RenÄ Descartes was a genius, the possessor of one of the greatest minds of the 17th century; one of the greatest minds in all history. Three-hundred-and-forty years after his death, his philosophical achievements still merit six whole pages in the "Encyclopaedia Britannica".
Almost everyone who lived at the time of Descartes was more stupid than he was. And yet, there was an elementary truth which even the dimmest child of the dimmest scullion then knew, and which RenÄ Descartes could never admit. His huge mental power was devoted to the construction of a densely-argued theory which demonstrated, to the satisfaction of all the leading scholars of his day, that animals had no conscious life.
To have a conscious life you needed an immortal soul, and animals had no immortal soul. They believed nothing, desired nothing, felt nothing. They were like machines. If you fed in a stimulus, out would come the appropriate programmed response. If you stuck a knife into one, the squealing noise it made was purely mechanistic, not an expression of pain. Animals, lacking consciousness, could not feel pain, and anyone who thought otherwise was guilty of anthropomorphism.
What the scullion's child knew with equal conviction was that if you wounded an animal it suffered agony. Children everywhere still know this, and so at last do philosophers.
The word "vivisection", reduced by modern usage to mean any scientific procedure involving a live animal, was an aptly dreadful term for the way things used to be. If an anatomist wanted to consult the innards of a dog, he simply nailed it up by its paws and opened it with a knife. He wasn't wilfully cruel; simply misled by Cartesian logic into believing the question of pain did not arise.
Now we know differently. The question of subjective experience in non-human animals is a complex one, and still a very long way short of definitive resolution. The mental life of an animal is impossible to imagine, and difficult to investigate scientifically. But this much is certain: all vertebrate species, with central nervous systems like our own, feel pain when injured, and suffer when they are sick.
More controversially, all mammalian species which have been systematically studied by animal behaviourists indicate at least some ability to suffer mentally as well as physically. Animals do have beliefs and desires; they do suffer boredom, grief, loneliness; and, like human prisoners or torture victims, they can be driven to madness by prolonged abuse. But there is, of course, a very grave danger in making comparisons of this sort. Human desires are very different from animal desires, and animal desires vary greatly from species to species. It is no use a welfare campaigner saying: I wouldn't fancy living in the way a tapeworm does, therefore life inside an intestine is patently cruel. Anthropomorphically projecting human tastes on to other species is the route that leads to the exquisite suffering of the chocolate-fed lap-dog, or the chimpanzee in fancy dress.
There is a phrase in common usage among animal behaviourists - "critical anthropomorphism" - which is a useful one to keep in mind. What it suggests is that anthropomorphism is fine, so long as you critically adjust your imaginative projection to accord with the known characteristics of the animal. For example: if the animal in question is a bat, and you know that its preferred lifestyle is to hang upside down in a dark, insect-infected cave, then you can reasonably suspect that it might be cruel to keep it upright in a greenhouse. This is the basis of almost all current behavioural research programmes: to determine what the animals' own preferences really are.
This is not as absurd as it sounds. Consider once again the battery hen. A government report in 1965 pronounced strong disquiet about the cheesewire-thin, hexagonal wire-mesh used as flooring in the birds' cages. It felt this must cause extreme discomfort, and wanted it replaced with thicker, rectangular mesh.
But what did the hens themselves think? Researchers set up a simple experiment in which the birds were introduced to a variety of different floor surfaces, then given the freedom to stand on whichever one they liked. The vote was overwhelmingly in favour of the original fine-gauge hexagonal mesh, and the highly-distinguished and eminently well-qualified members of the human committee had to suffer the mild indignity of being over-ruled by a bunch of chickens. This shows two things: first, the danger of making even well-meaning assumptions; second, the value of multiple choice tests in helping to define an animal's real welfare needs. By similar methods scientists can establish some basic preferences about, for example, cage design, group size and diet. By introducing some physical obstacles and performance tasks into the experiment, researchers can also see how hard the birds are prepared to "work" to achieve each particular benefit - eg hardly at all for minor variations in diet, but very hard indeed for the right to forage. In this way one establishes a genuinely hen-based scale of values, distinguishing the necessities in its life - the things it is prepared to work for - from the luxuries which it will accept only if offered on a plate.
Again, however, there are dangers. If, for example, a pigeon demonstrated through a choice test that its favourite food was Mars bars, it wouldn't prove the cruelty of feeding it peas. Similarly, if you offered it a choice between perching on a red-hot poker and a razor blade, it would not prove that the razor blade was its idea of a perfect place to roost. All you can be sure of is that an animal will choose the least distressing option within its available range of choice.
