If we did that, would we be really replicating what nature does, or would we be just simulating it?

Human intelligence and consciousness are embodied. They are emerging features of complex biological systems that evolved over thousands and millions of years. The desirable intelligent behaviours that we seek to replicate are exhibited by those same biological systems only after decades of growth and training.

We can only hope to simulate these processes, not replicate them exactly. And the problem with such a simulation is that we have no idea if the stuff that we are necessarily leaving out is actually essential to the outcome that we seek.