Human Hair : A Biological Necessity
Hair is a characteristic feature of mammals, which are commonly known as ‘Hairy quadrupeds’ — a group of animals that mark the climax of evolution. Also, mammals are the dominant animals in the world today, due partly to their ability to regulate body temperature in the face of variations in environmental temperature. This requires regulation of heat production and heat loss by the body. Hair plays an important role in regulating the latter. Impulses from the brain (hypothalamus) cause the hair to stand on ends, thereby enclosing an insulating layer of air just outside the skin. This layer reduces the loss of heat by radiation.
Even among mammals, man marks the climax of evolution and possesses the most complex and highly developed brain as well as the longest hair on head. This feature cannot be without significance. It cannot be a matter of mere chance or a mistake by Nature, because if the tail has been lost, the hair could have been lost too. Rather, there are numerous features in the human body that show retrogression. Some of the anatomical ones are :
– Loss of opposability of the great toe;
– Loss of hair from body;
– Teeth becoming smaller and fewer, and changing shape;
– Shortening of the muzzle and jaw symphysis;
– Loss of jaw power;
– Diminution in strength of zygomatic and temporal arch.
And, some of the ontogenetic features are :
– Gill-clefts, of which there are four in the embryo;
– Tail indicated by 4-5 bones at the lower terminus of the spine, coalesced in the adult into the coccygeal bone, which is concealed beneath the skin;
– The lanugo / foetal hair covering the entire body except palms and soles;
– Power of grip of newborn during the first few weeks of its life.
Some organs in the human body have become vestigeal, i.e., they are present, but functionless, such as :
– Vermiform appendix;
– Bands of muscles for moving ears;
– Hair-erecting muscles of the scalp;
– Dermal muscles for twitching retained in the face only;
– Third eyelid / nictitating membrane.
Even senses of smell and hearing are not so acute in man as in some other mammals. On the contrary, the hair on the head region in man has increased manifold as compared to other mammals. It thus follows clear that Nature is operating by an unknown mechanism, following a definite plan, and gets rid of certain features and improves upon others, as per requirement.
The dense and long growth of hair on the head region shows that the body is trying to increase the surface area for some particular function. Such a trend to increase the surface area is seen in every system of the body, e.g., highly coiled intestines with finger-like villi on their inner surfaces for absorption of digested food; alveoli in the lungs for exchange of O2 and CO2; glomerular capillaries in the form of a bunch, and coiled tubules in the kidneys where urine filtration takes place. The circulatory and nervous systems show extensive branching to reach every nook and corner of the body. The following fact shows the extent to which an increase in the surface area can be achieved by the body : If all the blood vessels in the body were straightened out and placed end to end, they would be 1,00,000 miles long, long enough to go round the equator four times. Even the surface of the human brain has maximum fissures (folds) corresponding to its increased mental abilities. The results that will be produced by decreasing the surface area at these points should be easy for all to imagine.
In plants also, the leaves are innumerable and flattened to increase the surface area for photosynthesis, and extensive branching of the root system provides increased surface area for absorption of water and minerals.
a) Functions of Hair
Hair perform a variety of functions. Some of these are listed below :
– Participate in the body’s sensory apparatus. The shaft transmits the sensation of pressure to nerves at the base of hair follicles;
– Trap an insulating layer of still air just outside the skin, and thereby reduce loss of heat by radiation;
– Provide protection from damaging effects of the ultraviolet (UV) radiation in sunlight;
– Act as storehouse of trace elements, such as, zinc, chromium, etc;
– Act as graveyard of harmful elements, such as, lead, arsenic, etc;
– Hair follicles can make androgenic hormones;
– The hair on scalp, apart from providing protection from midday sun, beautify the body (Bald men are desperate, and would pay any price to get hair back on their heads);
– Keep out coarse dust particles, e.g., eyelashes, hair in the nostrils and external auditory canals;
– Eyebrows prevent water or sweat from falling into eyes, due to their location and particular direction;
– Axillary and pubic hair lessen friction between limbs and body, and between limbs, respectively, during locomotion. As epigamic areas, they are concerned with social and sexual communication, either visibly or by scent from glands associated with hair follicles;
– Axillary hair provide larger surface area for evaporation of sweat;
– Beard and moustache are embellishments which establish maleness. Mostly males are decorated in Nature, e.g., lion, peacock and other birds, deer, etc.
b) Is Hair Lifeless ?
