When I went to school, all children wore school uniforms that included a sweater. It was navy blue with two narrow stripes -- one red, the other gold -- in a band that encircled the V-shaped neckline. Most of us had working-class parents and most wore sweaters hand-knitted by their mothers. Mine had been made by my aunt.

Then machine-knitted sweaters became available. They were more closely woven, smoother, immensely more fashionable and much more expensive than the old hand-knitted ones. They were perfect. I wanted one, but my mother refused. I envied my sweater-privileged friends and felt humiliated to be so ill-attired.

Today mass produced sweaters are relatively inexpensive, whereas anything hand-knitted costs hundreds of dollars. The latter often carry a small ticket saying that imperfections are part of the art and character of the sweater; that is, these imperfections are desirable and valued because they make it unique. They are evidence that the sweater is the time-consuming, painstaking, often loving, authentic work of human hands. They give it its "soul."

My musings about sweaters were prompted by thinking about the use of science in the search for human perfection. It is often said that nowhere are we at more ethical peril than when we undertake such quests. The Nazi horrors showed us the dangers of a political platform or public policy approach that uses science and technology to search for perceived biological "perfection" in ourselves, individually, and society as a whole.

Today, we can seek the perfect baby through designing it using genetic and reproductive technologies -- positive eugenics. The perfect copy of our self with cloning. The perfect war (risk free to us) with virtually controlled (disembodied) combat technologies. The perfect athlete with drug use or gene doping. The perfect body with cosmetic surgery.

Likewise, we can seek to eliminate those we see as imperfect -- negative eugenics. We use new technology to carry out "embryo biopsies" (preimplantation genetic diagnosis) on in vitro fertilized embryos to identify and discard those who are "defective." We use prenatal screening to identify fetuses with genetic or other disabilities, such as Down's syndrome, and abort them. And, most recently, we have a do-it-yourself test that can be used at 10 weeks of gestation to see if the baby is male or female. If we are having a baby of the "wrong" sex, we can abort it and "try again."

And, in a context that is relevant to all of us because we will all face death, we can seek both to achieve the perfect death and to eliminate imperfect people through euthanasia and assisted-suicide.

I want to propose that these interventions in search of the perfect and to eliminate the imperfect threaten the essence of our humanness -- our human spirit, that which makes us human and enables us to experience awe, wonder and the mystery of life, and through which we search for meaning. This latter search is of the essence of being human; we are meaning-seeking beings and, as far as we know, uniquely so.

Those who are religious define what constitutes the essence of our humanness as the soul -- the sharing in a Divine spark. It is extremely difficult to define what constitutes that essence for those who reject religion, but many such people believe -- or at least act as though -- such an essence exists. For instance, anybody who agrees that humans are "special" as compared with other living beings and, therefore, deserve "special respect," is manifesting such a belief.

However, some secular humanists expressly reject such a belief. They regard "preferencing humans" (seeing humans as special as compared with other animals or even robots) as wrongful discrimination in the form of what they call speciesism.

I propose a very important question we need to ask in deciding what we may and should not do with our new technoscience, that is, what is ethical or unethical: Does any given use of this science, in the search for human perfection, damage or destroy the essence of our humanness? That leads to the question of whether at least some imperfections are elements of that essence and of immense value as such. Just like the hand-knitted sweater, are they part of what makes each of us unique originals?

I once wrote elsewhere that I wondered why seeing the original of a famous painting is not only different from, but much more exciting than, seeing an exact copy -- at least, to me it is. (It turns out that some people prefer the copy. For instance, the Australian government built a replica of part of the Great Barrier Reef to reduce the number of tourists to the real reef in order to better protect it. Tourists from Japan preferred the replica to the real thing.)

Or we can think about how antiques lose their value if they are refinished -- when the many human hands that have touched the antique and the marks they have left have been erased, we consider that the antique is no longer authentic, that its priceless intangible essence is gone. In fact, we value such antiques less because in our later touching of them to alter them, they can no longer touch our imagination with the same profundity.

I believe that if we succeed in our search for human perfection -- or, perhaps, even if we just engage in it -- we will lose our authenticity, our human essence, our messy, old, much-touched soul. We will be like copies of masterpieces or like restored antiques: not originals, no longer unique, no longer the "real thing."

Just as we changed our minds about which was the most valuable sweater, the perfect machine-made or the "imperfect" hand-knitted one, perhaps the same will happen with respect to our natural, untampered-with, imperfect human selves.

Margaret Somerville is director of the Centre for Medicine, Ethics and Law at McGill University, and author of The Ethical Imagination: Journeys of the Human Spirit.