present within the population. Thus, mutation stands out as the unique driver of new genetic diversity.