“In our own bodies, only the liver is capable of limited regeneration, but chop a limb off a starfish or a salamander, and it will grow a new one. We are starting to understand the molecular signals that are used by these species to regenerate limbs in adult life. Mammals seem to only use this signalling pathway during the growth of the early embryo but it is a pathway that may well have the potential to be reactivated. Following surgical removal, the wings can grow back in embryonic chickens when the production of a protein called wnt is switched on. Frog limb regeneration can also take place later in the life cycle when wnt protein is expressed. Tadpoles have this ability but it is normally lost when they metamorphose into frogs. The expression of wnt signalling protein around an injury is thought to cause a reprogramming or transdifferentiation of mature cells into stem cells capable of producing the cell types needed for the limb. Very young children have been known to re-grow severed fingertips, and so there are intriguing possibilities for human tissue regeneration.”