Hair is erroneously considered lifeless because of lack of any visible connection with the brain. But, the brain is not controlling /communicating with our body through nerves alone. Hormones, which are chemical mediators, also regulate various body functions. The immune system of the body fights infections with the help of co-ordinated action of cells, which have no visible connection with each other or with the brain. So, presence or absence of nerves alone cannot determine the connection of a particular part of the body with the brain. If hair was really dead to the brain, then how does the brain come to know that hair has been cut, and responds by growing it again to a specific length. Once the specific length has been attained, further growth ceases. Thus, undoubtedly, the brain is well aware of the condition of hair, cut or uncut, even upto its tip ! This is a sure sign of life. Thus, by cutting our hair, we are actually putting extra load on our body, as the energy and the raw materials (protein, pigment, etc.) required for growing hair time and again would be manifold as compared to the amount required for their maintenance only. And, hair, like any other living organ of the body, responds to ageing — in its variations in length, denseness of growth, and greying. The condition of health of a person is also reflected in hair — in its lustre, shine, growth patterns, etc.
Lack of sensation in hair along its shaft (visible part of hair) is no indication of it being dead, for, even the brain shows no such sensation. There is a group of animals (phylum Porifera), which do not possess a nervous system at all. A blow to any part of their body produces no response whatsoever. Do we call these animals lifeless ? Similarly, most plants do not show any sensation either.
Further, a part that we call ‘dead’ may be without sensation, but definitely not without function. Rather, its function is as important as any living part of a body, if not more. For example :
– What would be the fate of an egg without the shell ?
– What would be the condition of the body’s living cells without the covering of the dead cells, i.e., upper layers of skin ?
– How can teeth perform their function without enamel ?
– What life would a bird lead without feathers ?
– How would many freshwater animals overcome unfavourable conditions and not become extinct without cysts ?
– How would majority of plants survive and propagate as a species without formation of special devices meant for dispersal of seeds ?
Actually, different parts of a body or different cells cannot be categorised as useful / not useful. Each is only specially modified to perform different function(s) for the benefit of the same individual. What the cells of a kidney can do, the cells of pancreas cannot. That does not mean that the former are more important than the latter or vice versa.
Latest researches with newer techniques are adding more and more information to the existing knowledge. For example, although synthesis of protective keratin is clearly a major function of the epidermis, the discovery of an immunoregulatory role for the epidermis has revolutionized concepts of its importance in the immune defense systems of the host. In addition to melanocytes, human epidermis contains Langerhans cells. They are looked upon as ‘sentinel’ cells of the immune system, as their secretion enhances the immune reponse and is involved in the body’s systemic reaction to infections and injury. Also, the concept that the role of kerantinocytes themselves is confined to the synthesis of a horny protective outer covering for the skin has also become outmoded. Keratinocytes secrete a number of immuno-stimulatory highmolecular-weight peptides, collectively termed epidermal cytokines, which may have profound influence on the body’s capacity to mount immune responses to viral or bacterial infections or to cancerous growths.
c) Hair vs Nails
It is often commented / projected that hair and nails are similar. But even a superficial study of the two shows them to be different from each other. Whereas the hair grows from a tubular pit (hair follicle), formed by sinking in deep of the most actively dividing layer of the skin (stratum germinativum) into the lower dermis, the nails arise from an almost horizontal invagination of epidermis. Further, the base of every follicle bulges out forming an inverted cup, that fits over a small stud of dermis, the dermal papilla. It receives blood capillaries for nourishment and nerve fibres to make the hair sensitive. The wall of the hair follicle bulges out to form one or two oil glands, known as sebaceous glands, the secretion of which lubricates the hair. Rudiments of hair and mammary glands are similar in the first stages of their development. An involuntary muscle is also attached to the base of every hair for bringing about movement as a response to cold or fright. Pigment melanin, characteristic of skin and known for protecting from ultraviolet rays of sun, is added to the shaft of the hair as it grows.
