If you’ve ever chased a lizard or watched it run away from something, you might have noticed it drop its tail and run away. In a few weeks, it may grow back its tail. Lizards have the remarkable ability to grow back an entire limb!Â
Lizards are not the only organisms to regrow limbs. Across the animal kingdom – from cockroaches to crickets, axolotls to anemones, regeneration is possible.
Regeneration is essentially superpowered healing. It is the process of restoring tissues, limbs, and organs to a state that mimics the original. Healing cannot replace the original and is marked by scars and a loss of function. In other words, regeneration is like the original document and healing is like a badly scanned copy.
Stem Cells are the key to regeneration. The cells that make up our hair, skin, liver, heart, and every other part of our body are as different as the final tissues are. These are specialized cells. Hair and skin grow back when these specialized cells divide, but hair can’t turn into skin, and bones can’t turn into muscle cells. Stem cells are entirely undifferentiated cells, which have the potential to become anything! Embryos are made mostly of stem cells, though as the embryo develops the number of stem cells dwindle.  As adults, the only stem cells we have lie within our bone marrow, but even these are partially specialized to give rise to the cells that make up our blood.