The moral status of animals is at the centre of the debate about whether they should be used in research and testing. Few people disagree that animals count in our moral framework, but the question is how much?
The key issue has to be their ability to feel pain and other forms of suffering. The law regulating animal experiments operates on the understanding that animals have the capacity to experience "pain, distress, suffering or lasting harm".
That understanding is based on research proving that animals have pain receptors and specialised nerve fibres conveying signals to brain areas that interpret pain sensation. They also suffer associated emotional reactions to pain, such as distress and fear.
Medical research into human pain and its treatment is based on these shared experiences. Scientists devise rodent "models" of pain that include injecting formalin into their paws, damaging their nerves, burning them and giving them electric shocks. In developing therapies for human anxiety, fear, depression and panic, rats and mice are subjected to a variety of tests such as being deprived of water and then given electric shocks each time they try to drink.
The peer-reviewed literature details the effects of stress, anxiety and depression on animals. Just as we do, they experience sleep disturbances, a decline in immune function, loss of pleasure in daily activities, ulcers and changes in stress hormones, heart rate and blood pressure. Researchers state that these animal models replicate the pharmacology, physiology and symptomatology of human emotional states.
Even though human experimentation would advance medical progress more quickly, most of us adamantly oppose experiments on non-consenting people.
Why shouldn't the same argument apply to other animals?
Those who defend animal experiments say that all humans, regardless of cognitive state, lack of moral duties or incapacity to suffer, have a moral status that protects them from forcible experimentation. This includes those with advanced dementia, infants and patients in comas. But they assert that all other species should not enjoy similar protection.
It is claimed that we are special because we have the sophistication to think about ethics. But being able to read or vote is irrelevant to an individual's experience of pain and suffering, whether that individual is a human or some other animal. Questions about where the line is drawn, at ants, amoebae or spinach plants, miss the significance of sentience and suffering.
An instinctive species preference is no basis for a moral framework and reflects poorly on the much-quoted sophistication of the human mind. As a guide to how we should behave such prejudices fail miserably, as parallels with racism illustrate. A utilitarian approach - trying to achieve the greatest good for the greatest number - would mean having to accept forcible experiments on unwilling people for the wider benefit of the rest of the population. Either all sentient animals share a similar moral standing and experiments on them are wrong in principle, or we're free to choose who pays the price for medical progress. As history shows, some researchers will prefer human subjects.
Then there is the question of medical progress. Animal experiments have been a major strand of scientific endeavour for a very long time. But there have been few systematic reviews of their validity, which has usually been assumed rather than proven. There are many reasons why animal experiments may fail, such as species differences.
A government advisory committee recently said that although animal experiments can be scientifically valid, this "has to be judged case by case and subjected to detailed critical evaluation". Historically, this has not been the case, although the absence of evidence has not stopped defenders of vivisection from claiming that all major breakthroughs have depended on animal experiments. In fact, there is evidence that slow progress with stroke, multiple sclerosis, lung and bowel cancers, Alzheimer's disease, an Aids vaccine and septic shock can be attributed to faulty animal models.
In safety testing, many animals are poisoned, sometimes fatally. Yet the animal tests that have been evaluated have performed poorly. For example, a recent study of 150 novel drugs revealed that rodent data predicted fewer than half of the significant toxic effects seen in subsequent clinical trials. In another case involving rodent cancer tests, only 57 per cent of 121 chemicals tested gave the same results when the tests were repeated.
The poor performance of rodent cancer tests means that people are being exposed to carcinogenic chemicals while safe ones have been withdrawn.
It is morally repugnant that 40 million or more animals are exposed to pain, distress or suffering in the world's laboratories every year. It is even more appalling that a significant proportion of them pay with their lives for research without any medical benefit. It is time to rethink how we conduct medical research and explore better and more humane options.
Gill Langley is scientific adviser for the Dr Hadwen Trust for Humane Research.