The separation of a population of organisms from exchanging genetic material with other organisms of the same species due to physical barriers constitutes a significant evolutionary force. This separation, often brought about by landforms such as mountains, bodies of water, or expansive deserts, prevents interbreeding and gene flow between the isolated groups. As a result, the isolated populations experience independent evolutionary trajectories, potentially leading to the accumulation of distinct genetic differences over time. A classic example is the divergence of species on either side of a mountain range, where limited or no migration can occur.
This form of reproductive isolation is a cornerstone of speciation, the process by which new species arise. By impeding gene flow, it allows natural selection, genetic drift, and mutation to act independently on each population. This independent evolution can result in the development of unique adaptations tailored to the specific environments inhabited by each group. The accumulation of these differences may eventually render the populations reproductively incompatible, even if the physical barrier is later removed. The historical context of this phenomenon is deeply intertwined with Darwin’s observations on the Galapagos Islands, which provided key insights into the role of isolation in the diversification of life.
