In the complex social world of mice, a newcomer can instantly size up a stranger’s social rank without ever having met them before. A new study from the Francis Crick Institute shows these rodents rely on their keen sense of smell to make quick social judgments – using chemical cues to decide whether to stand their ground or back down during confrontations.
The research, published this month in Current Biology, overturns previous assumptions about how hierarchies form among animals, revealing a sophisticated system of chemical communication that helps mice navigate social situations efficiently.
Chemical Messages Reveal Social Standing
When strange mice meet in a narrow tube, they don’t need past experience to know which should retreat. Instead, they use their extraordinary sense of smell to detect invisible status signals.
“We’ve shown that mice weigh up strangers using chemical cues and can detect social status without needing an extensive history of confrontations with those specific opponents,” explains Neven Borak, former PhD student at the Crick Institute and the study’s first author.
How exactly do mice recognize who’s boss? Researchers discovered mice rely on two separate chemosensory systems – both their standard sense of smell (the olfactory system) and a specialized system for detecting chemical signals through physical contact (the vomeronasal system).
What’s remarkable is that either system alone is sufficient – only when researchers experimentally blocked both systems did the mice lose their ability to recognize social rank.
Beyond Fixed Behaviors
The study challenges previous theories about social hierarchies in animals. Rather than displaying fixed behaviors regardless of opponent (such as being naturally aggressive or submissive), mice adjust their behavior based on their perception of their opponent’s status relative to their own.
When researchers tracked behaviors during confrontations, they found:
- Mice pushed more when facing lower-ranked opponents
- They retreated more often when facing higher-ranked opponents
- These behaviors weren’t fixed traits but changed depending on who they faced
- Body size and physical attributes didn’t determine outcomes
Conflicts resolved faster between familiar mice than strangers, suggesting that while chemical signals provide essential rank information, social recognition accelerates conflict resolution.
Universal Rank Signals
Could these findings help explain human social behavior too? While we don’t primarily use scent to determine status, humans similarly make quick judgments about others’ social standing based on visual and verbal cues.
“This is a fascinating phenomenon that humans do too, mostly using visual cues,” notes Borak. “Our work offers an interesting perspective on social mobility: humans, like mice, can enter a new group of people but still maintain understanding of own social rank and gauge the social status of unfamiliar people.”
The study also revealed that mice can track changes in social status. When researchers artificially elevated a mouse’s rank by painting it with urine from a dominant male, other mice – even unfamiliar ones – treated it according to its new, higher status.
Brain Decision-Making
What happens in the brain when a mouse evaluates social rank? Jonny Kohl, Group Leader at the Crick and senior author, explains: “We’ve shown for the first time how mice integrate internal and external information about dominance. This shows that a decision based on relative ranks is made in the brain before mice show either aggression or submissive behaviour, rather than there being fixed differences in behaviours leading to an aggressive or docile mouse.”
The team now plans to investigate which brain regions process information about both the opponent’s rank and the mouse’s own rank before initiating a decision to retreat or advance.
Beyond Mouse Society
What makes these findings particularly intriguing is how they might inform our understanding of social hierarchies across species. Many animals, including humans, live in social structures where understanding relative status helps minimize conflict and establish social order.
Despite our reliance on different sensory systems, the underlying mechanisms of social rank recognition may be more evolutionarily conserved than previously recognized.
Could future research reveal similar neurological pathways in humans that help us navigate complex social hierarchies? As scientists continue to unravel the biological basis of social behavior, we might discover even more similarities in how various species – from mice to humans – process social status information.
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