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For over two millennia, scientists have dissected animals to unlock biological secrets. Today, roughly 5% of the animals used in medical research are fish, dogs, cats, invertebrates, and primates, while the remaining 95% are rodents. Every year, millions of mice, rats, hamsters, and guinea pigs are utilized worldwide. In pursuit of life‑saving therapies, cancer treatments, and surgical innovations, the advantages of animal testing often outweigh the ethical considerations.
When researchers employ mice in laboratory studies—known as “murine studies”—they are not seeking drugs for rodents, but for humans. Using rodents as proxies is ethically preferable to testing on humans directly. Mice reach sexual maturity in a few weeks, are prolific, and can be ethically managed in controlled environments. Their physiology and genetics are also strikingly similar to ours.
Laboratory mice belong to the domesticated subspecies Mus musculus domesticus. Although primates share even closer genetic similarities, the extensive research, behavioral understanding, and fully sequenced genome of the lab mouse make it the optimal model. Scientists can compare genetic changes directly, as lab mice share about 85% of functional DNA with humans, with the remaining 15% still closely related.
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Historically, mice were not always the first choice for scientific inquiry. Louis Pasteur, for example, conducted early germ‑theory experiments on dogs, cows, sheep, and primates. It was not until 1902 that Abbie Lathrop deliberately bred mice for laboratory use, paving the way for today’s domesticated strain. The 1980s, however, marked a dramatic surge in murine research with the advent of gene editing technologies.
Gene editing’s rise coincided with the Human Genome Project (HGP), a global effort that sequenced the entire human genome between 1990 and 2003. The HGP highlighted the near‑identical genetic architecture of mice and humans, revealing that only about 10 of the 4,000 genes lack direct counterparts.
With gene editing, scientists can create “knockout” mice—individuals in which a specific gene has been removed from the embryo. By comparing knockout mice to control groups, researchers gain deep insights into gene function and disease mechanisms, such as cancer. Though many lab mice are sacrificed in this process, their contributions have saved countless human lives.
