he first time I opened Peter Singer's ''Animal Liberation,'' I was dining alone at the Palm, trying to enjoy a rib-eye steak cooked medium-rare. If this sounds like a good recipe for cognitive dissonance (if not indigestion), that was sort of the idea. Preposterous as it might seem, to supporters of animal rights, what I was doing was tantamount to reading ''Uncle Tom's Cabin'' on a plantation in the Deep South in 1852.

Singer and the swelling ranks of his followers ask us to imagine a future in which people will look back on my meal, and this steakhouse, as relics of an equally backward age. Eating animals, wearing animals, experimenting on animals, killing animals for sport: all these practices, so resolutely normal to us, will be seen as the barbarities they are, and we will come to view ''speciesism'' -- a neologism I had encountered before only in jokes -- as a form of discrimination as indefensible as racism or anti-Semitism.

Even in 1975, when ''Animal Liberation'' was first published, Singer, an Australian philosopher now teaching at Princeton, was confident that he had the wind of history at his back. The recent civil rights past was prologue, as one liberation movement followed on the heels of another. Slowly but surely, the white man's circle of moral consideration was expanded to admit first blacks, then women, then homosexuals. In each case, a group once thought to be so different from the prevailing ''we'' as to be undeserving of civil rights was, after a struggle, admitted to the club. Now it was animals' turn.

That animal liberation is the logical next step in the forward march of moral progress is no longer the fringe idea it was back in 1975. A growing and increasingly influential movement of philosophers, ethicists, law professors and activists are convinced that the great moral struggle of our time will be for the rights of animals.

So far the movement has scored some of its biggest victories in Europe. Earlier this year, Germany became the first nation to grant animals a constitutional right: the words ''and animals'' were added to a provision obliging the state to respect and protect the dignity of human beings. The farming of animals for fur was recently banned in England. In several European nations, sows may no longer be confined to crates nor laying hens to ''battery cages'' -- stacked wired cages so small the birds cannot stretch their wings. The Swiss are amending their laws to change the status of animals from ''things'' to ''beings.''

Though animals are still very much ''things'' in the eyes of American law, change is in the air. Thirty-seven states have recently passed laws making some forms of animal cruelty a crime, 21 of them by ballot initiative. Following protests by activists, McDonald's and Burger King forced significant improvements in the way the U.S. meat industry slaughters animals. Agribusiness and the cosmetics and apparel industries are all struggling to defuse mounting public concerns over animal welfare.

Once thought of as a left-wing concern, the movement now cuts across ideological lines. Perhaps the most eloquent recent plea on behalf of animals, a new book called ''Dominion,'' was written by a former speechwriter for President Bush. And once outlandish ideas are finding their way into mainstream opinion. A recent Zogby poll found that 51 percent of Americans believe that primates are entitled to the same rights as human children.

What is going on here? A certain amount of cultural confusion, for one thing. For at the same time many people seem eager to extend the circle of our moral consideration to animals, in our factory farms and laboratories we are inflicting more suffering on more animals than at any time in history. One by one, science is dismantling our claims to uniqueness as a species, discovering that such things as culture, tool making, language and even possibly self-consciousness are not the exclusive domain of Homo sapiens. Yet most of the animals we kill lead lives organized very much in the spirit of Descartes, who famously claimed that animals were mere machines, incapable of thought or feeling. There's a schizoid quality to our relationship with animals, in which sentiment and brutality exist side by side. Half the dogs in America will receive Christmas presents this year, yet few of us pause to consider the miserable life of the pig -- an animal easily as intelligent as a dog -- that becomes the Christmas ham.

We tolerate this disconnect because the life of the pig has moved out of view. When's the last time you saw a pig? (Babe doesn't count.) Except for our pets, real animals -- animals living and dying -- no longer figure in our everyday lives. Meat comes from the grocery store, where it is cut and packaged to look as little like parts of animals as possible. The disappearance of animals from our lives has opened a space in which there's no reality check, either on the sentiment or the brutality. This is pretty much where we live now, with respect to animals, and it is a space in which the Peter Singers and Frank Perdues of the world can evidently thrive equally well.

Several years ago, the English critic John Berger wrote an essay, ''Why Look at Animals?'' in which he suggested that the loss of everyday contact between ourselves and animals -- and specifically the loss of eye contact -- has left us deeply confused about the terms of our relationship to other species. That eye contact, always slightly uncanny, had provided a vivid daily reminder that animals were at once crucially like and unlike us; in their eyes we glimpsed something unmistakably familiar (pain, fear, tenderness) and something irretrievably alien. Upon this paradox people built a relationship in which they felt they could both honor and eat animals without looking away. But that accommodation has pretty much broken down; nowadays, it seems, we either look away or become vegetarians. For my own part, neither option seemed especially appetizing. Which might explain how I found myself reading ''Animal Liberation'' in a steakhouse.

This is not something I'd recommend if you're determined to continue eating meat. Combining rigorous philosophical argument with journalistic description, ''Animal Liberation'' is one of those rare books that demand that you either defend the way you live or change it. Because Singer is so skilled in argument, for many readers it is easier to change. His book has converted countless thousands to vegetarianism, and it didn't take long for me to see why: within a few pages, he had succeeded in throwing me on the defensive.

