[wdfx]

I somewhat agree, but to me the semantics using unknown makes more sense as the function is attempting to answer a question of the input object.

"What is object? I don't know. Does it meet these conditions? Yes then object is Human else not."

[Etheryte]

While I see where you're coming from, semantic formulation like this is highly subjective. All the same the problem statement could be "Given any kind of input, tell me whether it's a Human or not".