"Is it possible to define a human being without any any metaphysical hypothesis?"
Some (Proponents of scientism) might strongly disagree with what I am about to say, but I will support my claims in the upcoming paragraphs.
Yes, It is impossible to Define a human being without any metaphysical postulation.
Let me explain: In general, when we say "define" X, for the lack of a better name, we intend to ask what does it mean to be X. Whoops, did we just tread into ontology?
Since the very question is ontological, its answer would, by definition (pun intended), be metaphysical. "Why is that," you ask? Because ontology is a subset of metaphysics. Let us take a tangible example; let us define a car. "What is a car," can be equivalently paraphrased into "what does it mean to be a car." It should be quite clear after the paraphrase, that the question is asking nothing but what are the "essential" attributes instantiated by a car.
That said, essentialism is not needed. I just used it to give you an example. There are two broad catagories of theories dominating contemporary ontology: Nominalism, and Ontological realism. Both of these catagories have numerous particular theories within.
However, one thing we can be certain of: the answer to the question "Define X," is necessarily metaphysical.
I hope that answers your question.