Scientists believe they have discovered “evidence for a fundamental evolutionary link” between humans and fish in a gene that shares a name with a computer game hedgehog.

The idea that human limbs developed from fish gills was first proposed by German anatomist Karl Gegenbaur 138 years ago , but it was widely discredited due to lack of supporting fossil evidence

However, using the latest genetic techniques scientists have discovered similarities between the genetic mechanism that controls the development of the gill arches of skate fish and human limbs.

The gene in question is called the Sonic gene and was named after the videogame character by a research team at Harvard Medical School.

“The fact that the Sonic gene performs the same two functions in the development of gill arches in skate embryos as it does in the development of limbs in mammal embryos may help to explain how Gegenbaur arrived at his controversial theory on the origin of fins and limbs,” said lead researcher, Dr Andrew Gillis.

“Gegenbaur looked at the way that branchial rays connect to the gill arches and noticed that it looks very similar to the way that the fin and limb skeleton articulates with the shoulder,” said Gillis. “The branchial rays extend like a series of fingers down the side of a shark gill arch.”

In mammal embryos, the Sonic gene dictates the identity of each finger and maintains growth of the limb skeleton. “In a hand, for instance, Sonic tells the limb which side will be the thumb and which side will be the pinky finger,” explains Gillis.

To test whether the gene functions in the same way in skate embryos, Gillis and his colleagues inhibited Sonic at different points during their development.

They found that if Sonic was interrupted early in development, branchial rays formed on the wrong side of the gill arch, and if the Sonic gene was interrupted later in development, then fewer branchial rays formed but the ones that did grow, grew on the correct side of the gill arch.

These finding show that the gene works in a remarkably similar way in fish as it does in the development of human limbs.

“Taken to the extreme, these experiments could be interpreted as evidence that limbs share a genetic programme with gill arches because fins and limbs evolved by transformation of a gill arch in an ancestral vertebrate, as proposed by Gegenbaur,” says Gillis.

“However, it could also be that these structures evolved separately, but re-used the same pre-existing genetic programme. Without fossil evidence this remains a bit of a mystery (there is a gap in the fossil record between species with no fins and then suddenly species with paired fins) so we can’t really be sure yet how paired appendages evolved.”

“Either way this is a fascinating discovery, because it provides evidence for a fundamental evolutionary link between branchial rays and limbs,” said Gillis. “While palaeontologists look for fossils to try to reconstruct the evolutionary history of anatomy, we are effectively trying to reconstruct the evolutionary history of genetic programmes that control the development of anatomy.”

“What we are learning is that many novel features may not have arisen suddenly from scratch, but rather by tweaking and re-using a relatively small number of ancient developmental programmes,” said Gills.