Living organisms are incredibly complex and scientists still only understand a very small fraction of the structures, chemicals, interactions and metabolic pathways in humans and animals. The only way for scientists to learn more about them is through organisms that possess these traits. That's why animal research is so important for the future of medicine and the ability to treat and cure diseases.
Anti-vivisectionists often claim that vivisection is 'junk science'. The benefits accruing from animal testing demonstrate that this is nonsense. Another claim is that they want to save medical science from the 'dark ages' by banning animal research and using alternatives instead.
Alternatives to animal testing do exist -- and scientists already use them. In fact, they are mandated to do so by law wherever possible. Licences to carry out animal testing are only granted by the UK's Home Secretary when a convincing case is made that the likely benefits to human beings outweigh any welfare loss to animals. Furthermore, animal testing is an incredibly costly process and needs to be minimised for economic reasons.
So what alternatives do exist? Tests are carried out using cells, DNA, proteins, and in-vitro techniques in the initial stages of biomedical research. It's only when a point is reached where no experimental model can be substituted for a living organism that animal testing is considered. For instance, no amount of testing on computer models or strings of cells can tell us what the likely effect of a drug will be on blood pressure - because neither of these things has a circulatory system, blood, heart, and so on. Likewise, we cannot predict how a drug might be metabolised without introducing it to an organism with a liver. We must therefore trial drugs on whole living organisms at some stage.
When working to learn new information in science, the process starts at the smallest level possible. This is often work done with DNA from cell lines or the proteins that cause disease. As scientists and researchers learn more about their topic, the level of complexity increases in the models they study. They may move on to bacterial cells, then mammalian (animal and human) cells, then into entire organs and eventually into animals. The principles of 'reduce, refine and replace' are not a revolutionary alternative to animal research - they represent what scientists already do.
Anti-vivisectionists sometimes claim that a computer programme has been invented which correctly simulates an entire human body, and that this could be used instead of animals. This is totally false - no such programme exists, and no computer powerful enough to create such a model exists either. Computer models of simple proteins are used in the early stages of medical research but, like all alternatives to full organisms, are strictly limited in their applications. We simply do not have the technological sophistication to replicate the incredibly intricate and sensitive machinery of even the simplest animal organisms, let alone the much more complex human body.
So asking why alternatives aren't used is a misleading question. The experiments used that aren't performed in animals are complementary to the experiments performed in animals and help researchers understand the big picture of a disease or system.If there are any methods that can be used before an animal to learn new information, British law dictates they must be used.
See also our blog entry on the 3Rs.