Recurrent Laryngeal Nerve
This animal nerve is interesting because of its circuitous route to its destination. It originates in the head, passes down into the chest and loops around the aorta before returning to the upper neck to serve the larynx. In humans, this adds a few superfluous inches, but in giraffes, the nerve must travel the entire length of the neck, before turning around and coming back to where it almost started!
It's often used as an example of biological evolution's lack of foresight: the nerve originally served the gills of our fish ancestors, but – over many years – as the aorta retracted into the thorax, the nerve was dragged along with it. Since evolution can only act upon its genetic starting materials, it is incapable of performing the type of complex, de novo rewire that would cut out the useless intervening nerve length.
http://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve
It's often used as an example of biological evolution's lack of foresight: the nerve originally served the gills of our fish ancestors, but – over many years – as the aorta retracted into the thorax, the nerve was dragged along with it. Since evolution can only act upon its genetic starting materials, it is incapable of performing the type of complex, de novo rewire that would cut out the useless intervening nerve length.
http://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve
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