According to the biological definition of species, which organisms belong to the same species?

The biological definition of species is primarily focused on the ability of organisms to interbreed and produce fertile offspring. This concept is crucial because it emphasizes reproductive isolation, meaning that members of the same species are capable of mating with each other under natural conditions, resulting in offspring that are not only viable but also capable of reproducing themselves.

When two organisms can produce fertile offspring, it indicates a shared gene pool, which is essential for maintaining the genetic continuity of a species. This reproductive ability can help prevent inter-species breeding, which could lead to a breakdown of species integrity over generations.

In contrast, while sharing a common habitat may bring organisms into contact, it does not define them as a single species, as different species can coexist in the same environment. The suggestion that organisms can interbreed with any other organism is incorrect because it overlooks the concept of reproductive barriers that often exist between different species. Lastly, while similar DNA sequences can indicate a close relationship, they do not guarantee that these organisms can interbreed. DNA comparison alone is insufficient for defining species without considering reproductive capabilities.