What is the evolutionary process by which new biological species arise?

The evolutionary process by which new biological species arise is known as speciation. This concept refers to the mechanisms through which populations evolve to become distinct species over time, typically through the accumulation of genetic differences. Speciation often occurs when populations become isolated from each other—either geographically (allopatric speciation) or reproductively (sympatric speciation)—reducing or eliminating gene flow between them. As these populations adapt to their specific environments and undergo natural selection, genetic divergence increases, leading to the emergence of new species.

In contrast, adaptation refers specifically to how organisms adjust to their environments through changes in traits over generations, but does not directly lead to the formation of new species. Diversification implies an increase in the number of different forms or species, but it is more of a broad term that doesn't specify the mechanisms involved in species formation. Isolation can lead to speciation, but it alone does not encompass the entire process of how new species are formed. Therefore, speciation is the most accurate term to describe the entire process involved in the emergence of distinct biological species.