Singer's argument is disarmingly simple and, if you accept its premises, difficult to refute. Take the premise of equality, which most people readily accept. Yet what do we really mean by it? People are not, as a matter of fact, equal at all -- some are smarter than others, better looking, more gifted. ''Equality is a moral idea,'' Singer points out, ''not an assertion of fact.'' The moral idea is that everyone's interests ought to receive equal consideration, regardless of ''what abilities they may possess.'' Fair enough; many philosophers have gone this far. But fewer have taken the next logical step. ''If possessing a higher degree of intelligence does not entitle one human to use another for his or her own ends, how can it entitle humans to exploit nonhumans for the same purpose?''

This is the nub of Singer's argument, and right around here I began scribbling objections in the margin. But humans differ from animals in morally significant ways. Yes they do, Singer acknowledges, which is why we shouldn't treat pigs and children alike. Equal consideration of interests is not the same as equal treatment, he points out: children have an interest in being educated; pigs, in rooting around in the dirt. But where their interests are the same, the principle of equality demands they receive the same consideration. And the one all-important interest that we share with pigs, as with all sentient creatures, is an interest in avoiding pain.

Here Singer quotes a famous passage from Jeremy Bentham, the 18th-century utilitarian philosopher, that is the wellspring of the animal rights movement. Bentham was writing in 1789, soon after the French colonies freed black slaves, granting them fundamental rights. ''The day may come,'' he speculates, ''when the rest of the animal creation may acquire those rights.'' Bentham then asks what characteristic entitles any being to moral consideration. ''Is it the faculty of reason or perhaps the faculty of discourse?'' Obviously not, since ''a full-grown horse or dog is beyond comparison a more rational, as well as a more conversable animal, than an infant.'' He concludes: ''The question is not, Can they reason? nor, Can they talk? but, Can they suffer?''

Bentham here is playing a powerful card philosophers call the ''argument from marginal cases,'' or A.M.C. for short. It goes like this: there are humans -- infants, the severely retarded, the demented -- whose mental function cannot match that of a chimpanzee. Even though these people cannot reciprocate our moral attentions, we nevertheless include them in the circle of our moral consideration. So on what basis do we exclude the chimpanzee?

Because he's a chimp, I furiously scribbled in the margin, and they're human! For Singer that's not good enough. To exclude the chimp from moral consideration simply because he's not human is no different from excluding the slave simply because he's not white. In the same way we'd call that exclusion racist, the animal rightist contends that it is speciesist to discriminate against the chimpanzee solely because he's not human.

But the differences between blacks and whites are trivial compared with the differences between my son and a chimp. Singer counters by asking us to imagine a hypothetical society that discriminates against people on the basis of something nontrivial -- say, intelligence. If that scheme offends our sense of equality, then why is the fact that animals lack certain human characteristics any more just as a basis for discrimination? Either we do not owe any justice to the severely retarded, he concludes, or we do owe it to animals with higher capabilities.

This is where I put down my fork. If I believe in equality, and equality is based on interests rather than characteristics, then either I have to take the interests of the steer I'm eating into account or concede that I am a speciesist. For the time being, I decided to plead guilty as charged. I finished my steak.

But Singer had planted a troubling notion, and in the days afterward, it grew and grew, watered by the other animal rights thinkers I began reading: the philosophers Tom Regan and James Rachels; the legal theorist Steven M. Wise; the writers Joy Williams and Matthew Scully. I didn't think I minded being a speciesist, but could it be, as several of these writers suggest, that we will someday come to regard speciesism as an evil comparable to racism? Will history someday judge us as harshly as it judges the Germans who went about their ordinary lives in the shadow of Treblinka? Precisely that question was recently posed by J.M. Coetzee, the South African novelist, in a lecture delivered at Princeton; he answered it in the affirmative. If animal rightists are right, ''a crime of stupefying proportions'' (in Coetzee's words) is going on all around us every day, just beneath our notice.

It's an idea almost impossible to entertain seriously, much less to accept, and in the weeks following my restaurant face-off between Singer and the steak, I found myself marshaling whatever mental power I could muster to try to refute it. Yet Singer and his allies managed to trump almost all my objections.

My first line of defense was obvious. Animals kill one another all the time. Why treat animals more ethically than they treat one another? (Ben Franklin tried this one long before me: during a fishing trip, he wondered, ''If you eat one another, I don't see why we may not eat you.'' He admits, however, that the rationale didn't occur to him until the fish were in the frying pan, smelling ''admirably well.'' The advantage of being a ''reasonable creature,'' Franklin remarks, is that you can find a reason for whatever you want to do.) To the ''they do it, too'' defense, the animal rightist has a devastating reply: do you really want to base your morality on the natural order? Murder and rape are natural, too. Besides, humans don't need to kill other creatures in order to survive; animals do. (Though if my cat, Otis, is any guide, animals sometimes kill for sheer pleasure.)

This suggests another defense. Wouldn't life in the wild be worse for these farm animals? ''Defenders of slavery imposed on black Africans often made a similar point,'' Singer retorts. ''The life of freedom is to be preferred.''

