For humans, there’s no way to instantly recognize family members we’ve never seen before. Sure, we can pick up on clues, like similar appearance or a shared last name, but there’s nothing deep down that tells us: “That’s your relative.”

But the opposite is true for mice. They know a family member when they see one—or rather, when they smell one. That's what new research in the journal Current Biology suggests.

Scientists have long struggled to understand how mice can instantly recognize relatives they’ve never met. Female mice, in particular, are known to identify female relatives, and enlist them as nest partners while they raise their young.

For years, scientists believed mice, and other vertebrate animals, recognized kin through a genetic marker called the major histocompatibility complex (MHC). The marker is vertebrate-wide, which means that, were the marker responsible for kin recognition, it would affect a range of animals. 

But now, scientists from the University of Liverpool have found that mice use a different genetic marker, called the major urinary protein (MUP), to identify each other. The protein, which is detected through scent, is species-specific; only mice have it. 

The MUP allows mice to avoid in-breeding and cooperatively raise their young—a strategy which increases overall breeding success for individual mouse families. 

Though the study’s findings are fascinating on their own, they also have broader implications for future studies. Study co-author Jane Hurst explained to Science Daily, “This work extends far beyond any previous attempt to identify the genetic basis of kin recognition in vertebrates and strongly challenges the current assumption that there is a common kin-recognition mechanism ‘inbuilt’ into the immune physiology of all vertebrates.”

The mouse study raises a big question for all species: To what degree do other animals recognize kin through genetic markers? While it’s now clear that all vertebrate animals do not share the same genetic marker, that doesn’t mean some other species don’t have their own. 

[h/t: Science Daily]