The Evolution of Regeneration in Salamanders
Amphibians evolved from fish and their limbs grew out of the fins of the fish. The pelvic fins formed the hind legs and the pectoral fins formed the forelimbs.
The Coelocanth (Latimeria crossopterygi):an ancestral fish dating back 75 million years. thought to be extinct unitl caught off the coast of Africa in 1938.
Notice the beginning of limb formation from the fins (Dorcas, lecture 10/17/00, <http://www.bio.davidson.edu/biology/midorcas/animalphysiology/Lectures/2000/index.htm>)
It has been proposed that the homeotic transformation in the expression of a Hox gene accounted for the evolutionary transition. Some fish have the ability to regenerate fins, and more importantly, amputated fins respond the same way to retonic acid, a molecular signal in regeneration, as amphibian limbs. This suggests that both limb structures have common mechanisms that were preserved during evolution and supports the theory that regeneration has a developmental and evolutionary origin as opposed to adaptive (14).