Answer:
The correct answer would be - biological species concept.
Explanation:
The biological species concept is a concept of speciation or how a species forms in nature. According to this, a species is the group of the population that can naturally or potentially interbreed with each other, not on the basis of their physical similarities or habitats.
The physical appearance could be useful as recognizing a species but not defining it. As neanderthals show very little or no gene flow with a modern human it means they do not belong to the same species as modern homo sapiens.
Thus, the correct answer is- biological species concept.
