In sexually reproducing species, what is necessary for members of the same species?

In sexually reproducing species, for individuals to be classified as members of the same species, it is essential that they can produce both viable and fertile offspring. This criterion is known as the biological species concept, which emphasizes reproductive capability as a defining feature of a species. When organisms can mate and result in offspring that survive and can also reproduce, it demonstrates a genetic compatibility and allows for the continuation of the species’ genetic traits across generations.

Sharing a habitat, exhibiting similar behaviors, or having identical genomes might support the idea of being part of the same species but do not define it. These factors could vary significantly even among individuals of the same species without preventing successful reproduction. Thus, the ability to produce viable and fertile offspring is the primary and most crucial characteristic that solidifies the classification of organisms as belonging to the same species.