The process of one species evolving into two or more species is called speciation. This occurs when populations of a species become geographically or reproductively isolated, leading to divergent evolutionary paths. Over time, genetic differences accumulate due to natural selection, genetic drift, and other evolutionary forces. Eventually, these changes result in the emergence of distinct species that can no longer interbreed. Speciation is a fundamental concept in evolutionary biology, illustrating the dynamic nature of life on Earth.