When animals “kiss”: what nose-to-nose contact can tell us about behaviour and evolution
– by Sophie Lund Rasmussen
Kissing is often considered one of the most human of behaviours.
It feels intimate. Emotional. Social. And perhaps even a little mysterious. Why do we do it?
Interestingly, lip-to-lip kissing is actually very rare in the animal kingdom—only documented in humans, chimpanzees, and bonobos. But if we take a step back and look more broadly, many other mammals engage in a different kind of close-contact behaviour: nose-to-nose contact.
At first glance, it looks disarmingly similar. Two animals gently touching faces. It’s easy—perhaps inevitable—to interpret it as affection.
But as is often the case in behavioural biology, what we think we are seeing and what is actually happening may be very different.
A behaviour hiding in plain sight
Nose-to-nose contact is surprisingly widespread across mammals—from solitary hedgehogs to highly social bats, pigs, and even eusocial naked mole-rats. Yet, despite being so visually obvious, it has received remarkably little scientific attention.
That gap was the starting point for this study.
By taking a comparative approach—bringing together published observations and field insights across mammal species with very different social systems—I wanted to ask a simple question:
Does nose-to-nose contact serve the same suggested purposes across species—or is it something entirely different depending on context and levels of social organisation?
Information exchange
One of the clearest patterns that emerges is that the same physical behaviour can have very different functions depending on the species.
At its core, nose-to-nose contact is about information exchange.
Mammals rely heavily on chemical cues. Through close contact, individuals can assess each other’s identity, health, reproductive status, and even social rank.
But what animals do with that information varies dramatically.
The awkward encounter of hedgehogs
Take the European hedgehog.
If you imagine two hedgehogs touching noses, it is tempting to interpret it as something friendly—even affectionate. But the reality appears far less romantic.
Hedgehogs are solitary animals. They generally avoid one another and only interact under specific circumstances, such as mating or when feeding at feeding stations with cat food provided in residential gardens.
When nose-to-nose contact does occur, it seems almost accidental—arising during mutual sniffing rather than as an intentional social gesture.
And their reaction is striking.
After touching noses, hedgehogs often recoil, freeze, and appear momentarily “switched off,” as if overwhelmed by the sensory input. They may remain in this state for up to a minute, seemingly unaware of their surroundings.
From an evolutionary perspective, this is puzzling.
Why engage in a behaviour that temporarily leaves you vulnerable to predators?
One possibility is that the information gained is so valuable that it outweighs the risk. The contact may provide a rapid and concentrated burst of chemical signals—allowing individuals to quickly assess whether another hedgehog is a threat, a potential mate, or something to avoid.
Not exactly a romantic moment.
From information to social bonding
In more social species, however, nose-to-nose contact takes on a very different role.
In bats, for example, similar behaviours appear to function as greeting rituals and help reinforce social bonds when individuals reunite.
In pigs, nose-to-nose contact is part of a broader repertoire of “social nosing” behaviours. These interactions are associated with reduced aggression and even improved growth rates in piglets—suggesting a link between tactile social contact and physiological benefits.
Here, the behaviour is not just about gathering information—it is also about maintaining relationships.
In other words, something that may begin as a sensory mechanism could, over evolutionary time, become a social tool.
When contact becomes control
The story becomes even more intriguing in eusocial species like the naked mole-rat.
In these animals, nose-to-nose contact is part of a behaviour known as “shoving,” where dominant individuals—particularly the breeding female—physically push subordinates.
This behaviour plays a role in maintaining the colony’s social structure, including suppressing reproduction in non-breeding individuals.
What looks like a simple face-to-face interaction is, in this case, tied to power, hierarchy, and reproductive control.
It’s a striking example of how a behaviour can be repurposed—what evolutionary biologists call exaptation—from one function (information exchange) to something entirely different (dominance enforcement).
A continuum of meaning
Taken together, these examples suggest that nose-to-nose contact exists along a continuum depending on the level of social organisation:
- In solitary species: primarily incidental and sensory
- In social species: affiliative and communicative
- In eusocial species: regulatory and hierarchical
The behaviour itself remains broadly similar. But its meaning—and its evolutionary function—appears to shift depending on the social and ecological context.
Why this matters
At first glance, studying nose-to-nose contact might seem like a niche curiosity.
But it highlights something much broader.
Behaviour is not fixed. It is flexible, context-dependent, and shaped by both evolutionary history and current social environments.
The same physical action can mean entirely different things depending on who is doing it—and why.