But domesticated animals can't survive in the wild; in fact, without us they wouldn't exist at all. Or as one 19th-century political philosopher put it, ''The pig has a stronger interest than anyone in the demand for bacon. If all the world were Jewish, there would be no pigs at all.'' But it turns out that this would be fine by the animal rightists: for if pigs don't exist, they can't be wronged.

Animals on factory farms have never known any other life. Singer replies that ''animals feel a need to exercise, stretch their limbs or wings, groom themselves and turn around, whether or not they have ever lived in conditions that permit this.'' The measure of their suffering is not their prior experiences but the unremitting daily frustration of their instincts.

O.K., the suffering of animals is a legitimate problem, but the world is full of problems, and surely human problems must come first! Sounds good, and yet all the animal people are asking me to do is to stop eating meat and wearing animal furs and hides. There's no reason I can't devote myself to solving humankind's problems while being a vegetarian who wears synthetics.

But doesn't the fact that we could choose to forgo meat for moral reasons point to a crucial moral difference between animals and humans? As Kant pointed out, the human being is the only moral animal, the only one even capable of entertaining a concept of ''rights.'' What's wrong with reserving moral consideration for those able to reciprocate it? Right here is where you run smack into the A.M.C.: the moral status of the retarded, the insane, the infant and the Alzheimer's patient. Such ''marginal cases,'' in the detestable argot of modern moral philosophy, cannot participate in moral decision making any more than a monkey can, yet we nevertheless grant them rights.

That's right, I respond, for the simple reason that they're one of us. And all of us have been, and will probably once again be, marginal cases ourselves. What's more, these people have fathers and mothers, daughters and sons, which makes our interest in their welfare deeper than our interest in the welfare of even the most brilliant ape.

Alas, none of these arguments evade the charge of speciesism; the racist, too, claims that it's natural to give special consideration to one's own kind. A utilitarian like Singer would agree, however, that the feelings of relatives do count for something. Yet the principle of equal consideration of interests demands that, given the choice between performing a painful medical experiment on a severely retarded orphan and on a normal ape, we must sacrifice the child. Why? Because the ape has a greater capacity for pain.

Here in a nutshell is the problem with the A.M.C.: it can be used to help the animals, but just as often it winds up hurting the marginal cases. Giving up our speciesism will bring us to a moral cliff from which we may not be prepared to jump, even when logic is pushing us.

And yet this isn't the moral choice I am being asked to make. (Too bad; it would be so much easier!) In everyday life, the choice is not between babies and chimps but between the pork and the tofu. Even if we reject the ''hard utilitarianism'' of a Peter Singer, there remains the question of whether we owe animals that can feel pain any moral consideration, and this seems impossible to deny. And if we do owe them moral consideration, how can we justify eating them?

This is why killing animals for meat (and clothing) poses the most difficult animal rights challenge. In the case of animal testing, all but the most radical animal rightists are willing to balance the human benefit against the cost to the animals. That's because the unique qualities of human consciousness carry weight in the utilitarian calculus: human pain counts for more than that of a mouse, since our pain is amplified by emotions like dread; similarly, our deaths are worse than an animal's because we understand what death is in a way they don't. So the argument over animal testing is really in the details: is this particular procedure or test really necessary to save human lives? (Very often it's not, in which case we probably shouldn't do it.) But if humans no longer need to eat meat or wear skins, then what exactly are we putting on the human side of the scale to outweigh the interests of the animal?

I suspect that this is finally why the animal people managed to throw me on the defensive. It's one thing to choose between the chimp and the retarded child or to accept the sacrifice of all those pigs surgeons practiced on to develop heart-bypass surgery. But what happens when the choice is between ''a lifetime of suffering for a nonhuman animal and the gastronomic preference of a human being?'' You look away -- or you stop eating animals. And if you don't want to do either? Then you have to try to determine if the animals you're eating have really endured ''a lifetime of suffering.''

Whether our interest in eating animals outweighs their interest in not being eaten (assuming for the moment that is their interest) turns on the vexed question of animal suffering. Vexed, because it is impossible to know what really goes on in the mind of a cow or a pig or even an ape. Strictly speaking, this is true of other humans, too, but since humans are all basically wired the same way, we have excellent reason to assume that other people's experience of pain feels much like our own. Can we say that about animals? Yes and no.

I have yet to find anyone who still subscribes to Descartes's belief that animals cannot feel pain because they lack a soul. The general consensus among scientists and philosophers is that when it comes to pain, the higher animals are wired much like we are for the same evolutionary reasons, so we should take the writhings of the kicked dog at face value. Indeed, the very premise of a great deal of animal testing -- the reason it has value -- is that animals' experience of physical and even some psychological pain closely resembles our own. Otherwise, why would cosmetics testers drip chemicals into the eyes of rabbits to see if they sting? Why would researchers study head trauma by traumatizing chimpanzee heads? Why would psychologists attempt to induce depression and ''learned helplessness'' in dogs by exposing them to ceaseless random patterns of electrical shock?

