When my son was born, he was early and had a bit of a rough start, so his left hand got a bunch of oxygen and hearth sensors attached. To make sure they stayed there, the nurses taped his left hand to his breast.

After a few days, the hand was liberated, and he was completely surprised he had two of those hand things! He spent a long time just moving first his right hand, and then his left hand, symmetrically. Experimenting.

That convinced me how configurable humans are and from how far we come when born. We dont know we should have 2 hands, and an extra hand popping up from nowhere is no problem.