How Some Animals Regrow Limbs — and Even Whole Bodies

Scientists ran an experiment with a freshwater animal called the hydra. They ground the animals in a porcelain mortar and stirred the resulting paste into water. After a while, new hydras started growing from the crushed particles. Every microscopic fragment of the mass produced a new polyp.

Here’s another striking example: if you cut off a starfish’s arm, the animal can grow a new one. If you cut a starfish into, say, five pieces and put them into seawater, each fragment can develop into a whole new starfish.

Regeneration appears in more complex animals too. For example, some lizards can drop their tails when a predator grabs them. Over time a new tail grows back, although it may be shorter or stubbier than the original.