New research conducted by Denis Duboule and colleagues at the University of Geneva published in the Jan. 21, 2014, issue of the journal Public Library of Science Biology has shown that the genetic structures that form fins in fish and limbs in animals existed in an unknown ancestor of both species.
The same gene groups are found in fish and four-footed mammals. These same gene groups produce the development of fins in fish and four limbs in mammals. The two gene sets have been found in the oldest known ancestor of mammals that is thought to have been the first fish to venture out onto land about 350 million years ago.
The researchers found that the two gene groups are not active in both species of animals but the main genetic mechanism used to pattern tetrapod limbs was already present in fish.
The researchers are the first to discover that the gene group that is responsible for the formation of digits (fingers and toes) in mammals does exist in fish but is not expressed or activated in fish. The spiny portion of fish fins cannot be deemed equivalent to digits in mammals.
At some time in the unknown past a creature that is not known developed the genetic capacity to produce both fins and limbs. Over time the differentiation of genetic initiators made the distinction between the development of fins in fish and the development of limbs and digits in mammals possible.