Own pet rats? Rest easy. Your fingers are safe.
A recent study from the Max Planck Weizmann Center for Integrative Archaeology and Anthropology at the Max Planck Institute for Evolutionary Anthropology shows that domesticated rats selectively bred for tameness are highly unlikely to bite.
According to postdoctoral researcher Dr. Federico Becerra:
"We found that a strain of rats bred to be aggressive towards humans bit often and with lots of force, whereas a highly tame strain never bit at all. Furthermore, females from the aggressive strain were much more likely to bite and bit harder than males."
Becerra hypothesizes that differing hormonal responses to stress account for the differences in the biting behavior of males and females from the aggressive strain of rats. Stressed out male rats might bite strictly as a function of self-preservation. However, female rats might bite as a means of protecting their young.
In the study, researchers bred two strains of rats. They selectively bred one strain to be aggressive. They selectively bred another strain to be as tame as possible. They bred both strains for many generations, selecting the most tame and aggressive offspring from each respective strain's newest generation to continue the line.
Becerra explains, "We found that tame rats, both male and female, never bit humans in this study."
The researchers also cross-bred individuals from the tame and aggressive strains. They found that mixed females were more aggressive than mixed males. However, they found no difference in the level of tameness between males and females in the tame-only strain.
"So long as they are tame, pet rats of both sexes are equally safe for humans to keep as pets. However, even domesticated, these rats may still be aggressive toward each other," says Becerra.
This study casts new light on morphological and behavioral aspects of rat domestication. And while domesticated rats are a starting point, this kind of research will eventually help researchers understand the biological effects of domestication in other species.