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Reducing the pain, distress and anxiety that is sometimes generated by scientific work on animals is probably the issue that exercises the public most. Fortunately, it is one that is tractable, without bringing scientific work on animals to a halt, if only people are willing to talk to each other.

Critics of science believe that it is easy to tell when an animal suffers; some scientists believe it is impossible to know. I think that it is possible, but that the process of finding out is quite complicated. Even among humans, pain thresholds vary greatly from individual to individual and from one moment to the next. Nevertheless, there is a useful approach to uncovering whether animals might experience pain: it is to use the observable signs associated with the subjective sense of pain in humans as criteria for the assessment of pain in other animals .

Adopting a human-centred approach means asking whether the animal has anatomical, physiological and biochemical mechanisms similar to those that in a human are known to be correlated with such experiences. The approach also has to consider whether the animal behaves in similar ways to humans who are believed to be in pain.

No single criterion provides an all-or-none test for the existence of a subjective sense of pain. The evidence needs to be considered as a whole in order to build up a useful picture of the animal’s capabilities. And even though the laws about the use of animals in research tend to insist on precision, nobody can provide a cutoff point that is anything other than arbitrary. The fuzziness of the boundary between pain and the absence of pain becomes obvious as, one by one, the criteria for recognising pain cease to apply as simpler animals are considered. The same is true for stress and anxiety.

The best we can do is to provide criteria that are based on measurements of an animal’s behaviour and analysis of the way its nervous system works. If an animal subjected to conditions that might be supposed to produce pain stops activities that it habitually performs, or if it learns how to avoid such conditions, there are grounds for worrying that it might feel something. The existence of parts of its nervous system dedicated to avoidance of damage is another worry. These concerns are made much more acute if the animal has a large brain relative to its body and shows some of the cognitive capacity seen in humans.

Some four years ago, the Institute of Medical Ethics set up a working party, of which I was a member. The group debated the issues surrounding animal experiments for three years, and published its report last year. Applying this general approach to pain, stress and anxiety, the working party suggested that all vertebrates may be capable of experiencing some suffering, but that most invertebrates are not. For instance, insects have a complex nervous system, but apparently have no fibre system equivalent to the pain fibres of the vertebrates. Yet the cephalopods, a group of invertebrates that includes the octopus and squid, have much more complex nervous systems and behaviour. They probably can experience pain in some form, and so probably deserve special protection. At the moment, only vertebrate animals used in experiments are protected under the Animals (Scientific Procedures) Act of 1986.

Less ‘rational’ considerations also play a part in ethical decisions about animals and experimentation. It often remains a matter of taste where projection and empathy stop. The law governing the use of animals in research in Britain has clearly recognised that fact by giving special protection to dogs, cats and the horse family, the animals with which people identify most closely. But the way humans readily project their emotions and intentions into some animals and not others is itself a cause for concern. Few people have much fellow feeling for fish even though many fish are long-lived, have complicated nervous systems and are capable of learning complicated tasks.

So uncritical projections of human emotions and experiences onto animals, or the withholding of such empathy, can lead to a misreading of an animal’s suffering. The subjective experiences of an animal, if it has any, may be totally different from our own, reflecting its different way of life and the different ways in which its body works. Interpretation of what is observed in another animal should not be based only on extrapolations from humans but also on a good knowledge of its natural history and behaviour. Different species react differently to potentially damaging situations. Stimuli that make a human run and scream might make other animals, such as rats or cattle or horses, immobile. To most people, they do not look frightened, because alarmed humans would not normally behave like this.

With knowledge of how animals behave, there are often grounds for broadening rather than narrowing the range of animals that are believed to suffer. The plausibility of projections from human experience to other animals depends on good observational data about their normal behaviour, their requirements, their vulnerability to damage and the conditions in which they live. For instance, a horse with a broken leg may continue to graze. This makes good sense: it must maintain a high input of plant material to get enough to eat. Moreover, overt displays of pain may be counterproductive for an animal vulnerable to predators.

But it is worth emphasising that those who are opposed to the use of animals in research are not simply worried about animal suffering. For instance, many people are disturbed by the killing of an animal whether or not suffering is involved. Their ethical position is sometimes based on a sense of justice and a projection of rights from people to animals. However, it sometimes springs from a view about the connections between all forms of life, often generalised to include inanimate environments such as mountainsides and wetlands. Sometimes it is a reaction to the destruction of anything beautiful and extends readily to trees, works of art and architecture.

A quite different ethical concern is that treatment of animals is important because of the way it affects attitudes to fellow human beings. In this view, people who are cruel to animals may go on to behave similarly towards other people. Even people who are sceptical about consciousness in animals other than humans may argue that individuals who go against the fundamental human readiness to empathise with other animals may do the same to humans. A separate strand to this human-orientated approach is to respect the views of those who care deeply about animals. One person should not do anything that causes offence to others despite doubts about their reasons for being offended. These ethical issues are not ones that usually enter into discussions about what animals might feel, but they provide much fuel for burning passions.

