How does natural selection contribute to the formation of new species?

Natural selection contributes to the formation of new species primarily by driving the genetic divergence that leads to reproductive isolation. This process generally occurs in two ways:1

• Incidental Divergence: As populations adapt to different environments, their gene pools accumulate distinct changes. Over time, these populations may become so genetically different that they can no longer interbreed, effectively splitting the original lineage.21
• Direct Promotion of Isolation: When hybrid offspring between two diverging populations have reduced fitness, natural selection directly favors the development of reproductive isolating mechanisms (RIMs). By selecting against hybridization, the process reinforces the separation of the two groups, eventually establishing them as distinct species.1

Ultimately, speciation is the result of a gene pool breaking into isolated units. Whether through geographic barriers or ecological shifts, natural selection ensures that populations adapt to their specific conditions, preserving the evolutionary history of the lineage while fostering the diversity of life.34