Natural selection is an indifferent mother. Crying babies trigger sympathetic nervous reactions in our species — but make primordial reptiles with huge, sharp teeth salivate.
Terrifyingly, at least one predator can sense a baby’s distress more acutely than we can. That’s the grim state of nature according to “Crocodile perception of distress in hominid baby cries,” recently published in the journal of The Royal Society.
Looking for a predation trigger
I know what you’re thinking: who signed off on this testing protocol?
But as the team described in the abstract, its experiments were less than grisly. The study sourced recordings of human, bonobo, and chimpanzee infants crying, then played them for Nile crocodiles and watched what happened.
The researchers aimed to do two things. One, establish confidence that the crocs could translate a given hominid nugget’s vocal distress into a predation trigger, and two, identify the specific acoustic mechanisms they used in the process.
Results were encouraging, as the Smithsonian reported. (Or discouraging, depending on your species and maternal/paternal status.)
Nile crocodiles get hungry and go into search-and-destroy mode when they hear an infant meltdown. Because of the auditory cues they rely on during a hunt, they probably sense children’s cries for help better than we do.
The researchers found the crocodiles responded most strongly to deterministic chaos, harmonicity, and spectral prominences on the tapes. If you can’t rattle off definitions for these terms off the top of your head, don’t be too hard on yourself — in this context, we’re not wired to respond to them, anyway.
An innate response
The study authors called the criteria we use to decode infant stress signals “different,” but the writing is on the wall — we’re just not as good as the crocodiles.
“Interestingly, the acoustic features driving crocodile reaction are likely to be more reliable markers of distress than those used by humans,” the paper says.
So if your young child throws a temper tantrum with a Nile crocodile within earshot, should you arm yourself and get ready for a deathmatch (or, failing that, just get out of the way and try not to look)? On the surface, the study looks about as cold-blooded as it gets. But it may also hold some kernel of beneficence. Some female crocodiles might react to the noises in response to their own maternal instinct.
“They just react, more because it triggered some probably innate response,” Élodie F. Briefer, a behavioral ecologist at the University of Copenhagen who was not involved in the research, told The Smithsonian. “That might be a predatory response, to prey in distress, or it could be because the sound resembles a bit what their own offspring are doing.”
Just another day in the circle of life.