What, therefore, is a commonsense definition of animal suffering? Marian Dawkins, a senior lecturer in ethology at Oxford University and author of the best-known book on the subject, "Animal Suffering" (Chapman & Hall, ú7.95), says this: "To know whether an animal is suffering, it is necessary to answer only one question. Is it motivated to do something it is prevented from doing?"
This is not to say that all kinds of suffering are equal or even undesirable. A Rottweiler might be motivated to bite a hole in the postman: restraining it from doing so might cause it to suffer momentary feelings of frustration, but would not fall within most people's commonsense definition of cruelty. If, however, it were to be denied food when motivated to eat, or kept chained in a kennel too small to let it stand up when motivated to take exercise, then the cruelty is obvious.
The results of behavioural deprivation are seen most notoriously in zoo animals: the relentlessly pacing polar bear, the tiger that chews the bars of its cage, the masturbating chimpanzee. All these are symptoms of stress which can derive from a variety of causes: loneliness, for example, when a social animal is kept in isolation from others of its kind, lack of opportunity for sexual release, or simple boredom. But if it is the polar bear that makes the headlines, it is down on the farm, away from public gaze behind the closed doors of the intensive pig-unit or in the battery house, that the toughest questions still have to be asked.
One of the commonest methods of assessing the natural requirements of a domesticated animal is to look at its closest wild ancestor. In the case of the chicken, this is the wild red junglefowl of south-east Asia - a species which lives in small flocks, is able to fly and roost in trees, and whose hens build individual nests in seclusion to rear their chicks. But none of these fundamental behaviour patterns is available to the caged battery hen, so it must suffer agonies of frustrated rage. Or so we may be tempted to conclude.
The problem is that the selective breeding of the domestic chicken has been going on for at least 4,000 years (7,000 years in pigs), and the modern battery hen is as different from a red junglefowl as Cyril Smith is from a Palaeolithic hunter-gatherer. What can be learned from comparing a lightweight, fleet-footed, fully-flighted bird, laying perhaps 50 eggs a year and rearing young, with a sedentary, flightless battery hen laying nearly four times as many eggs and selectively bred never to go broody? Or, perhaps even more grotesque, with a heavyweight broiler bird, so overloaded with meat that often it cannot even stand up?
"What we have to consider," says Marian Dawkins, "is that some animals are now so altered by years of human interference that their 'natural' environments are no longer the jungles or plains of their ancestors. Neat and tidy comparisons with wild animals are simply not possible any more. There is no longer any such thing as THE pig or THE chicken."
This raises two important questions. Can selective breeding itself produce results which are cruel? And what are the "natural" requirements of a genetically manipulated animal?
Common sense provides the answer to the first. One clear example is the suffering imposed upon dogs by breeders in pursuit of show points. An animal which cannot breathe comfortably, or which cannot see, or which suffers arthritis or hip dislocation as a result of cosmetic adjustments to its physiology, is obviously suffering. The suffering is obviously needless, and by any sensible test the wilful imposition of avoidable suffering is cruel. With this much most people outside the dog-show circuit would probably agree.
But what about the broiler chicken that collapses under the pressure of its own accelerated growth-rate? Or the turkey which has to be artificially inseminated because it is too fat to mate? Or the Belgian Blue cow that is so heavily muscled, and produces such heavy calves, that it cannot give birth naturally and has to be delivered by Caesarian section? Or the dairy cow which has to waddle to the milking parlour with the weight of eight gallons of liquid between its hind legs - 16 times more than it would naturally produce to feed a single calf, imposing a metabolic workrate which burns the animal out and sends it to the slaughter-house after only four years of productive life? And what about the transgenic laboratory mouse guaranteed to develop cancer within 90 days of birth?
Unlike the snuffling bulldog or rage-maddened Rottweiler, all these examples merit at least some consideration on the human-benefit side of the cost-benefit equation: cheaper meat and milk, more efficient cancer-research. Like the bulldog, however, all these animals do undoubtedly suffer increased stress as a result of interference with their physiology. How far such developments should be allowed to proceed is one of the most difficult problems welfare organisations and legislators will have to address.
In the meantime it remains to be resolved what the "natural" behaviour of such animals is really like. Science is doing its best with multiple-choice tests, physiological stress measurements, photographic surveys of chickens' wing-stretching habits, painstaking comparisons of one kind of pig-pen with another. But in the end, as the scientists themselves acknowledge, it all comes back to common sense, to a question of simple humanity. The schoolchild knows as well as anyone that there are basic, bedrock elements in the behaviour of all animals - the urge to eat, drink, sleep, associate with others, move and stretch their limbs - that are irreducible.
By denying them we make a conscious decision to impose suffering. There are many who believe that a reborn Descartes, armed with modern scientific knowledge, would be a vegetarian.
