The axolotl is a salamander that refuses to become an adult, staying in a permanent larval state and breeding that way — and in that frozen-youth body hides the most spectacular regenerative power of any vertebrate. Scientists have spent decades trying to steal its secret for human medicine. Meanwhile the wild population, confined to the dying canals of Mexico City, is collapsing toward extinction.
Start here: the biology of neoteny, where an animal reaches sexual maturity while keeping its juvenile body — gills, tail fin, and all — never undergoing the metamorphosis that turns other salamanders into land dwellers.
National Geographic's primer on the animal behind a thousand memes — the permanent smile, the frilly external gills, and the strange fact that a creature so beloved online is barely hanging on in the wild.
The Marine Biological Laboratory — one of the world's great centers for regeneration research — shows how and why the axolotl can rebuild lost body parts, and what that could eventually mean for human medicine.
The hard list of what it can actually do: limbs, heart tissue, spinal cord, and sections of brain — all without forming scar tissue. Cells at the wound edge revert to an embryonic state and build the missing part from scratch.
Time-lapse footage from the Institute of Molecular Biotechnology showing an axolotl limb regrowing — the closest thing biology has to watching a body print a replacement part in real time.
BBC's look at the axolotl's home in the ancient canals of Xochimilco, and the centuries-old relationship between the animal, Aztec mythology (it was named for a god who refused to die), and the people trying to save it today.
The cruel paradox: an animal that can regrow its own brain cannot survive the pollution, draining, and invasive fish that have reduced its only wild home to a few scattered canals, with population counts crashing toward zero.