CAMBRIDGE, UK — A new study is shedding new light on a widely refuted century-old theory that proposed a link between human limbs and fish gills.

Science Daily reports that a research team from the University of Cambridge has found a possible evolutionary connection between our limbs and the gills of fish like sharks, rays and skate. The theory was first put forward in 1878 by German anatomist Karl Gegenbaur, but was dismissed due to a lack of fossil evidence.

According to the study, which was published in the journal Development, cartilaginous fish have gill support structures called branchial rays, which fan out in the same way fingers do.

The key is a gene dubbed 'Sonic hedgehog.' In humans, this gene determines where appendages like fingers will grow. It also keeps them growing to full size. The gene was named after the video game character by a researcher whose daughter was a fan of Sonic the blue hedgehog.

When the scientists studied skate embryos, they found the same gene was responsible for the formation of branchial rays. When inhibited early in development, the gene causes the branchial rays to grow on the wrong side. When inhibited later on, branchial rays grow on the correct side, but are fewer in number, suggesting that the underlying mechanism for growth is the same as in humans.

Despite the similarities, it's possible gills and limbs evolved separately and simply used the same growth mechanism. They could also be completely unrelated, just happening to use the same gene. Further research is needed to find out for sure and prove the theory true.

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