A creature that does not scar
Cut off an axolotl's leg and it grows back. Not approximately, the bone, muscle, nerves, and skin return in the correct arrangement, fully functional, within weeks. The same happens with its heart muscle after damage, with segments of its spinal cord after injury, and with portions of its brain. No other vertebrate on Earth does this across so many tissue types. The axolotl (Ambystoma mexicanum), a freshwater salamander native to the lake system around Mexico City, has been a laboratory subject since the 1860s, but the molecular detail of how its regeneration actually works has only become legible in the last two decades, as gene sequencing tools caught up with the biology.
