As a medical doctor and scientist, I have been aware of many animal experiments. Indeed, I have participated myself (under licence) in many experimental protocols. But i am starting to change my mind.
Animal testing is important because it will show us if new drugs might kill people rather than cure them. I understand the arguments here, and they are far too complicated to go into in this answer. I will just tell you my thoughts.
I love animals, I always did, which is why i did Zoology as a degree. I have seen them horribly abused in the name of "science". And I have yet to see evidence of the benefits of those experiments. I abhor those experiments that sacrificed animals to test cosmetics and cigarette smoke (the latter of which I have witnessed first hand).
But there is a point here. Is a mouse worth more than a human being? We kill them with traps, we allow our pet cats to kill them. We would never consider letting our pet cat (a tiger) kill a human. Anyway, if the death of a mouse can save one human being, I would not stand in front of the mother of that child and say that the life of a mouse was more important than that of her daughter.
I also believe there are new technologies that allow experimentation without animals. We should be focussing all our energies there.
A couple of points:
(1) Scientific data is gathered from experiments with living creatures because those products are going to be used on humans.
(2) Only so much research can be done prior to testing on living systems. Data gained can be used to see how products affect human body systems.
(3) Not all "animal testing" is harmful to the animal.
(4) Living systems sometimes react to new products in unexpected ways. It is the hope of most animal testers that the negative impacts of testing be reduced as much as possible before animal testing, and then another refinement before humans use the product.
Animal testing is very important for medical research. When scientists are trying to develop a new drug or a new treatment, it is necessary to find out if it will work in the right way. The scientists may *think* it will work, based on their theories, but they won't know for sure until they try it.
Of course, scientists can not test totally untried medicines or treatments on human beings. No human being would want to be a "guinea pig" for a treatment that has never been proven to work. Because they can't try the treatments and medicines on humans, scientists try them on animals since they are the next best thing.
Animal testing is used for many different kind of research, most of it being for medical research. The animal research is important for two reasons.
First, many different animals have different characteristics, that makes testing of some effects and phenomenon on some specific animals faster and more effective. In many instances it will not be possible to conduct such tests on human beings. For examples, some animals navigate in dark using sonar waves. There are other animals who are able to sense heat waves. Any experiments involving use of such senses cannot be performed with humans.
Second, by first conducting test on animals, it is possible to collect lot of valuable data without exposing humans to the risk of such testing. This does raise the question cruelty to animals. But that is another matter.