The Evolution of the Rat

A study by University of California researchers in San Diego reports that humans, rats, and mice have a similar number of genes, though their genomic architecture differs markedly. Comparing these genomes provides insight into each species’ evolution; for example, the study suggests rodents have evolved more rapidly than primates.

Rats are adapted for efficient foraging and rapid reproduction, which helps populations rebound quickly. There is an increasing number in towns and cities worldwide despite significant spending on eradication. When control campaigns end, many rodent populations quickly recover—often called the “boomerang effect.”

Smelly Pipes

Rats rely heavily on smell for danger detection, territorial marking, and mate selection. A rat has roughly 2,070 odor receptors—about one-third more than a mouse—and more pheromone receptors. Rats also express detoxification genes that help the liver process toxins.

Wild rats commonly inhabit sewers and other malodorous environments, whereas mice more often occupy fields and wooded areas. That ecological split is reflected in their gene expression patterns. Some researchers propose that selectively “knocking out” certain genes could better align rodent detox pathways with human biology to improve toxicology and drug-safety testing.

Ancestral Core

Rattus norvegicus—misidentified in 1769 as a Norwegian import rather than native to Asia—has a genome of about 2.75 billion base pairs (vs. ~2.9 billion in humans and ~2.6 billion in mice). A global sequencing effort found the three species possess a comparable number of genes.

Sequence data indicate rat and mouse lineages diverged 12–24 million years ago. Roughly half of the chromosomal rearrangements between rat and primates occurred during that time window, with fewer changes on the primate side—supporting faster evolutionary change in rodents. Even so, all three species retain ~280 large, nearly identical chromosomal blocks—an “ancestral core” encompassing about a billion bases that appears essential.

Lethal Control Campaigns

Studying urban rat biology in the wild is challenging. To assess whether city rodents develop distinct traits, researchers have examined how lethal control affects rat genetics and behavior. In Brazil, for example, an aggressive 2015 eradication program reportedly halved the rat population but led to a ~90% drop in genetic diversity—a classic genetic bottleneck with increased inbreeding among survivors.

Such shifts can alter behavior and disease dynamics. Urban rats often consume highly processed foods rich in sugars, fats, and animal proteins, which may influence pathogen transmission potential.

Coordination Gaps & Long-Term Outcomes

In practice, cooperation between municipal pest-management teams and scientists is limited by short timelines and budgets. Meanwhile, repeated lethal programs can select for “fitter” rodents—individuals better at avoiding baits, traps, or toxins—who then pass those traits to offspring. Specific gene variants have been identified that reduce susceptibility to common rodenticides.

Conversely, severe and repeated bottlenecks can reduce genetic variation, which is crucial for adapting to changing environments. Over time, that could lead to declines in survival and reproduction (inbreeding depression)—but in the short term, selection can still favor the trap- and toxin-averse.

Practical Control: Traps & Integrated Measures

Because rodent populations can evolve around chemical controls, trapping remains one of the most practical, low-impact options—especially for those avoiding rodenticides. The A24 rat & mouse trap provides quick-kill, self-resetting performance suitable for ongoing control.

For best results, combine trapping with exclusion (seal entry points), sanitation (remove food and harborage), clutter reduction, and routine inspections—an integrated program focused on long-term, sustainable suppression.

Conclusion

Rodents have fueled past pandemics and remain vectors for numerous pathogens. Today, improved sanitation and targeted control reduce risk, but success still hinges on waste management, exclusion, and consistent, humane control methods. Explore our products and trapping guides to build an effective, sustainable program.