That said, it can be argued that human pain differs from animal pain by an order of magnitude. This qualitative difference is largely the result of our possession of language and, by virtue of language, an ability to have thoughts about thoughts and to imagine alternatives to our current reality. The philosopher Daniel C. Dennett suggests that we would do well to draw a distinction between pain, which a great many animals experience, and suffering, which depends on a degree of self-consciousness only a few animals appear to command. Suffering in this view is not just lots of pain but pain intensified by human emotions like loss, sadness, worry, regret, self-pity, shame, humiliation and dread.

Consider castration. No one would deny the procedure is painful to animals, yet animals appear to get over it in a way humans do not. (Some rhesus monkeys competing for mates will bite off a rival's testicle; the very next day the victim may be observed mating, seemingly little the worse for wear.) Surely the suffering of a man able to comprehend the full implications of castration, to anticipate the event and contemplate its aftermath, represents an agony of another order.

By the same token, however, language and all that comes with it can also make certain kinds of pain more bearable. A trip to the dentist would be a torment for an ape that couldn't be made to understand the purpose and duration of the procedure.

As humans contemplating the pain and suffering of animals, we do need to guard against projecting on to them what the same experience would feel like to us. Watching a steer force-marched up the ramp to the kill-floor door, as I have done, I need to remind myself that this is not Sean Penn in ''Dead Man Walking,'' that in a bovine brain the concept of nonexistence is blissfully absent. ''If we fail to find suffering in the [animal] lives we can see,'' Dennett writes in ''Kinds of Minds,'' ''we can rest assured there is no invisible suffering somewhere in their brains. If we find suffering, we will recognize it without difficulty.''

Which brings us -- reluctantly, necessarily -- to the American factory farm, the place where all such distinctions turn to dust. It's not easy to draw lines between pain and suffering in a modern egg or confinement hog operation. These are places where the subtleties of moral philosophy and animal cognition mean less than nothing, where everything we've learned about animals at least since Darwin has been simply . . . set aside. To visit a modern CAFO (Confined Animal Feeding Operation) is to enter a world that, for all its technological sophistication, is still designed according to Cartesian principles: animals are machines incapable of feeling pain. Since no thinking person can possibly believe this any more, industrial animal agriculture depends on a suspension of disbelief on the part of the people who operate it and a willingness to avert your eyes on the part of everyone else.

From everything I've read, egg and hog operations are the worst. Beef cattle in America at least still live outdoors, albeit standing ankle deep in their own waste eating a diet that makes them sick. And broiler chickens, although they do get their beaks snipped off with a hot knife to keep them from cannibalizing one another under the stress of their confinement, at least don't spend their eight-week lives in cages too small to ever stretch a wing. That fate is reserved for the American laying hen, who passes her brief span piled together with a half-dozen other hens in a wire cage whose floor a single page of this magazine could carpet. Every natural instinct of this animal is thwarted, leading to a range of behavioral ''vices'' that can include cannibalizing her cagemates and rubbing her body against the wire mesh until it is featherless and bleeding. Pain? Suffering? Madness? The operative suspension of disbelief depends on more neutral descriptors, like ''vices'' and ''stress.'' Whatever you want to call what's going on in those cages, the 10 percent or so of hens that can't bear it and simply die is built into the cost of production. And when the output of the others begins to ebb, the hens will be ''force-molted'' -- starved of food and water and light for several days in order to stimulate a final bout of egg laying before their life's work is done.

Simply reciting these facts, most of which are drawn from poultry-trade magazines, makes me sound like one of those animal people, doesn't it? I don't mean to, but this is what can happen when . . . you look. It certainly wasn't my intention to ruin anyone's breakfast. But now that I probably have spoiled the eggs, I do want to say one thing about the bacon, mention a single practice (by no means the worst) in modern hog production that points to the compound madness of an impeccable industrial logic.

Piglets in confinement operations are weaned from their mothers 10 days after birth (compared with 13 weeks in nature) because they gain weight faster on their hormone- and antibiotic-fortified feed. This premature weaning leaves the pigs with a lifelong craving to suck and chew, a desire they gratify in confinement by biting the tail of the animal in front of them. A normal pig would fight off his molester, but a demoralized pig has stopped caring. ''Learned helplessness'' is the psychological term, and it's not uncommon in confinement operations, where tens of thousands of hogs spend their entire lives ignorant of sunshine or earth or straw, crowded together beneath a metal roof upon metal slats suspended over a manure pit. So it's not surprising that an animal as sensitive and intelligent as a pig would get depressed, and a depressed pig will allow his tail to be chewed on to the point of infection. Sick pigs, being underperforming ''production units,'' are clubbed to death on the spot. The U.S.D.A.'s recommended solution to the problem is called ''tail docking.'' Using a pair of pliers (and no anesthetic), most but not all of the tail is snipped off. Why the little stump? Because the whole point of the exercise is not to remove the object of tail-biting so much as to render it more sensitive. Now, a bite on the tail is so painful that even the most demoralized pig will mount a struggle to avoid it.

Much of this description is drawn from ''Dominion,'' Matthew Scully's recent book in which he offers a harrowing description of a North Carolina hog operation. Scully, a Christian conservative, has no patience for lefty rights talk, arguing instead that while God did give man ''dominion'' over animals (''Every moving thing that liveth shall be meat for you''), he also admonished us to show them mercy. ''We are called to treat them with kindness, not because they have rights or power or some claim to equality but . . . because they stand unequal and powerless before us.''

