In 1957, the Russian geneticist Dmitry K. Belyaev had a plan. He wanted to see whether he could duplicate the domestication of dogs in another species. It had taken humans thousands of years to tame dogs through selective breeding. Could Belyaev accomplish the same thing with foxes in a single human lifetime?
He went to Siberia, rounded up some silver foxes bred for the fur trade and began the experiment. Every time a litter was born, he would subject the little fox kits to a standard test of tameness. The calmest, gentlest kits were selected and the rest killed. After 25 years and 20 generations of foxes, the experiment succeeded in breeding foxes that were tame enough to be pets. Interestingly, as the foxes became tamer, their tails shortened and began to curl, their ears got floppier and their coats became spottier. This parallel shift in physical traits along with behavioral traits is known as domestication syndrome, and investigating that process has led to insights into evolutionary development [source: Newman and Craig].
The silver fox experiment is an example of animal testing used in behavioral research. Pavlov's famous dogs fall under this category as well. But these are just a few instances of the manifold ways in which scientists use animals to help them answer a wide range of questions.
Much research in the field of evolutionary biology is conducted using fruit flies and tiny nematode worms, thanks to their rapid rates of reproduction and ease of breeding. Researchers sometimes use nematodes like C. elegans, for instance, to identify an effective antibiotic by infecting a group of worms with a disease, then exposing a control group to a potential antibiotic to see who survives [source: AnimalResearch.Info].
In the area of disease research, it all depends on which animals are susceptible to what. Armadillos, for instance, are the only creatures other than humans known to suffer from leprosy, also known as Hansen's disease. Just like Goldilocks' favorite porridge, their body temperature is justright to allow them to harbor the M. leprae bacteria. As a result, scientists used those armored critters to better understand leprosy and create an experimental vaccine [source: AnimalResearch.Info].
Famously, rats are common denizens of laboratories, but mice are even more ubiquitous thanks to the fact that their genes and ours overlap by a whopping 90 percent, not to mention the fact that their cell structure and organ organization are essentially the same as ours. Much of the research conducted with mice consists of breeding and genetic modification together with behavioral experiments, which often involve memory tests and mazes.
Cats are typically used for neurological research into diseases, treatments and general function because of their highly developed senses of hearing, sight and balance. Dogs, especially the docile beagle, are the subjects of biomedical research into conditions like prostate cancer and muscular dystrophy since they are the only other species to share these diseases with us [source: AnimalResearch.Info]. They're also often the second step in the process of testing drugs for safety. In certain cases, after researchers try a drug out on mice, they'll proceed to dogs.
Then, of course, there are the non-human primates (mostly macaque monkeys because of their large and widely distributed population). While the number of experiments with primates have gone down drastically in recent decades (more on that later), neuroscientists looking into brain diseases such as Alzheimer's still rely on them for advances in that field. That's because there are just no other animals that have brains as similar to humans as those distant, simian cousins [source: Oxford University].