Again last weekend, I failed to cut my daughter's hair, even though I have repeatedly promised that I would. She is 18 months old, and has bouncy blonde curls that fall in front of her face, causing her to continually blow upwards to clear her knee-high view of the world. She definitely needs her curls cut, yet I cannot bring myself to take the scissors to them. Cutting her hair will be the first sign that she is not a totally natural human being, but being formed.
This cut will be a rite of passage; it is for most of us. My mother still has my first severed dark curl. I, too, will treasure my daughter's. It is the only piece of another human being's body that we can safely own. My boyfriend has a lock of his father's hair, cut as he lay slowly dying. From birth to death, our hair is crucial to life.
In other mammals, hair conserves body heat by insulating against the cold; human hair seems largely to have lost its purpose (still, the average number of hairs on a head is 150,000, growing at a rate of 1cm a month). Yet the arrival of hair, its changing thickness and colour, and eventual, almost inevitable greying and loss are huge landmarks for each of us.
In the womb, we are all covered with a layer of down called lanuga, which is usually shed on or shortly after birth. Over the next first few months, fine, short, unpigmented hairs, called vellus, appear. Vellus covers every part of our bodies except the palms of our hands and the soles of our feet. At puberty, this hair becomes longer, coarse and more heavily pigmented, and is called terminal hair. It appears in all the adult places - armpits, the pubic mound and, in men, on the face, chest and even back. It is at this hirsute stage that we begin to fight against the flow of our locks.
If we are female, we become obsessed with hair removal. Several years ago two American artists, Hannah Bonner and Mary-Charlotte Domandi, conducted a survey using two silhouettes of naked women. On one silhouette, women were asked to shade in the body hair they had naturally; on the other, where they had hair left after removal. The results revealed a secret world of womanly hairiness. Thirty-five per cent of the respondents had moustaches, 30% chin or neck hair. Half had hair on their chests. (The recent Channel 4 billboard advertising the Model Behaviour series - "I let my boyfriend pluck my nipples" - was meant to shock.) Yet on the after-removal silhouettes, all evidence of body hair vanished. As Germaine Greer wrote: "However much body hair a woman has, it is too much."
Men, conversely, become over-concerned about hair loss. Baldness has always implied low social status, an image that the crew cut consciously plays upon. Prisoners, army recruits, Nazi collaborators, and those believed to have lice have all traditionally had their heads forcibly shaved.
Bizarre cures for baldness have abounded. The biblical prophet Elisha resorted to rubbing bear grease on his scalp; Hippocrates applied sheep's urine; the early Romans used chicken dung. Some have resorted to disguise; Julius Caesar pioneered the forward-flowing combover. The only sure-fire way of preventing baldness is castration: eunuchs never go bald.
Every year, new potential cures are marketed. Most recently, Propecia arrived in the UK from America, where it is widely available on private health plans. The NHS, however, considers gradual baldness in men - alopecia androgenetica - a cosmetic, not a medical matter, and currently Propecia has to be bought privately over the internet. But sudden baldness - alopecia areata, which mostly affects women - is regarded as a disease, and long-term sufferers will be treated first with steroid creams; then minoxidil lotion (originally a treatment for high blood pressure until patients discovered their hair started regrowing, too); then, if all else fails, ultraviolet light therapy.
Hierarchies of sex, race and class have all been founded on hair. Examples of the display of power through topknots are numerous: 19th-century racial theories equated "woolly hair" with lower mental abilities; a fashionable style for a Victorian lady would take her maid several hours to execute, a clear display of her status and wealth; the longer a judge's wig, the higher position he may hold.
Next weekend - I promise - I will cut my daughter's hair for the first time. And a lifetime of being judged by her hair length will begin.