Scully calls the contemporary factory farm ''our own worst nightmare'' and, to his credit, doesn't shrink from naming the root cause of this evil: unfettered capitalism. (Perhaps this explains why he resigned from the Bush administration just before his book's publication.) A tension has always existed between the capitalist imperative to maximize efficiency and the moral imperatives of religion or community, which have historically served as a counterweight to the moral blindness of the market. This is one of ''the cultural contradictions of capitalism'' -- the tendency of the economic impulse to erode the moral underpinnings of society. Mercy toward animals is one such casualty.

More than any other institution, the American industrial animal farm offers a nightmarish glimpse of what capitalism can look like in the absence of moral or regulatory constraint. Here in these places life itself is redefined -- as protein production -- and with it suffering. That venerable word becomes ''stress,'' an economic problem in search of a cost-effective solution, like tail-docking or beak-clipping or, in the industry's latest plan, by simply engineering the ''stress gene'' out of pigs and chickens. ''Our own worst nightmare'' such a place may well be; it is also real life for the billions of animals unlucky enough to have been born beneath these grim steel roofs, into the brief, pitiless life of a ''production unit'' in the days before the suffering gene was found.

Vegetarianism doesn't seem an unreasonable response to such an evil. Who would want to be made complicit in the agony of these animals by eating them? You want to throw something against the walls of those infernal sheds, whether it's the Bible, a new constitutional right or a whole platoon of animal rightists bent on breaking in and liberating the inmates. In the shadow of these factory farms, Coetzee's notion of a ''stupefying crime'' doesn't seem far-fetched at all.

But before you swear off meat entirely, let me describe a very different sort of animal farm. It is typical of nothing, and yet its very existence puts the whole moral question of animal agriculture in a different light. Polyface Farm occupies 550 acres of rolling grassland and forest in the Shenandoah Valley of Virginia. Here, Joel Salatin and his family raise six different food animals -- cattle, pigs, chickens, rabbits, turkeys and sheep -- in an intricate dance of symbiosis designed to allow each species, in Salatin's words, ''to fully express its physiological distinctiveness.''

What this means in practice is that Salatin's chickens live like chickens; his cows, like cows; pigs, pigs. As in nature, where birds tend to follow herbivores, once Salatin's cows have finished grazing a pasture, he moves them out and tows in his ''eggmobile,'' a portable chicken coop that houses several hundred laying hens -- roughly the natural size of a flock. The hens fan out over the pasture, eating the short grass and picking insect larvae out of the cowpats -- all the while spreading the cow manure and eliminating the farm's parasite problem. A diet of grubs and grass makes for exceptionally tasty eggs and contented chickens, and their nitrogenous manure feeds the pasture. A few weeks later, the chickens move out, and the sheep come in, dining on the lush new growth, as well as on the weed species (nettles, nightshade) that the cattle and chickens won't touch.

Meanwhile, the pigs are in the barn turning the compost. All winter long, while the cattle were indoors, Salatin layered their manure with straw, wood chips -- and corn. By March, this steaming compost layer cake stands three feet high, and the pigs, whose powerful snouts can sniff out and retrieve the fermented corn at the bottom, get to spend a few happy weeks rooting through the pile, aerating it as they work. All you can see of these pigs, intently nosing out the tasty alcoholic morsels, are their upturned pink hams and corkscrew tails churning the air. The finished compost will go to feed the grass; the grass, the cattle; the cattle, the chickens; and eventually all of these animals will feed us.

I thought a lot about vegetarianism and animal rights during the day I spent on Joel Salatin's extraordinary farm. So much of what I'd read, so much of what I'd accepted, looked very different from here. To many animal rightists, even Polyface Farm is a death camp. But to look at these animals is to see this for the sentimental conceit it is. In the same way that we can probably recognize animal suffering when we see it, animal happiness is unmistakable, too, and here I was seeing it in abundance.

For any animal, happiness seems to consist in the opportunity to express its creaturely character -- its essential pigness or wolfness or chickenness. Aristotle speaks of each creature's ''characteristic form of life.'' For domesticated species, the good life, if we can call it that, cannot be achieved apart from humans -- apart from our farms and, therefore, our meat eating. This, it seems to me, is where animal rightists betray a profound ignorance about the workings of nature. To think of domestication as a form of enslavement or even exploitation is to misconstrue the whole relationship, to project a human idea of power onto what is, in fact, an instance of mutualism between species. Domestication is an evolutionary, rather than a political, development. It is certainly not a regime humans imposed on animals some 10,000 years ago.

Rather, domestication happened when a small handful of especially opportunistic species discovered through Darwinian trial and error that they were more likely to survive and prosper in an alliance with humans than on their own. Humans provided the animals with food and protection, in exchange for which the animals provided the humans their milk and eggs and -- yes -- their flesh. Both parties were transformed by the relationship: animals grew tame and lost their ability to fend for themselves (evolution tends to edit out unneeded traits), and the humans gave up their hunter-gatherer ways for the settled life of agriculturists. (Humans changed biologically, too, evolving such new traits as a tolerance for lactose as adults.)

