Why Are Mice Used in Research — and Not Other Animals?

In almost every movie involving a scene with a laboratory, mice are often squealing in the background. Even in scientific literature mice are showing up in studies covering all sorts of diseases. But why? Of course we wouldn’t want to use human beings as test subjects, but why mice and not guinea pigs — or any other animal for that matter? 

Interestingly enough, there are quite a few reasons why mice are often used in scientific research.

The practical reasons

Beyond genetics, mice have a lot of features that make them practical for laboratory research. They're small, which means they require less space and are relatively inexpensive to house and care for. They reproduce quickly (a mouse reaches sexual maturity in about six weeks and can have a litter every three weeks), meaning researchers can study multiple generations in a short time frame. Their short lifespan (about two years) also allows scientists to observe aging-related diseases in a compressed time period.

Mice are also highly amenable to genetic engineering. Scientists have developed techniques to "knock out" specific genes in mice, add human genes to their genome, or create mice that are engineered to develop particular diseases. These "transgenic" and "knockout" mouse models have been revolutionary for understanding how specific genes contribute to disease.

What about other animals?

Other animals are used in research too, depending on the question being asked. Rats are frequently used in neuroscience and behavioral research because their brains are larger and more complex than mice, making them better models for certain cognitive studies. Zebrafish are popular in developmental biology because their embryos are transparent, which means you can watch organs form in real time under a microscope. Fruit flies, too, have been critical to genetics research for over a century. Non-human primates like monkeys are used in some studies, particularly for neurological research, though their use is much more restricted due to ethical concerns.

Dogs, cats, and larger animals do appear in some research contexts, particularly in veterinary medicine or for testing devices like pacemakers, but they're used far less frequently than rodents, and their use is subject to strict ethical guidelines.

The ethics

It is widely understood that the use of animals in research is ethically complex. Scientists work under a framework called the "Three Rs”: Replace (use alternatives where possible), Reduce (use the minimum number of animals necessary), and Refine (minimize suffering and improve welfare). These principles are the foundation for how animal research is designed and approved.

The conversation around animal research is ongoing. Developments in computer modeling are providing attractive alternatives that can reduce the need for live animals. However, these advances are not happening at a rate where we can completely stop using mice for our experiments. So for now, mice will continue to be a cornerstone of biological research.