From formulating new cancer drugs to testing dietary supplements, mice and rats play a critical role in developing new medical wonders. In fact, 95 percent of all lab animals are mice and rats, according to the Foundation for Biomedical Research (FBR). Scientists and researchers rely on mice and rats for several reasons. One is convenience: rodents are small, easily housed and maintained, and adapt well to new surroundings. They also reproduce quickly and have a short lifespan of two to three years, so several generations of mice can be observed in a relatively short period of time. Mice and rats are also relatively inexpensive and can be bought in large quantities that breed rodents specifically for research. The rodents are also generally mild-tempered and docile, making them easy for researchers to handle, although some types of mice and rats can be more difficult to restrain than others. Most of the mice and rats used in medical trials are inbred so that, other than sex differences, they are almost identical genetically. This helps make the results of medical trials more uniform, according to the National Human Genome Research Institute. As a minimum requirement, mice used in experiments must be of the same purebred species. Another reason rodents are used as models in medical testing is that their genetic, biological and behavior characteristics closely resemble those of humans, and many symptoms of human conditions can be replicated in mice and rats. “Rats and mice are mammals that share many processes with humans and are appropriate for use to answer many research questions,” said Jenny Haliski, a representative for the National Institutes of Health (NIH) Office of Laboratory Animal Welfare.