Why do all felines have white whiskers? Some people claim that their domestic cats have black whiskers - I haven't seen any. Priya, Chennai, India
A black cat hunts on a warm summer day. Her long black tail lashes as she probes the bushes. A mouse darts into nearby leaf litter. The cat follows, momentarily loses the trail, and then pounces. Her mouth opens for the kill. Where, precisely, is the mouse? The cat's yellow eyes are too close to focus on the wildly squirming mouse. The cat's white whiskers stiffen to form a sensitive field around her mouth. Her whiskers feel exactly where the mouse is from vibrations and air currents, and she bites.
"Most, if not nearly all felines of all sizes, do appear to have white whiskers," says internationally renowned researcher Frank Rice of Albany Medical College, although, after a diligent search, Rice was able to find one black cat in his neighbourhood with black whiskers.
Why are most cats' whiskers white?
Normal cat hair comes in various colors - black, white, orange... But whisker hair differs from fur. It'sthicker, the roots delve deeper and a dense, tough bag filled with blood vessels and nerves surrounds the whisker. For some reason, though, the cat whisker usually does not access (or, possibly, retain) melanin (the dye that colors hair) and, therefore, cat whiskers are white.
But that begs the question. Why don't whiskers tap the nearby pigment supply?
Early on, when a cat is an embryo, the whiskers and pigment cells form in the same skin layer (which implies pigment access) says biologist Robert Dykes of McGill University. As the whisker follicle matures, it gets enfolded by the next deeper skin layer. But Dykes can see no reason why this denies pigment access.
In fact, whiskers probably do tap the pigment supply, e-mails Rice. A whisker may start pigmented, but lose its colour before the whisker emerges from the top skin layer.
A whisker starts as a single ring of skin cells at the root. Soon, though, a new ring of skin cells develops at the root, and this new ring pushes the older ring up, toward the skin surface. In this fashion, ring-by-ring, a whisker is born - formed of concentric rings of skin cells. The concentric rings that form the base of the whisker cone are colored, because the lowest rings pick up pigment from melanin cells at the whisker root. But, as new cells push the cone of skin cells upwards, surrounding tissue squeezes the cell cone inward and the skin cells die. Eventually the cone emerges from the skin as a whisker, composed of compressed dead skin cells.
In the compacting process, the skin cells not only die, but they lose pigment as they rise to the skin surface. So, it's "no surprise" that whiskers are often white, says Rice.
The mystery deepens. Remember the black cat Rice found with black whiskers? Why do the dead skin cells that form those black whiskers retain their melanin? Likewise, Rice asks, how do people with dark hair and animals with dark fur end up with dark hair, since the hair follicles lose melanin as they get pushed upwards by the new ring of skin cells below?
By the way, when the heart pumps blood into the tough bag surrounding the whisker, the pressure increases. This means individual whiskers are "held more rigidly" and are jammed closer to nerve receptors, which makes the whiskers extremely sensitive to "even slight mechanical stimuli," writes biologist Kevin Fox of Cardiff University, Wales in his book, Barrel Cortex. So, whiskers provide the cat with "essentially the same information that our hands provide to us concerning the texture, contour and other tactile properties of an object," e-mails Dykes.
Interestingly, the brain structure (barrel cortex) that receives whisker information is somewhat similar to the visual cortex.
But cats don't 'see' with their whiskers. Instead, Fox likens whiskers to hands feeling something in the dark. Hands move to feel the object, whereas eyes receive information in "one big picture."
Further Reading:
- Barrel Cortex Barrel Cortex by Kevin Fox, Cambridge University Press ƒo
- Somatotopic projections of mystacial vibrissae on cerebral cortex of cats, by R.W. Dykes et al, Journal of Neurophysiology, Vol 40, Issue 5 997-1014 ƒo
(Answered August 11, 2008)
April Holladay lives in Albuquerque, New Mexico. Her column, WonderQuest, appears every second Monday of the month on globetechnology.com. To read April's past columns, please visit her website . If you have a question for April, visit this information page .
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