Final answer:
Gene flow contributes to genetic diversity and heterogeneity within a species. However, if populations become isolated, this lack of gene flow can lead to divergence and potentially allopatric speciation over time as evolutionary forces act independently on each population.
Step-by-step explanation:
Lack of Gene Flow Leads to Divergence:
Gene flow is a crucial evolutionary process involving the transfer of genes between populations, promoting genetic diversity. When populations are geographically separated, this gene flow is restricted, which can lead to genetic divergence over time as new alleles arise through mutation. This process can eventually result in allopatric speciation, whereby two populations evolve to become distinct species. The isolation can be due to natural barriers such as the formation of a lake or river, or through mechanisms like seeds being dispersed to an isolated location like an island.
As an example, if a new lake divides two rodent populations, continued gene flow would be unlikely, making speciation a more probable outcome. This isolation allows populations to adapt to their local environment and accumulate genetic differences that contribute to speciation. The divergence can also be accelerated by natural selection, genetic drift, and the specific environmental conditions each separated population faces.
Moreover, prolonged isolation can have negative implications, such as an increase in the frequency of deleterious alleles within a population, which can lead to genetic disorders, as seen in culturally isolated human populations practicing endogamy.