Despite centuries of attempts to enable humans to fly without external assistance, we remain unable to propel our bodies into the air.

Turns out it’s not just because we don’t have wings. A recent study published in Science Advances explains that specific molecular characteristics distinguish birds from other creatures, and these differences allow birds to flap their wings and fly.

Previous studies proved that the ability of mammals and reptiles to walk is embedded within their spinal cords. This new study by Prof. Avihu Klar at the Hebrew University of Jerusalem and Prof. Claudio Mello from Oregon Health and Science University found that the ability to fly is embedded in birds’ spinal cords.

Hebrew University Prof. Avihu Klar. Photo courtesy of HUJ

Examining the neural networks of chicken and mice embryos revealed that the genetic coding of the ephrin-B3 molecule in birds is fundamentally different than in mammals and reptiles.

“The molecule ephrin-B3 is present in mammals but mutated or absent in birds. This simple but profound difference is what allows birds to flap their wings and take flight,” said Klar.

Rodents have this molecule in its fullest form and therefore step from left to right with their front and back limbs. However, mice with an ephrin-B3 mutation move with a synchronous jumping motion of both left and right sides at the same time, similar to birds.

The study, funded by the Israel-US Binational Foundation, “provides a clue to the evolutionary enigma: How did the nervous system evolve to support stepping, flying and swimming?” said Klar.

“It paves the way for future experiments to reveal the evolution of neuronal networks that enable the different modes of movement of legs and hands, a characteristic of bipedal animals such as birds and human.”