One evening in Thailand, while researchers were filming firefly swarms Pteroptyx malaccaesomething small and decisive happened. The flashes of insects and the chirping of nearby crickets seemed to go in almost the same pace. Subsequent analysis showed that there was no real synchrony between the two species, but their cadence remained surprisingly close: around 2.4 pulses per second, with a difference of around 10%. That coincidence sparked a broader investigation, published on PLOS Biologywhich leads to a fascinating conclusion: in the animal world, communication often tends to concentrate around 2 hertz.
We’re not just talking about sounds. This range includes signals produced by voice, light and movement. The vocalizations of mammals, the singing of birds, the calls of frogs, the flashes of fireflies, even some rhythmic performances observed in very different species. The common trait is not the means used to communicate, but the time with which the signal returns. And that time, very often, falls between 0.5 and 4 hertz, that is, between one and four beats per second.
From the flashes of fireflies to the calls of birds, frogs and mammals
To understand whether that Thai observation was just a curiosity, the Northwestern University group reviewed previously published studies on a wide variety of species. Insects, crustaceans, amphibians, birds, fish and mammals, including primates, humans and sea lions, come into the picture. The authors write that this pattern appears across eight orders of magnitude of body weight, so in very small animals and in others enormously larger, without the rhythm really dispersing.
To reduce the risk of constructing the result by choosing only the most convenient examples, the researchers also combined the literature with a random check. They took 50 isochronous signals from the xeno-song bioacoustic database, ten for each of five animal groups: birds, bats, frogs, grasshoppers and land mammals. There too the distribution returned to the same area. It is one of the most interesting passages of the work, because it gives a little more weight to the idea that it is not just a suggestive impression.
The data is even more striking for a simple reason: many of these animals, on a physical level, could communicate even faster. The authors write it clearly. A frightened firefly, for example, accelerates its flashes. The limit, therefore, does not seem to lie only in biomechanics. The feeling is that there is a kind of favorable zone, a point where the signal reaches those who need to receive it with maximum effectiveness.
The brain could be the profound reason for this cadence
Here the strongest part of the hypothesis comes into play. According to the authors, that band between 0.5 and 4 hertz coincides with the delta band, i.e. the slowest brain rhythm commonly identified in neuroscience. The idea is that brains, in very different species, are predisposed to better process signals that arrive at that pace, because neurons need a few hundred milliseconds to integrate the information before firing again.
To test this possibility, the team built computer models of small neural circuits. The result goes in the same direction as the data observed in animals: these circuits respond with greater intensity precisely to the signals that fall within the range seen in the study. In essence, the researchers propose that many communication systems have evolved by adapting to rhythms that brains can process with less effort and more efficiency.
It’s impossible not to think about the connection with music. In the note released by Northwestern, Guy Amichay recalls that musicologists have long observed how many popular songs are around 120 beats per minute, which is exactly equivalent to 2 hertz. It is a cadence that also seems to adhere well to the human body, to the pace of walking, to the ease with which one follows a rhythm and moves along it. Another notable detail also appears in the paper: recent work has shown that the intonation units of human language fall within the same time window.
This does not mean that all living things always and only communicate at that frequency. The authors themselves urge caution: the work is exploratory, built on a non-exhaustive collection of already existing studies, so the risk of selection bias remains. It will require broader observations, other species, and direct tests of how brains respond to different signals. Meanwhile, that rhythm resurfaces often enough to leave a clear idea: when life needs to make itself understood, it often ends up beating there.
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