It is to me a puzzle of human evolution that people should have hair atop the head that grows and grows. The hair of our armpits, pubes, and elsewhere grows to a short and convenient length and then is replaced, while above our ears it does not stop. Until tools were made that might trim this growth, it was surely inconvenient for our remote ancestors to find their hair tangled in knots, infested with vermin, or flopping in front of the eyes. Yet has there been a single culture in which everyone shaves the head? Rather than following this sensible recourse, people have made the hair of their heads the focus of the elaborate practices, starting from the most basic males/short, females/long distinction and extending though the curling and scenting of antiquity to the salons and youth fashions of the present day.
The facial hair that appears on men at sexual maturity provides further opportunities for the semiotic signaling of style. Like the head-hair shared by men and women, it grows almost without limit,  far beyond the point where it would be an impediment, and thus it is that virtually every society trims the beard and some have shaved it off entirely.
We have reached a relaxation in this twenty-first century of America’s near prohibition on beards during my youth. During the time they were so very rare a beard was generally sorted among just a few possibilities according to specific characteristics. To see a beard would set off a chain of associations: of other eras or other lands, add a robe and you have Christ; a tousled appearance indicates a bum; a beret a bohemian; tweeds and glasses, a professor; a VanDyke means a psychiatrist; overalls a hillbilly; long hair above would indicate a nature boy.
Even the simple binary opposition beard/no beard has accumulated considerable signification through the centuries. In ancient Greece the beard was simply the sign of the adult man, distinguishing an individual from women and boys. In many cultures the beard was the badge of full civic membership and frequently people would or point to the beard as evidence of their responsibility. Plutarch tells of a Spartan who was asked why he wore a long beard, replied “So that I may see my grey hairs and do nothing unworthy of them.”  It seems also to have been customary to swear by the beard. In As You Like It  Touchstone says, “Stroke your chins, and swear by your beards that I am a knave” and in Troilus and Cressida, Nestor vows “By this white beard, I’ld fight with thee to-morrow.” 
Having naturally acquired associations with masculinity and thus strength, the beard was worn by soldiers until Alexander forbade them among his troops in 354 BCE, but, then, perhaps he just preferred a shorn look. The same military style was endorsed by Scipio Africanus among the Romans. After a time, many citizens, especially in cities, took to shaving and during the latter part of antiquity, beards then became associated with philosophers. Epictetus thought a beard “more beautiful than a cock’s comb” which should be preserved in part to clarify “the distinctions of the sexes.” “Adorn yourself then” he advises, “as man, not as woman. . . . Woman is naturally smooth and delicate; and if she has much hair (on her body), she is a monster and is exhibited at Rome among monsters. And in a man it is monstrous not to have hair; and if he has no hair, he is a monster; but if he cuts off his hairs and plucks them out, what shall we do with him? where shall we exhibit him? and under what name shall we show him? I will exhibit to you a man who chooses to be a woman rather than a man.” 
Instead of gender identity, the philosopher’s beard may signify, as it did for Diogenes, a disregard for social norms and in particular for artificial fussing over appearance. The association with philosophy was insufficient to protect the beard-wearer from satire. Poets made fun of beards not only with gibes about lice, goats, and dirt, but pretensions to wisdom as well in a way quite similar to Ernie Bushmiller’s Nancy cartoons featuring beatniks.  Even in societies where beard-wearing was the norm, such a secondary sexual characteristic may not necessarily be an erotic ornament. Many ancient gay Greek lyrics admonish the adolescent to make hay while the sun shines, warning that soon his beard will come and he will no longer be so attractive. 
From the philosopher to the man of religion may seem a small step, but the religious have struggled around the issue of beards for millennia. A beard may be a sign of asceticism or luxury, of unconcern for personal appearance or the excuse for elaborate trimming, scenting, and grooming. The somewhat obscure prohibition in Leviticus  against rounding “the corners of your heads,” and marring “the corners of thy beard” follows rules against divination and precedes an interdiction of cutting oneself “for the dead” and tattooing. (This has led some commentators to suggest it has more to do with avoiding pagan practices than with Jehovah’s preferences in hairstyle.) Every day on my bicycle route, I encounter Hasidic Jews whose beards provide visible signs of the strictness of their observance of those mysterious ancient lines.
