Defines species as interbreeding populations reproductively isolated from other such populations.

• A. Speciation
• B. Species
• C. Cladistics
• D. Biological species concept

Answer: (D)

The Biological Species Concept defines a species as a group of interbreeding natural populations that are reproductively isolated from other such groups. This emphasizes gene flow within the population and barriers to mating with others, which keeps separate lineages from exchanging genes. It explains why populations that could potentially mate are considered the same species only if they actually do so and share a common gene pool. This concept is widely used for sexually reproducing organisms, though it has limitations for asexual organisms and fossils where reproductive behavior can’t be observed. Other options don’t fit as a definition: speciation is the process by which new species arise; cladistics is a method for inferring evolutionary relationships based on shared traits; and simply “Species” is a taxonomic label, not a criterion for defining what constitutes a species.