From the animals' point of view, the bargain with humanity has been a great success, at least until our own time. Cows, pigs, dogs, cats and chickens have thrived, while their wild ancestors have languished. (There are 10,000 wolves in North America, 50,000,000 dogs.) Nor does their loss of autonomy seem to trouble these creatures. It is wrong, the rightists say, to treat animals as ''means'' rather than ''ends,'' yet the happiness of a working animal like the dog consists precisely in serving as a ''means.'' Liberation is the last thing such a creature wants. To say of one of Joel Salatin's caged chickens that ''the life of freedom is to be preferred'' betrays an ignorance about chicken preferences -- which on this farm are heavily focused on not getting their heads bitten off by weasels.

But haven't these chickens simply traded one predator for another -- weasels for humans? True enough, and for the chickens this is probably not a bad deal. For brief as it is, the life expectancy of a farm animal would be considerably briefer in the world beyond the pasture fence or chicken coop. A sheep farmer told me that a bear will eat a lactating ewe alive, starting with her udders. ''As a rule,'' he explained, ''animals don't get 'good deaths' surrounded by their loved ones.''

The very existence of predation -- animals eating animals -- is the cause of much anguished hand-wringing in animal rights circles. ''It must be admitted,'' Singer writes, ''that the existence of carnivorous animals does pose one problem for the ethics of Animal Liberation, and that is whether we should do anything about it.'' Some animal rightists train their dogs and cats to become vegetarians. (Note: cats will require nutritional supplements to stay healthy.) Matthew Scully calls predation ''the intrinsic evil in nature's design . . . among the hardest of all things to fathom.'' Really? A deep Puritan streak pervades animal rights activists, an abiding discomfort not only with our animality, but with the animals' animality too.

However it may appear to us, predation is not a matter of morality or politics; it, also, is a matter of symbiosis. Hard as the wolf may be on the deer he eats, the herd depends on him for its well-being; without predators to cull the herd, deer overrun their habitat and starve. In many places, human hunters have taken over the predator's ecological role. Chickens also depend for their continued well-being on their human predators -- not individual chickens, but chickens as a species. The surest way to achieve the extinction of the chicken would be to grant chickens a ''right to life.''

Yet here's the rub: the animal rightist is not concerned with species, only individuals. Tom Regan, author of ''The Case for Animal Rights,'' bluntly asserts that because ''species are not individuals . . . the rights view does not recognize the moral rights of species to anything, including survival.'' Singer concurs, insisting that only sentient individuals have interests. But surely a species can have interests -- in its survival, say -- just as a nation or community or a corporation can. The animal rights movement's exclusive concern with individual animals makes perfect sense given its roots in a culture of liberal individualism, but does it make any sense in nature?

In 1611 Juan da Goma (aka Juan the Disoriented) made accidental landfall on Wrightson Island, a six-square-mile rock in the Indian Ocean. The island's sole distinction is as the only known home of the Arcania tree and the bird that nests in it, the Wrightson giant sea sparrow. Da Goma and his crew stayed a week, much of that time spent in a failed bid to recapture the ship's escaped goat -- who happened to be pregnant. Nearly four centuries later, Wrightson Island is home to 380 goats that have consumed virtually every scrap of vegetation in their reach. The youngest Arcania tree on the island is more than 300 years old, and only 52 sea sparrows remain. In the animal rights view, any one of those goats have at least as much right to life as the last Wrightson sparrow on earth, and the trees, because they are not sentient, warrant no moral consideration whatsoever. (In the mid-80's a British environmental group set out to shoot the goats, but was forced to cancel the expedition after the Mammal Liberation Front bombed its offices.)

The story of Wrightson Island (recounted by the biologist David Ehrenfeld in ''Beginning Again'') suggests at the very least that a human morality based on individual rights makes for an awkward fit when applied to the natural world. This should come as no surprise: morality is an artifact of human culture, devised to help us negotiate social relations. It's very good for that. But just as we recognize that nature doesn't provide an adequate guide for human social conduct, isn't it anthropocentric to assume that our moral system offers an adequate guide for nature? We may require a different set of ethics to guide our dealings with the natural world, one as well suited to the particular needs of plants and animals and habitats (where sentience counts for little) as rights suit us humans today.

To contemplate such questions from the vantage of a farm is to appreciate just how parochial and urban an ideology animals rights really is. It could thrive only in a world where people have lost contact with the natural world, where animals no longer pose a threat to us and human mastery of nature seems absolute. ''In our normal life,'' Singer writes, ''there is no serious clash of interests between human and nonhuman animals.'' Such a statement assumes a decidedly urbanized ''normal life,'' one that certainly no farmer would recognize.

The farmer would point out that even vegans have a ''serious clash of interests'' with other animals. The grain that the vegan eats is harvested with a combine that shreds field mice, while the farmer's tractor crushes woodchucks in their burrows, and his pesticides drop songbirds from the sky. Steve Davis, an animal scientist at Oregon State University, has estimated that if America were to adopt a strictly vegetarian diet, the total number of animals killed every year would actually increase, as animal pasture gave way to row crops. Davis contends that if our goal is to kill as few animals as possible, then people should eat the largest possible animal that can live on the least intensively cultivated land: grass-fed beef for everybody. It would appear that killing animals is unavoidable no matter what we choose to eat.

