flashing lights, chirping calls, croaking songs and elaborate dances. But new research from Northwestern University suggests many of these signals share a surprising feature: They repeat at nearly the same tempo.
In a new study, Northwestern scientists found that communication signals across a wide range of species tend to repeat at about 2 hertz, or roughly two beats per second.
The researchers propose this tempo might reflect a shared biological constraint. Animal brains, including humans, may be naturally tuned to process signals arriving at that pace. In other words, two beats per second may be a rhythmic "sweet spot" that enables brains to detect signals more easily and process communication more efficiently.
Understanding this potentially universal tempo could help scientists better interpret animal signaling and social behavior across species. The findings also hint that human perception of rhythms, including beats in popular music and the cadence of speech, may arise from the same neural timing principles found throughout nature.
The study was published today (April 14) on in the journal PLOS Biology.
"There seems to be an abundance of organisms signaling or communicating at a relatively narrow band of tempos," said Northwestern's Guy Amichay, who led the study. "They all seem to stay around 2 or maybe 3 hertz. In principle, they could communicate at other rhythms. Physically, there is nothing preventing them from communicating at, say, 10 hertz, yet they do not. To explain this phenomenon, we propose that this tempo of 2 hertz might be easier to understand because it resonates with your brain. It resonates with the human brain, firefly brain, sea lion brain, frog brain and so on."
"There's a somewhat subtle point here: we suspect that getting the 'carrier' signal in the right tempo range is key to communicating efficiently," said Northwestern's Daniel M. Abrams, the study's senior author. "It might not be that the tempo itself conveys any information, but it just serves as a baseline for getting attention, with actual content sent on top of it like musical notes following along with the beat in a song."
Amichay is a research associate in Abrams' laboratory at Northwestern. An expert on synchronization and pattern formation, Abrams is a professor of engineering sciences and applied mathematics at Northwestern's McCormick School of Engineering and co-director of the Northwestern Institute on Complex Systems (NICO), as well as a member of the National Institute for Theory and Mathematics in Biology (NITMB). Amichay and Abrams co-authored the study with Vijay Balasubramanian, the Cathy and Marc Lasry Professor of Physics at the University of Pennsylvania.
Interactions between light and sound
The study grew out of Amichay's project to understand how synchrony arises in nature. Along with some lab mates, Amichay visited Thailand to collect footage of firefly swarms, blinking together in the countryside. As he gazed at the fireflies for hours, Amichay could not help but notice an uncanny coincidence.
"At some point, I thought that the flashing of the fireflies and the chirping of the nearby crickets were in sync with each other," Amichay said. "My colleagues noticed it too, and we thought that it was crazy that these two unrelated species would interact in such a way."
After analyzing their own recordings, the team concluded that the species were not synchronizing with one another. Instead, they were sending independent signals at very similar tempos - around two-to-three pulses per second.
To investigate whether the firefly-cricket coincidence reflected a broader pattern, Amichay and Abrams analyzed previously published studies of animal communication across a wide range of species. These rhythmic signals included: firefly flashes, cricket chirps, frog calls, birds' mating displays, sound and light pulses from fish and vocals and gestures from mammals.
Despite enormous differences in body sizes, habitats and communication methods, the team found that many species repeat signals within a narrow range of roughly 0.5 to 4 hertz (1 to 4 beats per second). The pattern spans animals that communicate through sound, light or movement, suggesting a common underlying principle.
"If you try to catch a firefly, it panics and flickers much faster," Amichay said. "Biomechanically, they are able to signal faster. So, we wondered if there might be a deeper reason why very different systems signal at this tempo and not any other tempo."
From crickets to concerts
As Amichay and Abrams searched for a hidden principle, they happened to meet Balasubramanian, who studies neuroscience and theoretical physics, at an NITMB conference. Balasubramanian noted that the biophysics of a single neuron operates at the same rhythm. Neurons require time to integrate information before firing again. Because of this biological constraint, neural circuits tend to respond most strongly to signals arriving every few hundred milliseconds - roughly two times per second.
To test this idea, the team built computer models of simple neural circuits and examined how they responded to signals at different tempos. According to the models, the circuits respond most strongly to signals within the same 2 hertz range observed across animal communication. That means communication signals may have evolved to match the rhythms that brains process most easily.
According to Amichay, musicologists have long noted that popular songs cluster around 120 beats per minute, which is exactly 2 hertz.
"That rhythm fits our body; it fits our limbs," he said. "We walk roughly at 2 hertz, so it's easy for us to dance to music that's 2 hertz. Of course, more experimental music can have drastically different beats. But if you turn on the radio and hear Taylor Swift - that's often 2 hertz."
Amichay said he hopes the study inspires other researchers to examine a broader range of species and directly measure how brains respond to different communication rhythms. Those efforts could reveal whether this potentially universal tempo is a fundamental feature of neural systems and possibly lead to new insights into how it influences behavior across species.
"It's tempting to think there's a deeper connection here - that maybe we're all on the same shared wavelength," Amichay said. "But we're still exploring what this might mean."
The study, "A universal animal communication tempo resonates with the receiver's brain," was supported by NICO, the Buffett Institute for Global Affairs and the National Institute for Theory and Mathematics in Biology.
