Many very complex biological systems such as nervous and immune systems follow the same basic organisation and function in all animals. That means that even simple animals can be used to study these systems. A lot of what we know about brain cells (neurons) comes from studying the giant squid, for example, and microscopic nematode worms have helped in our understanding of brain diseases such as Alzheimer’s which causes dementia.  The law says that wherever a simpler animal can be used, whether it’s a squid, worm or fruit fly, it must be.

From animal models we have learned how many diseases work, how the immune system responds, why some people are more vulnerable than others and what we can do to fight back.

Recent advances in genetic technology have allowed the development of transgenic animals, which have new genes inserted into their DNA, allowing them to develop human diseases which do not naturally affect them. This has allowed researchers to create many animal models of human diseases which were previously difficult to study, usually using mice.

Animal models also help researchers to experiment with new kinds of therapy in ways which would be impossible in humans. New therapies for people with serious spinal injuries, for example, may be modelled on rats which have been surgically prepared. These surgeries are always carried out with anaesthetic and pain control medication to minimise any discomfort to the animal.

Sometimes it is the differences between animals and humans rather than the similarities that matter. The fact that other mammals are less susceptible to certain human diseases might give us a clue as to why the disease occurs, if we can locate a difference in the expression of particular genes, for example.

It is not just medicines that need to be tested to make sure they are safe. Diagnostic tools such as scanners, and implants such as heart pacemakers or artificial hips, are safe and effective only because they were developed and tested in animals. Many surgical techniques, such as open heart surgery and heart transplants, rely on methods and equipment that were developed using animals.

The animal tests provide data on efficacy and safety. They not only identify potential safety concerns, but also determine the doses which will be given to volunteers and patients during the first human trials.

Testing on animals also serves to protect consumers, workers and the environment from the harmful effects of chemicals. All chemicals for commercial or personal use must be tested so that their effect on the people and animals exposed to them is understood. The chemicals that we use day-to-day can accumulate in the water, ground or air around us, and their potential impact on the environment must be researched thoroughly.