Keep pulling the thread on Northeast Asia.
The origin of brown rats is believed to be Northeast Asia, based on circumstantial evidence such as the presence of free-living populations not associated with human settlements, a phenomenon not typically seen elsewhere.
Genetic evidence suggests brown rats originated in Eastern Asia, as the species exhibits its greatest genetic diversity in that region.
A method called ZooMS (Zooarchaeology by Mass Spectrometry) provides a quick and inexpensive way to distinguish between the bones of brown rats and black rats.
The earliest known evidence of brown rats in North America comes from a merchant ship that sank in the year 1760.
Based on genetic analysis, it is estimated that brown rats dispersed from Northeast Asia to Southern China and Southeast Asia approximately 800 to 1,000 years ago.
Researchers believe that brown rats were introduced to North America through at least two separate dispersal processes.
Brown rats dispersed to the Pacific coast of North America via a route that was entirely independent of their introduction to the Atlantic coast.
Most brown rat populations were established from a single genetic lineage, suggesting an initial introduction event followed by a large population boom with few additional migrants being integrated.
Isotope analysis of brown rats indicates that urban populations tend to consume more meat and protein than their rural counterparts.
Research on brown rats in New York City has found that their skull shape has changed over time.
The speaker predicts that brown rats will become a larger and more important presence in cities in the future as a result of climate change.
Brown rats are likely continuing to evolve and adapt to urban conditions, partly because their presence in these environments is relatively recent.