Whiskers are touch antennas evolution bolted onto mammal faces
Vibrissae—whiskers—are specialized sensory hairs that let most mammals detect air currents and objects for navigation, hunting, and spatial sense. They cluster above eyes, on chins, forelegs, near ears, and above upper lips; monotremes lack them while non-human primates and nocturnal species rely heavily.
The name comes from the Latin for vibrate, after the constant quiver seen on an otherwise motionless small rodent; doctors also use it for the coarse hairs inside human nostrils. The trait is ancient. The last common ancestor of all living mammals had whiskers, and a canal beneath the eye socket in Triassic cynodonts of the group Prozostrodontia hints that it arose even earlier. Every surviving mammal except the great apes keeps the ancestral whisker layout along with the facial muscles that move it.
A whisker shaft is keratin with no nerves, like any hair, but it is stiffer, thicker and longer than the fur around it, and it grows from a follicle wrapped in a blood-filled sinus packed with sensory nerves that feed the trigeminal nerve. On the snout, the long whiskers stand in an ordered grid of rows and arcs, short at the front and long at the back. In mice, rats, hamsters, rabbits and cats each follicle is wired to 100 to 200 sensory neurons serving at least eight kinds of mechanoreceptor, and each whisker has its own patch in the brain's touch cortex.
Many animals sweep them actively. While hunting in dark, cluttered places, mice whisk at up to 25 times a second, one of the quickest movements any mammal makes. Social, tree-dwelling, nocturnal and small species tend to have the most and longest whiskers; a chinchilla's can exceed a third of its body length. Cats and other land mammals also carry a tuft just above the paw.
Water raises the stakes. Each seal whisker has about ten times the nerve supply of a rat's, over 300,000 nerve cells in total for the snout group, and manatees have roughly 600 around the lips; every body hair may be a whisker. Whales and dolphins lost their snout whiskers and grew some near the blowhole, and in dolphins the follicles now detect electric fields.
Source: Whiskers