When I talked to Joel Salatin about the vegetarian utopia, he pointed out that it would also condemn him and his neighbors to importing their food from distant places, since the Shenandoah Valley receives too little rainfall to grow many row crops. Much the same would hold true where I live, in New England. We get plenty of rain, but the hilliness of the land has dictated an agriculture based on animals since the time of the Pilgrims. The world is full of places where the best, if not the only, way to obtain food from the land is by grazing animals on it -- especially ruminants, which alone can transform grass into protein and whose presence can actually improve the health of the land.

The vegetarian utopia would make us even more dependent than we already are on an industrialized national food chain. That food chain would in turn be even more dependent than it already is on fossil fuels and chemical fertilizer, since food would need to travel farther and manure would be in short supply. Indeed, it is doubtful that you can build a more sustainable agriculture without animals to cycle nutrients and support local food production. If our concern is for the health of nature -- rather than, say, the internal consistency of our moral code or the condition of our souls -- then eating animals may sometimes be the most ethical thing to do.

There is, too, the fact that we humans have been eating animals as long as we have lived on this earth. Humans may not need to eat meat in order to survive, yet doing so is part of our evolutionary heritage, reflected in the design of our teeth and the structure of our digestion. Eating meat helped make us what we are, in a social and biological sense. Under the pressure of the hunt, the human brain grew in size and complexity, and around the fire where the meat was cooked, human culture first flourished. Granting rights to animals may lift us up from the brutal world of predation, but it will entail the sacrifice of part of our identity -- our own animality.

Surely this is one of the odder paradoxes of animal rights doctrine. It asks us to recognize all that we share with animals and then demands that we act toward them in a most unanimalistic way. Whether or not this is a good idea, we should at least acknowledge that our desire to eat meat is not a trivial matter, no mere ''gastronomic preference.'' We might as well call sex -- also now technically unnecessary -- a mere ''recreational preference.'' Whatever else it is, our meat eating is something very deep indeed.

Are any of these good enough reasons to eat animals? I'm mindful of Ben Franklin's definition of the reasonable creature as one who can come up with reasons for whatever he wants to do. So I decided I would track down Peter Singer and ask him what he thought. In an e-mail message, I described Polyface and asked him about the implications for his position of the Good Farm -- one where animals got to live according to their nature and to all appearances did not suffer.

''I agree with you that it is better for these animals to have lived and died than not to have lived at all,'' Singer wrote back. Since the utilitarian is concerned exclusively with the sum of happiness and suffering and the slaughter of an animal that doesn't comprehend that death need not involve suffering, the Good Farm adds to the total of animal happiness, provided you replace the slaughtered animal with a new one. However, he added, this line of thinking doesn't obviate the wrongness of killing an animal that ''has a sense of its own existence over time and can have preferences for its own future.'' In other words, it's O.K. to eat the chicken, but he's not so sure about the pig. Yet, he wrote, ''I would not be sufficiently confident of my arguments to condemn someone who purchased meat from one of these farms.''

Singer went on to express serious doubts that such farms could be practical on a large scale, since the pressures of the marketplace will lead their owners to cut costs and corners at the expense of the animals. He suggested, too, that killing animals is not conducive to treating them with respect. Also, since humanely raised food will be more expensive, only the well-to-do can afford morally defensible animal protein. These are important considerations, but they don't alter my essential point: what's wrong with animal agriculture -- with eating animals -- is the practice, not the principle.

What this suggests to me is that people who care should be working not for animal rights but animal welfare -- to ensure that farm animals don't suffer and that their deaths are swift and painless. In fact, the decent-life-merciful-death line is how Jeremy Bentham justified his own meat eating. Yes, the philosophical father of animal rights was himself a carnivore. In a passage rather less frequently quoted by animal rightists, Bentham defended eating animals on the grounds that ''we are the better for it, and they are never the worse. . . . The death they suffer in our hands commonly is, and always may be, a speedier and, by that means, a less painful one than that which would await them in the inevitable course of nature.''

My guess is that Bentham never looked too closely at what happens in a slaughterhouse, but the argument suggests that, in theory at least, a utilitarian can justify the killing of humanely treated animals -- for meat or, presumably, for clothing. (Though leather and fur pose distinct moral problems. Leather is a byproduct of raising domestic animals for food, which can be done humanely. However, furs are usually made from wild animals that die brutal deaths -- usually in leg-hold traps -- and since most fur species aren't domesticated, raising them on farms isn't necessarily more humane.) But whether the issue is food or fur or hunting, what should concern us is the suffering, not the killing. All of which I was feeling pretty good about -- until I remembered that utilitarians can also justify killing retarded orphans. Killing just isn't the problem for them that it is for other people, including me.

During my visit to Polyface Farm, I asked Salatin where his animals were slaughtered. He does the chickens and rabbits right on the farm, and would do the cattle, pigs and sheep there too if only the U.S.D.A. would let him. Salatin showed me the open-air abattoir he built behind the farmhouse -- a sort of outdoor kitchen on a concrete slab, with stainless-steel sinks, scalding tanks, a feather-plucking machine and metal cones to hold the birds upside down while they're being bled. Processing chickens is not a pleasant job, but Salatin insists on doing it himself because he's convinced he can do it more humanely and cleanly than any processing plant. He slaughters every other Saturday through the summer. Anyone's welcome to watch.

