If you look at research into the fundamental biological mechanisms of healing, you'll quickly see that we mammals are not optimally evolved. There are all sorts of changes and tweaks that may allow far greater regeneration in specific circumstances, such as nerve injury. Here is one example: "Scars can serve as double-edged swords in spinal cord injuries ... The scar forms a wall around the wound, preventing the injury from spreading, but [releases] molecules that keep severed nerve fibers from passing the damaged tissue, so they cannot connect with their original targets to restore motor and sensory function. ... [researchers have] identified where these potent molecules - called chondroitin sulfate proteoglycans (CSPGs) - bind to the surface of neurons, exposing a novel therapeutic target. ... This discovery suggests that we might be able to treat central nervous system injuries with a pill in the future ... It's hard to overcome CSPGs in the human body, but receptors may offer an easier target ... follow-up experiments in culture dishes on neurons missing the receptor - called PTP sigma - and studies in mice confirmed the connection. ... [researchers] observed unprecedented levels of growth in the neurons of injured mice missing the PTP sigma receptor. In fact, motor neurons sent extensions all the way through the scar and well beyond the wound."