Hair
The Mammalian Miracle Product
Very few animals subject their living cells to the direct insult of the environment. The role of skin (or integument) is largely to protect living cells from the environment. Many creatures fulfill this role by exposing dead cells or a coating of inert secretion to direct environmental contact--- the bark of trees, the cuticle of arthropods and the dead, keratinized cells of our own epidermis are examples. When live cells must be subjected, as in the digestive system, they are often protected by a layer of mucus that is constantly renewed. When you have a cold, your respiratory mucosa goes into overdrive.
Given the importance of the integument, it should not be surprising that it has evolved into a very complex, multifunctional organ, and being outward-facing, it should also not be surprising that many of its amazing capacities involve excretion, that is, the secretion of materials to the outside of the animal. In mammals, skin is a bewildering forest of tiny factories whose products depend on their location on the body as well as the function of the product--- sweat glands, various oil glands, odor glands, wax glands, and hair. Hair is one of the defining characters of mammals, just as feathers are of birds. The character of the hair varies enormously across mammalian species, and even varies greatly with location on the body, but all mammals have hair (although adult whales have lost most of it).
Hair is a secreted product of an epidermal follicle, a complex cluster of epidermal cells sunk below the skin surface and supplied with blood and nerves from the dermis. In the bottom of this follicle are stem cells whose rapid, unending division fill the follicular “vase” so full as to push these cells up the follicular tube and out above the skin surface, much like pushing toothpaste from a tube. The new cells soon die as they are filled with keratin--- hard keratin for the core (medulla) cells, softer for the intermediate cortex layer and hard for the outermost cuticle layer.
It isn’t hard to see how hair production is simply a highly modified and specialized version of the production of skin itself, that is, the continual production of cells whose function is to die, be filled with the keratin protein, and eventually be sloughed off as newer cell replace them from below. The same process that produces skin also produces hair, although the geometry of the latter process has changed enormously. Even so, the hair can be fine or coarse, dense or scarce, long or short, whiskers, eyebrows, or absent, and all can occur on a single animal.
Given this huge range of hair anatomy, some hair is worthy of collection as Found Objects. While backpacking in Alaska’s Brooks Range and North Arctic Plain, clumps of coarse, rather stiff hair caught my attention. This was caribou hair (or fur), but what made it collectible was not its mere presence (after all, 5,000 caribou had just ambled past), but a microscopic trait not visible to the naked eye. The hairs are hollow tubes, and the dead air space in the tubes makes caribou fur one of the most insulating furs. This, of course, is handy when the temperature sinks to minus 50o F, and accounts for the caribou’s success as an arctic grazing mammal. The evolutionary path to this hollow hair is probably that the follicle was modified not to produce the central hair medulla but continued making the outer two layers, resulting in a hollow hair. Such a small evolutionary twitch with such a large effect!
Musk ox also live in these same frigid zones as caribou but stay warm with a different modification of hair. Most mammal fur consists of two kinds of hair--- a relatively coarse hair and a fine hair often called the undercoat (vellus). As winter approaches, the fine, soft undercoat of the musk ox greatly proliferates to produce a thick insulating fur composed mostly of the soft undercoat. In spring, the musk ox shed this now unneeded undercoat by rubbing against bushes, leaving behind thick handfuls. I collected several large Ziploc bags full on my arctic hike, and found its spicy smell very pleasing. Weight for weight, this is the warmest wool known to man, the man being mostly native Inuits, who call it quiviut. The Inuits collect the quiviut from both wild and “domestic” musk ox, send it to a factory in Rhode Island to have it spun into wool skeins that are mailed back to Alaska to be knit into sweaters, hats, and so on by Inuit women. To pull a quiviut cap onto your head is truly to experience how much heat your head produces (and loses).
Many an unfortunate dog has learned a lesson about porcupines by way of a snootful of quills. Dogs may not know this, but porcupine quills are greatly enlarged and modified hairs, each provided with barbs at the outer end, and each capable of being detached from the porcupine by the nose of a dumb dog. It seems likely that the dogs are not aware that the quills stuck in their noses are homologous with the hair on their own bodies. Perhaps native Americans knew that as they collected and dyed quills to decorate several kinds of clothing, from moccasins to vests.
The extreme of porcupine quills occurs in the African porcupine. The tail and rear-facing quills of these animals are truly imposing, foam-cored and so large that the animal can rattle them as a warning signal. It is hard to resist collecting all that one finds littering the African habitat, and I never resisted. Indeed, there is a market for these beautiful, special hairs.
Is there other distinctive hair that would make an interesting found object? Well, surely other porcupine-like animals such as hedgehogs, American porcupines, and Madagascan tenrecs, but none of their quills have the size and caliber of the African porcupine. Mammalian hair is so variable in length, color and texture, but doesn’t cry out to be collected (except as fur, but we won’t go there). Still, if I had a chance to collect a fistful of wooly mammoth fur, I would probably hear the cry, “collect me.”