Clement of Alexandria calls the beard “the mark of a man” and says “it is therefore unholy to desecrate the symbol of manhood.”  The beard was the mark of the Desert Fathers and other ascetics as it is today of the the Amish, Orthodox priests and monks, saddhus, and Sikhs. While the encouragement of Islam for facial hair is historically based in Mohammed’s beard,  the Christian Rascolniks in Russia so valued their own that they rebelled against Peter the Great’s condemnation of facial hair, saying they would rather lose their heads than their beards.
Though the Desert Fathers wore beards, many hermits and monks do not and indeed shave their pates as well as their chins. (In Thailand Buddhist monks go further yet, shaving even their eyebrows.) The Roman Emperor Julian grew a beard specifically to distinguish himself from the shaven Christian emperors before him, and to mark his connection to pagan Roman religion. The Western Church came to be very suspicious of beards, and they are forbidden for Roman Catholic clergy by a good many authorities, including the Canons of Edgar, the Council of Bourges, and an edict of Pope Alexander III. The disagreement was sufficiently strongly felt that it constituted part of the split between Eastern and Western churches in 1054.
My own beard feels a badge neither of religion nor irreligion. It is to some extent a fruit of laziness and the fact that my easily cut skin shrinks from the blade. It has the inconvenience of overdetermination in that it seems to some to tell more about me than it in fact does. Yet I would deceive myself if I did not acknowledge that the old connotations bore undeniable weight. Surely in the sixties beards were at once sensual and philosophical, artistic and counter-cultural, a sign both of hedonism and spiritual aspiration. It is a satisfyingly dense symbol, so comfortable that it is, I think, about fifteen years since I last shaved. Perhaps in another five I shall feel like having another unobstructed look at my own face.
Apologia for Shaving after Twenty Years
Because outward alteration can stimulate changes within,
and it is salutary now and then to seek to surprise
oneself and even the best of neighbors;
because too many people looking my way saw only the beard
and nothing else and we have regardless too many
barriers to the soul,
and bearded men, it is well known, are far too easy to draw;
for it was a sorry thing at best: worn, patchy, insecure, and
with little voice in the congresses of beards,
and thus even as it asserted my maturity, it conceded
that adolescence was still upon me;
because I suffer willy-nilly from excesses, and among those
excesses are pedantry and poetry, and I need no
signifiers to push the point;
for a smooth chin is a feminine thing, and the world would
still do well to be a bit more womanly;
for my masculinity is adequately evinced by impatience in
stores and traffic jams, and by my iron resolution
that no one should pass me on the bicycle path,
and thus the beard was superfluous;
for mine was a beard that meant youth and not age, and now
I am no longer young;
because after even more than twenty years the shock of seeing
my own face may have been -- oh! -- too great to bear;
for already the beard had grown white enough to show
the shadows of my own ghost too clear, and I fled,
I fled at last.
1. The longest recorded beard is generally conceded to be that of Hans Langseth which reached 17’ 6” (18’ 6” in some accounts). Contemporary contenders reach barely half that heroic length.
2. Plutarch, Apophthegmata Spartika 4.
3. 2. I, ii.
4. IV, v.
5. Arrian, Discourses of Epictetus, Book I.16 Book III.1.
6. A number of such mocking poems have been gathered at http://laudatortemporisacti.blogspot.com/2006/04/beards-and-philosophers.html.
For Bushmiller’s work see his Bums, Beatniks and Hippies/Artists & Con Artists.
7. V 277 “I hate the unkind hair that begins to grow too soon.” (Eratosthenes Scholasticus.
8. Lev. 19:27.
9. The Instructor, Bk III, Ch 3, 2.276 and 2.277.
10. Oddly, Muslims must not shave their beards (moustaches can go) yet they do shave public hair