Which of the following defines a species?

The definition of a species hinges on the ability of organisms to reproduce and produce fertile offspring, which is encapsulated in the second option. This concept, often referred to as the Biological Species Concept, emphasizes that members of the same species share a gene pool and are capable of interbreeding under natural conditions. The offspring resulting from such breeding must also be able to reproduce, ensuring the continuity of genetic traits within the species.

The other options do not adequately define a species. While some organisms may inhabit multiple environments, this adaptability does not necessarily correspond to being part of the same species. Additionally, organisms sharing a geographical location can belong to different species, particularly in areas where diverse species coexist. Lastly, identical physical characteristics may indicate members of the same species, but these characteristics alone can be misleading, as they don’t account for genetic diversity and reproductive capabilities. Thus, the ability to produce viable, fertile offspring truly encapsulates the essence of what defines a species in biological terms.