All the same, assessments of animal suffering form a key part of the balancing act that is central to the law that regulates animal experiments in Britain. I argue that it is possible to reconcile a strong moral commitment to understanding biology and benefiting from such understanding by using scientific methods with an equally strong moral desire to minimise animal suffering.

Six years ago in New ÐÓ°ÉÔ­´´ (‘When to experiment on animals’, 20 February 1986), I proposed a ‘decision cube’ as a way of bringing together the various judgments that should be made about research on animals (see Figure). The cube had three separate dimensions: the scientific quality of the research, the probability of human benefit and the likelihood of animal suffering. I argued that animal suffering should be tolerated only when both research quality and probability of benefit were high. Moreover, certain levels of animal suffering would be unacceptable regardless of the quality of the research or its probable benefit. The decision rules used in this model would permit research of high quality involving little or no animal suffering even if the work had no obvious potential benefit to humans. This would enable scientists to work to understand phenomena even where they foresaw no immediate and obvious practical benefit.

The decision cube, which is sometimes denigrated as utilitarian, is emphatically not a cost-benefit exercise because it does not depend on a common currency or on the balancing of incommensurable properties. It is a set of rules that can be helpful in determining whether or not a particular piece of research should be done. I did not imagine that the boundary between going ahead with a research project or not doing so would be static. Indeed, all the evidence suggests that the consensus has been moving as shown in the figure, so reducing the animal suffering acceptable at a given level of ‘benefit’.

While the principle is straightforward, the practice of assessing likely value and harm is less so . Any judgment of the benefits of research turns on the likely contributions of a project to human understanding and education, as well as to human and veterinary medicine, the economy and the environment. Plausible assessments of the suffering that animals may experience can be based on how the animals were obtained, housed and treated experimentally and on how likely they are to experience in a human-like way changes to their environment and damage to their bodies. Understanding the animals requires projections from the behaviour and nervous system of humans combined with good knowledge of the natural history and behaviour of the animals in question.

The ultimate judgment, after these assessments have been put together, depends on the quality of the benefits and the severity of the costs. The aim of the whole process is to encourage scientific research with maximum benefit and minimum suffering to the animals. None of this is easy, but a lot of fair-minded people, starting from utterly different moral positions, are finding ways of reaching agreement. For this reason, I believe that the dark age of intolerance will not last for ever.

Patrick Bateson (FRS) is professor of ethology at the University of Cambridge and Provost of King’s College. He was a member of the Institute of Medical Ethics working party on animal experiments, which has recently published its report, Lives in the Balance, edited by Jane Smith and Kenneth Boyd, 1991, Oxford University Press.

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1: What it takes to suffer like a human

In 1987, under the auspices of the Institute of Medical Ethics, 18 people began meeting regularly to try to come up with some consensus about the rights and wrongs of experiments on animals. The group, which met for three years, contained campaigners for animal welfare, philosophers and lawyers as well as scientists from industry or academia. The working party’s report, published last year, spells out criteria by which policy-makers can judge both animal suffering and the value of a particular piece of proposed research.

The IME working party decided that an animal can feel pain if it meets the following criteria:

Receptors sensitive to noxious stimuli are present in functionally useful positions on or in the body.

Brain contains structures analogous to the human cerebral cortex.

Nervous pathways link receptors sensitive to noxious events and the higher brain.

Receptors in the central nervous system, especially the brain, are activated by opioid substances, implicated in pain control.

Painkillers modify the response to noxious stimuli and are chosen by an animal given access to them when the experience is unavoidable.

The animal responds to noxious stimuli by avoiding them or by minimising the damage to its body.

The animal’s avoidance of noxious stimuli is relatively inelastic. The response is largely unchanged irrespective of how much the animal is rewarded for a particular behaviour.

The animal’s response to noxious stimuli persists and it learns how to associate neutral events with noxious stimuli.

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2: The balancing act – how to judge the pros and cons of animal research

The working party of the Institute of Medical Ethics agreed that research could harm animals in many different ways, all of which decision-makers must take into account before approving any project.

Weighing up the harm to animals

What is an animal’s capacity to experience events that might damage it or shorten its life?

How damaging are the scientific procedures likely to be?

How adequate are the facilities for housing the animal?

What is the animal’s response to being kept in laboratory conditions?

How adequate are the facilities for recognising sickness and suffering in the animals and for dealing with them if they do arise?

Is the experiment designed to minimise the number of animals that will be used?

If it is taken from the wild, what is the animal’s response to capture, transport and quarantine and acclimatisation?

What is the effect on the wild population of its removal?

Weighing up the benefits of research

To judge the probable benefits of research, policy-makers must weigh up the proposed project’s likely contribution to:

The improvement of health and welfare in humans or other animals.

Science, in terms of its originality, timeliness and likely effect on understanding.

Education and training.

Employment and the economy.

The conservation of natural resources or to the reduction of the impact of humans on the environment.