though symmetry in the human body disappears when there is no adaptive pressure to retain it
In my view, this statement puts things upside-down: If you consider evolution of organisms, the more primitive was the more symmetrical, and each breach of symmetry represented a jump in evolution (spherical -> cylindrical -> flat with differentiated underside -> front-end and back end + left and right asymmetry). It was thus "adaptive pressure" that made asymmetrical organisms "win", roughly speaking. There are still highly symmetrical competitors around, like the viruses (do not re-start a thread about this plural).