Final answer:
Speciation on a genetic level between two isolated populations occurs due to genetic drift, natural selection, mutation, and gene flow. Mutation and gene flow are key in introducing new genetic variations, while genetic drift and natural selection can change allele frequencies, leading to speciation.
Step-by-step explanation:
Speciation generally starts on a genetic level between two isolated populations through several processes that introduce new genetic variation or change allele frequencies. These processes include genetic drift, natural selection, mutation, and gene flow. Among these, mutation and gene flow are the primary forces that introduce new genetic variations into a population.
Mutations, which are changes to an organism's DNA, can lead to the emergence of new alleles and are important in generating diversity within a population. On the other hand, gene flow refers to the transfer of alleles from one population to another, typically through migration, increasing variation within the recipient population. Natural selection can act on these variations, leading to differential reproductive success based on the adaptive value of the traits. Genetic drift, which is the random fluctuation of allele frequencies, can cause certain alleles to become more or less common simply by chance.
When considering allopatric speciation, the separation of populations by a physical barrier like distance can quicken speciation by limiting gene flow between them. In the absence of gene flow, genetic drift and mutation can lead to divergence between populations. Natural selection will also act differently on each population based on their specific environments, leading to adaptive differences that contribute to speciation.