Analysis of neural networks explains why humans cannot fly

Analysis of neural networks explains why humans cannot fly

A study conducted by researchers from the Hebrew University of Jerusalem and the Oregon Health and Science University has identified the evolutionary reason

A study conducted by researchers from the Hebrew University of Jerusalem and the Oregon Health and Science University has identified the evolutionary reason why a human cannot achieve flight, with neural networks found to be crucial to our inability to fly, not just an inherent lack of wings. Their research is published in Science Advances.

Replicating a bird’s ability to fly has captivated humanity for centuries; however, without the aid of external mechanisms such as aeroplanes, helicopters, or hot air balloons, soaring through the skies of our own accord still evades us – with scientists and aeronautic designers long pondering what makes us mammals so dissimilar from birds.

For the longest time, research has been fixated on the structural factors that make birds so distinguishable, such as wings, although this still did not provide a definitive answer. Nevertheless, this novel study has indicated there are specific molecular characteristics that separate birds from other animals, which allows them to achieve flight.

Prior investigations had uncovered that mammals and reptiles are able to walk due to a genetic coding within their spinal cord, with this new research discovering that a bird’s ability to fly is likewise embedded in their spinal cords. To investigate this, the team analysed the neural networks of mice and chicken embryos, finding one distinct fundamental difference between birds, and mammals and reptiles – the genetic coding of the ephrin-B3 molecule.

Professor Avihu Klar, the leader of the study from Hebrew University of Jerusalem’s Faculty of Medicine, said: “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.”

Rodents express this molecule in its most complete form, meaning that they move in a stepping motion from left to right with their front and back limbs; however, mice with a mutation of ephrin-B3 demonstrate a simultaneous jumping motion of both sides, akin to that of a bird.

The results from the research solidify that genetic changes over time – evolution – supported birds in developing neural networks that stimulate an extremely coordinated movement pattern, allowing for the simultaneous flapping of wings.

Klar said: “Our study provides a clue to the evolutionary enigma: How did the nervous system evolve to support stepping, flying, and swimming. It paves the way for future experiments to reveal the evolution of the neural networks that enable the different modes of movement of legs and hands, a characteristic of bipedal animals, such as birds and humans.”


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