Humans are just modified fish

Monash University

A white variation of the Australian Lungfish, neoceratodus forsteri. Image: hidesy/iStockphoto Three Australian fish – including the iconic lungfish – have provided an insight into the evolution of human beings. A team of scientists led by Professor Peter Currie, Australian Regenerative Medicine Institute at Monash University and Dr Nicholas Cole, University of Sydney, have discovered how the muscles controlling the pelvic fins of some fish have cleared the way for the evolution of back legs in higher animals. This innovation gave rise to the tetrapods, or four-legged creatures, along with our distant ancestors who made the first steps onto land some 400 million years ago. Professor Currie said the genetics of a fish are not vastly different to our own. “We have shown that the mechanism of pelvic muscle formation in bony fish is transitional between that in sharks and in our tetrapod ancestors. “By examining the way the different fish species generated the muscles of their pelvic fins we were able to uncover the evolutionary forerunners of the hind limbs. Humans are just modified fish,” said Professor Currie. Scientists have long known that the ancient lungfish species are the ancestors of the tetrapods. These fish could survive on land, breathing air and using their pelvic fins to propel themselves. Australia is home to three species of the few remaining lungfish – two marine species and one inhabiting Queensland’s Mary River basin. There have been big gaps in the knowledge of these fish until now. Most of the conclusions have been drawn from fossil skeletons, but the muscles critical to locomotion cannot be preserved in the fossil record. The scientists used fish living today to trace the evolution of pelvic fin muscles to find out how the load bearing hind limbs of the tetrapods evolved. To find differences in pelvic fin muscle formation, the researchers compared embryos of the descendants of species representing key turning points in vertebrate evolution. They studied primitive cartilaginous fish: Australia’s bamboo shark and its cousin, the elephant shark; and three bony fish: the Australian lungfish, the zebrafish and the American paddlefish. The scientists genetically engineered fish to trace the migration of precursor muscle cells in early developmental stages as the animal’s body took shape. These cells in the engineered fish emitted red or green light. The team found that the bony fish had a different mechanism of pelvic fin muscle formation from that of the cartilaginous fish, a mechanism that was a stepping stone to the evolution of tetrapod physiology. The full research article, Development and Evolution of the Muscles of the Pelvic Fin can be viewed at PLoS Biology. Editor's Note: Original news release can be found here.