A hair is a fine cylindrical filament. It shows three regions in cross-section : a central pith or medulla, a middle cortex, and an outer cuticle. The medulla frequently contains air spaces. The cortex has pigment granules in intercellular spaces. The cuticle is composed of a single layer of scaly denucleated cells. Within the follicle, the hair is surrounded by two additional layers of cells : inner Huxley’s layer and outer Henle’s layer.
Hair may be variously coloured. Colour of hair depends on : i) the colour and amount of pigment in the cortex, ii) the nature of hair surface, whether smooth or rough, and iii) the amount of air in the intercellular spaces of the medulla.
None of these features is associated with the nails, which consist of firmly cemented keratinised cells, flattened horizontally to the surface.
Structurally also, hair is extremely strong, and resists breaking due to its elasticity and flexibility. Strength of hair can be estimated from the following facts : a human hair laid on a bar of steel and then passed through a cold rolling mill would leave an imprint on the face of the steel; a hair of a man’s beard is about as strong as a copper wire of the same dimension; if a rope were made out of strands of long hair, it would be strong enough to lift an automobile. Nails, on the other hand, are very brittle and rigid, breaking off easily. Hair are countless (upto 1,25,000 on head region alone), thereby increasing the surface area, as if to meet a specific requirement. Nails number only twenty in an individual.
The differences between the two do not end with the structural features. Their growth patterns are also not identical. Hair follicles undergo cyclic activity, exhibiting three periods : active phase, anagen; transition phase, catagen; and resting phase, telogen. The nails, on the other hand, grow continuously with no periods of rest.
Even the body’s response towards the two is totally different. Our body, throughout life, tries to maintain a particular length of hair. And if hair is cut anywhere, the body responds by growing it again to the specific length. This clearly indicates a link of the brain with the hair all along its length. The body shows no such response to the nails, which grow from birth to death at the same rate, irrespective of whether cut or not. If their free edges were protected from wear, they would extend to prodigious lengths, growing in a twisted manner like a ram’s horn. Nails grow about 0.1 mm per day, or roughly one third as rapidly as hair.
Practically also, hair does not interfere in any daily activity, whereas it is impossible to work with long nails. And even if not cut, nails generally break off on their own; rather it takes great effort to maintain nails, even upto a short length. Whereas, the base of the hair becomes club-shaped and gets anchored to the surrounding follicular tissue by fibrous rootlets, prior to its shedding till a new shaft starts forming in its place.
Many systemic diseases alter the appearance and growth patterns of hair. A number of factors can also alter normal nail growth, thereby making them good indexes of health of individuals. But because of their ready response to so many internal and external factors, and because changes in them occur without a known reason, signs of abnormality can be misleading or difficult to interpret.
The development of nails into flattened plates reflects the discontinuation of their use for digging, or for defending and attacking. In contrast to the long list of functions of hair, only one function can be attributed to nails — protection of the tips of digits giving them firmness, and that too is limited to the part in contact with the skin. On the other hand, hair carries out the majority of its functions while its shaft has no contact with the skin.
To sum up, if there is anything on the head that can be compared with the nails, it is dandruff!
It is also argued that hair has been lost from the body in man, because the body is kept covered. If that be the case, then instead of being retained, the axillary hair because of its location and the pubic hair because it has been covered ab initio, should have been the first to go. Also, the hair on the face, neck and hands should have remained.
There are sound frequencies man does not hear; light waves, that make everything visible, man does not see; odours that man does not smell; there are animals that do not see as many colours as man does; some things man can neither see nor deny, such as emotions, bond between mother and child, force of gravity, etc. So, if there are things man does not see, hear, or smell, does it imply their absence ? Just as an ant cannot comprehend the size and shape of an elephant, life and its processes are beyond human comprehension in the present state of knowledge. The vast solar system, which is beyond reach even today, is just a speck in the universe ! Even man’s smallness is beyond our comprehension.
Nature knows best what to discard or retain. Whatever is retained is not without purpose. If we are unable to explain something, it does not mean that it has no significance. We must look for an explanation, rather than deny the role or existence of something we do not understand.
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