City Raccoons' Shorter Snouts Could Be an Early Sign of Domestication

A new analysis led by Raffaela Lesch, an assistant professor at the University of Arkansas at Little Rock, suggests that raccoons living in U.S. cities may be showing one of the earliest physical signs associated with domestication: slightly shortened snouts. The finding — described by the lead author as a possible glimpse of domestication in its infancy — is intriguing but preliminary.

How the study was done

Lesch and a team of students reviewed more than 19,000 raccoon photos from iNaturalist, a public database of wildlife observations. From that pool they identified 249 images that displayed raccoons in clean profile and used imaging software to measure snout length (tip of the nose to the tear duct) and total head length (nose tip to the ear attachment).

Key result

When mapped by county, the measurements showed a consistent pattern: raccoons photographed in urban counties had snouts about 3.6% shorter on average than raccoons from rural counties. That change in snout length matches one element of what researchers call "domestication syndrome," a suite of traits often seen in domestic mammals.

“That doesn’t sound like a lot, and in a sense, it is not a lot, but if you think about these animals potentially only being at the very early beginning stages of domestication, that is still a fairly clear signal,”

Lesch said. The study was published October 2 in the journal Frontiers in Zoology, with Lesch as lead author.

Context and caveats

Charles Darwin long ago observed that domesticated species often share physical changes — shorter noses, smaller teeth, floppy ears, altered pigmentation and other traits. A 2014 hypothesis known as "domestication syndrome" proposes a developmental mechanism linking these traits to selection for tameness and changes in neural crest cells during embryonic development.

Some experts urge caution about interpreting the new result as proof of domestication. Kathryn Grossman, a zooarchaeologist at North Carolina State University who was not involved in the work, said the shorter-snout phenotype could reflect other ecological or developmental pressures rather than the beginning of domestication. She also noted that historically domesticated species often have specific social structures — packs or herds with hierarchies — that raccoons do not clearly share.

Lesch acknowledges these complexities. She points out that pathways to domestication can vary — domestic cats and dogs have very different ancestral social systems yet both were domesticated — and argues that raccoons can exhibit social behaviors and tolerance of humans that might support human-associated adaptation.

Next steps

Lesch plans to validate the photographic results by measuring a historical collection of raccoon skulls at her university that span several decades. She also intends to compare behaviors of urban and rural raccoon populations to look for differences in tameness or human tolerance that would strengthen an interpretation of early domestication.

Without the ability to observe evolutionary change over millennia, researchers cannot yet say whether urban raccoons are on a trajectory toward full domestication or simply display an ecological adaptation with a similar appearance. If the process continued over many generations, Lesch notes, raccoons might eventually show additional traits associated with domestication — such as ear shape changes, altered fur patterns or curled tails — but for now the most valuable opportunity is to document the early stages of any such shift.

Sources: Raffaela Lesch (University of Arkansas at Little Rock); study published in Frontiers in Zoology; commentary from Kathryn Grossman (North Carolina State University).