“What this shows is that for the nervous system to maintain uncrossed connections, the brain would need to keep flipping one axis of its body maps as the body parts moved, which would be impossibly complex.”
Every bilateral animal down to the nematode wires the left body to the right brain. Troy Shinbrot and Wise Young at Rutgers argue it is the topologically simplest way to map a 3D body onto a folded cortex. The answer comes from geometry, not biology, and there is very little biological research testing it. Every doctor relies on the crossover in a neurological exam and still answers “why” with a shrug.