No, generally within science 'species' has a loose definition that roughly correlates with the actual underlying physical events occurring in the wild (the true population of the gene pool).

For example, if pressed, about as much as you could get from an evo biologist is that what distinguishes difference between species is their inability to interbreed.

Humans probably could tell neanderthal were "different" but not in a way where they thought they were truly "other".