What defines organisms that belong to the same species?

Organisms that belong to the same species are defined primarily by their ability to interbreed and produce fertile offspring. This biological concept emphasizes reproductive isolation from other groups, meaning that individuals of the same species can mate successfully under natural conditions, resulting in offspring that can also reproduce. This criterion is crucial because it encapsulates the genetic continuity and shared characteristics that define a species.

While a shared habitat, similar diets, or common physical features may describe groups of organisms that live in the same area or look alike, these factors do not accurately determine species boundaries. Different species can share habitats and diets and might even exhibit physical similarities, yet they remain distinct due to reproductive differences. Thus, the ability to interbreed effectively and produce viable offspring is the fundamental criterion that accurately defines what constitutes a species.