Scientists had assumed the pectoral fins in fish and the forelimbs (arms and hands) in humans are innervated -- or receive nerves -- from the exact same neurons. After all, the fins on fish and the arms on humans seem to be in the same place on the body. Not so.

During our early ancestors' transition from fish to land-dwellers that gave rise to upright mammals, the source for neurons that directly control the forelimbs moved from the brain into the spinal cord, as the torso moved away from the head and was given a neck. In other words human arms, like the wings of bats and birds, became separate from the head and placed on the torso below the neck.

"A neck allowed for improved movement and dexterity in terrestrial and aerial environments," says Andrew Bass, Cornell professor of neurobiology and behavior, and an author on the paper. "This innovation in biomechanics evolved hand-in-hand with changes in how the nervous system controls our limbs."

Bass explained that this unexpected level of evolutionary plasticity likely accounts for the incredible range of forelimb abilities -- from their use in flight by birds to swimming by whales and dolphins, and playing piano for humans.

The research was authored by Leung-Hang Ma (first author) and Robert Baker (corresponding author), both of Department of Physiology and Neuroscience, New York University Langone Medical Center; Edward Gilland, Department of Anatomy, Howard University; and Bass. All four researchers are affiliated with the Marine Biological Laboratory, Woods Hole, Mass.

The National Institutes of Health and the National Science Foundation funded the research.

Note: If no author is given, the source is cited instead.

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