### African Spiny Mouse
Acomys cahirinus
This tiny mammal can perfectly regrow massive chunks of missing skin, muscle, and cartilage without leaving a single scar.
The Story
Mammals are notoriously terrible at regenerating. When humans suffer a deep cut, our bodies panic and quickly plug the hole with thick, stiff scar tissue. But the African spiny mouse (Acomys cahirinus) completely ignores the mammalian rulebook. It is the only known mammal that can heal devastating injuries with perfectly fresh tissue, leaving absolutely no scar behind.
How powerful is this mouse's healing factor? Scientists tested it by punching a massive four-millimeter hole straight through the mouse's ear. Instead of forming a permanent gap or a tough lump of scar tissue, the ear completely closed up with brand-new skin, hair, and cartilage.
Even more jaw-dropping is what happens if it suffers a completely severed spinal cord. While this catastrophic injury causes permanent paralysis in almost any other mammal, the African spiny mouse can recover up to 60 percent of its motor function and regain full bladder control within just 60 days.
How It Works
- Blastema Building: Instead of rushing to build a fibrous scar, the mouse mounts a localized inflammatory response packed with Reactive Oxygen Species (ROS). This triggers the rapid growth of a "blastema"—a mass of flexible, stem-cell-like tissue normally only seen in regenerating amphibians. - Perfect Rebuilding: From that blastema, the mouse doesn't just patch the skin. It regrows functional hair follicles, sebaceous glands, cartilage, and even entirely new skeletal muscle by generating embryonic myosin (the exact same proteins used to build muscle before it was born).