I asked Salatin how he could bring himself to kill a chicken.

''People have a soul; animals don't,'' he said. ''It's a bedrock belief of mine.'' Salatin is a devout Christian. ''Unlike us, animals are not created in God's image, so when they die, they just die.''

The notion that only in modern times have people grown uneasy about killing animals is a flattering conceit. Taking a life is momentous, and people have been working to justify the slaughter of animals for thousands of years. Religion and especially ritual has played a crucial part in helping us reckon the moral costs. Native Americans and other hunter-gathers would give thanks to their prey for giving up its life so the eater might live (sort of like saying grace). Many cultures have offered sacrificial animals to the gods, perhaps as a way to convince themselves that it was the gods' desires that demanded the slaughter, not their own. In ancient Greece, the priests responsible for the slaughter (priests! -- now we entrust the job to minimum-wage workers) would sprinkle holy water on the sacrificial animal's brow. The beast would promptly shake its head, and this was taken as a sign of assent. Slaughter doesn't necessarily preclude respect. For all these people, it was the ceremony that allowed them to look, then to eat.

Apart from a few surviving religious practices, we no longer have any rituals governing the slaughter or eating of animals, which perhaps helps to explain why we find ourselves where we do, feeling that our only choice is to either look away or give up meat. Frank Perdue is happy to serve the first customer; Peter Singer, the second.

Until my visit to Polyface Farm, I had assumed these were the only two options. But on Salatin's farm, the eye contact between people and animals whose loss John Berger mourned is still a fact of life -- and of death, for neither the lives nor the deaths of these animals have been secreted behind steel walls. ''Food with a face,'' Salatin likes to call what he's selling, a slogan that probably scares off some customers. People see very different things when they look into the eyes of a pig or a chicken or a steer -- a being without a soul, a ''subject of a life'' entitled to rights, a link in a food chain, a vessel for pain and pleasure, a tasty lunch. But figuring out what we do think, and what we can eat, might begin with the looking.

We certainly won't philosophize our way to an answer. Salatin told me the story of a man who showed up at the farm one Saturday morning. When Salatin noticed a PETA bumper sticker on the man's car, he figured he was in for it. But the man had a different agenda. He explained that after 16 years as a vegetarian, he had decided that the only way he could ever eat meat again was if he killed the animal himself. He had come to look.

''Ten minutes later we were in the processing shed with a chicken,'' Salatin recalled. ''He slit the bird's throat and watched it die. He saw that the animal did not look at him accusingly, didn't do a Disney double take. The animal had been treated with respect when it was alive, and he saw that it could also have a respectful death -- that it wasn't being treated as a pile of protoplasm.''

Salatin's open-air abattoir is a morally powerful idea. Someone slaughtering a chicken in a place where he can be watched is apt to do it scrupulously, with consideration for the animal as well as for the eater. This is going to sound quixotic, but maybe all we need to do to redeem industrial animal agriculture in this country is to pass a law requiring that the steel and concrete walls of the CAFO's and slaughterhouses be replaced with . . . glass. If there's any new ''right'' we need to establish, maybe it's this one: the right to look.

No doubt the sight of some of these places would turn many people into vegetarians. Many others would look elsewhere for their meat, to farmers like Salatin. There are more of them than I would have imagined. Despite the relentless consolidation of the American meat industry, there has been a revival of small farms where animals still live their ''characteristic form of life.'' I'm thinking of the ranches where cattle still spend their lives on grass, the poultry farms where chickens still go outside and the hog farms where pigs live as they did 50 years ago -- in contact with the sun, the earth and the gaze of a farmer.

For my own part, I've discovered that if you're willing to make the effort, it's entirely possible to limit the meat you eat to nonindustrial animals. I'm tempted to think that we need a new dietary category, to go with the vegan and lactovegetarian and piscatorian. I don't have a catchy name for it yet (humanocarnivore?), but this is the only sort of meat eating I feel comfortable with these days. I've become the sort of shopper who looks for labels indicating that his meat and eggs have been humanely grown (the American Humane Association's new ''Free Farmed'' label seems to be catching on), who visits the farms where his chicken and pork come from and who asks kinky-sounding questions about touring slaughterhouses. I've actually found a couple of small processing plants willing to let a customer onto the kill floor, including one, in Cannon Falls, Minn., with a glass abattoir.

The industrialization -- and dehumanization -- of American animal farming is a relatively new, evitable and local phenomenon: no other country raises and slaughters its food animals quite as intensively or as brutally as we do. Were the walls of our meat industry to become transparent, literally or even figuratively, we would not long continue to do it this way. Tail-docking and sow crates and beak-clipping would disappear overnight, and the days of slaughtering 400 head of cattle an hour would come to an end. For who could stand the sight? Yes, meat would get more expensive. We'd probably eat less of it, too, but maybe when we did eat animals, we'd eat them with the consciousness, ceremony and respect they deserve.