The evolutionary history of rats has more holes than Swiss cheese, but researchers are trying to close them

Rats and humans have lived together for thousands of years. However, written historical records of rats migrating alongside people are sparse and some are entangled with myth and folklore.

Researchers at Drexel University, who are working to gain a better understanding of the evolutionary history of wild and domestic brown rats (Rattus norvegicus), recently presented a review of research on domestication events and genomic studies in the journal Science. The piece brings together findings about how rats moved from one place to another, particularly in association with humans.

Led by Jason Munshi-South, Ph.D., Betz Chair and professor in the College of Arts and Sciences, researchers scoured written records, archaeological remains and genomic data to bring together what we know about the evolutionary history of rats.

“We’re trying to understand how rats travel with humans and how, along the way, they have changed because of the types of environments humans have created,” said Munshi-South.

Using recent discoveries about the evolutionary history of brown rats and advances in zooarchaeology and population genomics, the research team anticipates new inquiries in the field will help to answer questions about the evolution of human migrations, trade corridors and economies of various societies—using rats as a proxy to understand what humans were doing in various places and times throughout history.

One example of a waypoint in this evolutionary history happened in Philadelphia in 1892, when Wistar Institute became one of the first biomedical research institutions to take wild rats from the streets and begin breeding them for laboratory research. Laboratory strains of rats, still used for biomedical models across the United States, can be traced back to Wistar.

According to the Drexel researchers, thousands of high-quality whole genomes from ancient and contemporary wild rats, as well as lab strains, will be sequenced in the next decade, thanks to advances in technology and a growing research focus on rats.

These resources, coupled with analytical advances, should vastly improve the understanding of the movement of brown rats around the world, their adaptations to diverse environmental conditions—particularly cities and other human-dominated contexts—and of the novel functional variation that will likely improve the utility of rats as biomedical models.

“The mindset of people about rats, typically, is that they’re pests. But now, people are reconsidering them as something important in evolutionary history—an organism that we should care about for other reasons,” said Munshi-South.