Final answer:
Option (D), The best piece of evidence supporting the hypothesis that modern humans and Neanderthals are separate species is DNA analysis revealing distinct genetic lineages, despite some instances of interbreeding.
Step-by-step explanation:
The question asks which piece of evidence best supports the hypothesis that modern humans and Neanderthals are separate species. The correct answer is D) DNA analysis revealing distinct genetic lineages. Although there is evidence of interbreeding, as modern European and Middle Eastern populations have between 1 and 4 percent Neanderthal DNA, this interbreeding does not preclude them from being separate species. It's important to note that the sharing of some genetic material does not necessarily mean two groups are the same species.
Further genetic studies have shown that while there was some interbreeding, Neanderthals and modern humans are more closely related to each other than either is to the Denisovans, suggesting separate evolutionary paths. Concurrently, Neanderthals, Denisovans, and modern humans share a common but distant ancestor, likely Homo heidelbergensis. The genetic evidence points towards significant divergences in the evolutionary lineages of modern humans and Neanderthals, suggesting they are indeed separate species, despite some genetic admixture.