When a mouse finds its companion unconscious, it does not walk away or steal its food. It sniffs, grooms, and then—with its paws—pries open the companion's mouth and pulls out the tongue.
This is not an attack. It is first aid.
In February 2025, neuroscientist Wenjian Sun's team at the University of Southern California (USC) published a striking finding in *Science*: mice instinctively perform "first-aid behavior" on unconscious companions—ranging from gentle sniffing and grooming to vigorous tongue-pulling and airway clearing. In more than 50% of cases, this "first aid" revived the companion faster.
The discovery is groundbreaking not because "mice are smart," but because it forces us to rethink a fundamental question: how large a brain does altruism actually require?
An Accidental Discovery
The most dramatic part of the story: the researchers were not studying altruism at all.
Sun Wenjian first noticed the behavior accidentally during a completely unrelated experiment—a mouse repeatedly approached an anesthetized cage mate, sniffed it, licked it, and then began pulling at its tongue.
"I had never seen this behavior in mice before," Sun said.
The chance observation eventually became a *Science* paper.
A Structured Rescue Sequence
Researchers paired anesthetized mice ("patients") with awake mice ("helpers") and recorded everything with high-speed cameras. The helpers' behavior followed a structured progression:
1. Sniffing – assessing the patient's state, like a paramedic checking for breathing. 2. Grooming – licking the patient's body, especially the head, like checking vital signs. 3. Intense intervention – if the patient remained unresponsive, the helper escalated: biting open the mouth and pulling out the tongue, strikingly similar to the human "open the airway" maneuver.
Crucially, in control experiments, when researchers placed an inert plastic ball in the anesthetized mouse's mouth, helpers removed it in 80% of cases. But when the object was placed elsewhere (e.g., the anal or genital region), helpers ignored it entirely.
This shows the mice were not playing—they were specifically addressing an airway problem.
Helping Familiar Individuals Only
Helpers rescued familiar cage mates almost immediately, with greater intensity and duration. Toward unfamiliar mice, they approached and sniffed but rescue behavior was markedly reduced. And toward mice that were simply sleeping or active, they showed almost no special behavior—mirroring how humans distinguish someone who needs help from someone who is merely napping.
The Brain: A Dual Oxytocin Pathway
The USC team used optogenetics and calcium imaging to show that the medial amygdala, a key region for social behavior, is strongly activated during rescue.
A follow-up study published in *PNAS* in April 2025 by Hui Li's team (Institute of Psychology, Chinese Academy of Sciences) and Zhoufeng Chen's team (Shenzhen Medical Academy of Research and Translation) revealed oxytocin acts through two parallel pathways:
- Central amygdala pathway — "feeling distress." When the helper detects the companion's distress signals, oxytocin neurons in the hypothalamic paraventricular nucleus release oxytocin into the central amygdala, decoding the emotional meaning: "something is wrong with my companion."
- Dorsal bed nucleus of the stria terminalis pathway — "taking action." Simultaneously, oxytocin is released in the dorsal BNST, driving the concrete rescue actions: licking, grooming, tongue-pulling.
Helping Others Relieves One's Own Distress
During rescue, helpers' stress hormone (corticosterone) levels rose—but once the companion revived, the helpers' stress levels fell.
Helping others also relieves one's own suffering. This is not pure self-sacrificial altruism but a subtle, sustainable reciprocal mechanism: see a companion in distress, feel uneasy, act, recover together. In natural selection, individuals wired this way would survive better in groups.
The seed of altruism may not be planted in morality, but in anxiety.
An Evolutionary Lineage from Dolphins to Mice
Dolphins lift sick companions to the surface to breathe; elephants support injured ones with their trunks; chimpanzees lick each other's wounds. But mice—with brains the size of a peanut—suggest this behavior's evolutionary roots run far deeper, possibly back to the common ancestor of all mammals.
Altruism may not be a product of "higher intelligence" but a basic mammalian configuration—written into our deepest biological code, like heartbeat and breathing.
Should We Anthropomorphize?
The researchers caution against over-anthropomorphizing: mice's rescue behavior may be instinctive rather than a conscious decision. But the same neurochemical events—the oxytocin system, amygdala responses, corticosterone fluctuations—we call "empathy," "anxiety," and "relief" in humans. Same molecules, same brain regions, same response patterns. Different in degree, homologous in mechanism.
Perhaps the truth is not "mice are like humans," but "humans are mammals too." Our altruism is not a miracle of civilization appearing from nowhere, but an instinct inherited from mammalian ancestors over 100 million years ago—merely dressed up more elaborately by language, culture, and moral philosophy.
Epilogue
A mouse weighing less than 30 grams, prying open its companion's mouth and pulling out its tongue, knows nothing of CPR, airway obstruction, or the golden four minutes. It only knows: my companion has gone still, that makes me uneasy, and I must do something.
That impulse to "do something" may be the starting point of all altruistic behavior—from a mouse pulling a tongue, to a human dialing emergency services, to international rescue teams rushing to disaster zones. The scale differs, but the underlying code may be the same.
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References: 1. Sun, W. et al. "Reviving-like prosocial behavior in response to unconscious or dead conspecifics in rodents." *Science* (2025). DOI: 10.1126/science.adq2677 2. Zhang, F.-R. et al. "Distinct oxytocin signaling pathways synergistically mediate rescue-like behavior in mice." *PNAS* (2025). DOI: 10.1073/pnas.2423374122