Final answer:
True, some populations considered separate species can interbreed and produce fertile offspring, especially in areas known as hybrid zones where the viability of hybrids can influence the determination of species separation.
Step-by-step explanation:
The statement that some populations that are considered to be separate species can interbreed and produce fertile offspring is true to an extent. In biology, a species is generally defined as a group of individual organisms that can interbreed with one another and produce fertile, viable offspring. However, there are exceptions where two separate species may produce offspring in an area known as the hybrid zone. The viability of these hybrids can impact whether or not these populations are considered separate species.
For example, if hybrid offspring are more fit than their parents, reproduction between both species and the hybrids might continue, potentially leading to a merge under the umbrella of one species. This would mean that the original populations are not reproductively isolated. Also, if hybrid zones exist and the hybrids are both viable and successful, it indicates that the two populations are not yet fully reproductively isolated.