VACANT: one ecological niche. WANTED: an animal that can run like a horse, but can also nibble the most juicy leaves at the tops of trees. If you had to design such a beast from scratch, you would probably end up drawing a horse-like quadruped with a long neck. You would figure that the animal should be able to hear predators and alarm calls and you would equip it with well-hooded ears. Since it would receive alarm calls, it should also be able to send them. So you would equip it with a larynx. You would then pencil in a nerve running from the brain to the larynx, a distance of perhaps 20 cm. When checking your design against the real world, you would find a great similarity to the giraffe. However, the nerve to the larynx is actually several meters in length! From the brain, it runs down the neck to the chest where it loops round a major blood vessel and then returns up the neck to the larynx.
*First published as an article in the FASEB Journal (1993), volume 7, pages 619-621.