Which statement is true about species?

The statement about species that is true is that all members of a species can produce fertile offspring. This concept is a fundamental aspect of the biological species definition, which emphasizes reproductive isolation and the ability to produce viable offspring. When organisms belong to the same species, they share genetic similarities that enable them to mate and produce offspring that can also reproduce. This reproductive capability is a key criterion for defining what constitutes a species, allowing for the maintenance of a distinct gene pool.

The other options do not hold true under scrutiny. For instance, not all members of the same species are visually identical due to variations in phenotypes caused by genetic and environmental factors. Additionally, while classification of species can sometimes be challenging due to the presence of hybrid species and varying definitions, they are not always easily categorized into clear categories. Finally, species are not necessarily geographically isolated; many species inhabit overlapping regions and can come into contact with other species without being separated by geographical barriers.