Human Limbs Share A Gene From Cartilaginous Fish Gills, New Study Says

About a century ago, scientists discarded the findings of a study which showed that human limbs evolved from gills because it lacked fossil evidence. However, a new study revealed that human limbs actually share a gene with the gills of cartilaginous fish such as sharks, rays and skates. The study was printed in the journal Development.

Karl Gegenbaur, a German anatomist and a strong supporter of Darwin's theory of organic evolution, presented a theory that limbs evolved from the gill arch of cartilaginous fish in 1878. Unfortunately, there is nothing in the fossil record that can support his theory, according to  Daily Mail.

Today, the researchers from the University of Cambridge have reinvestigated Gegenbaur's theory utilizing the latest genetic techniques on embryos of the small skate. They discovered resemblances between the genetic mechanism that was used in the growth of its gill arches and the human limbs.

The scientists said that the gene, which is called "Sonic hedgehog", plays an important role in identifying the form and number of digits and ensuring that everything is in the exact place. It also maintains the growth of the limb skeleton. "In a hand, for instance, Sonic hedgehog tells the limb which side will be the thumb and which side will be the pinky finger," said Dr. Andrew Gillis, the lead author of the study from the University of Cambridge.

New York Post reports that the researchers discovered that the Sonic hedgehog gene determines the development of gill support structures, which is called branchial rays. Neil Shubin, an evolutionary biologist at the University of Chicago said that the rays are behaving like digits and what Gillis is seeing is that some of the genetic processes that shape and pattern gill rays are essential to the development of limbs with finger and toes. He further said that it is a very interesting insight.

Dr. Gillis said that the experiment could be interpreted as evidence that human limbs have a genetic program with gill arches because the fins and the limbs evolved by transformation of a gill arch in ancestral vertebrae, as suggested by Gegenbaur. On the other hand, he explained that these structures evolved distinctly, but re-used similar pre-existing genetic programme.

He further said that without fossil evidence, it remains a mystery. Hence, he stated that it is a fascinating discovery because it delivers evidence for an important evolutionary link between the branchial rays and the limbs.