The Universal Language of Rhythms
Humans are creatures of rhythms. From the earliest days of our existence, we have sung and danced, creating and recognizing patterns that resonate through time. We can identify a song by its rhythm alone, regardless of whether it is played fast or slow. This ability to detect rhythmic patterns seems almost effortless, and for a long time, we believed this skill required the large and complex human brain.
However, new research published in the journal Science challenges this assumption. Our study shows that humans are not the only species capable of mastering rhythm. Even the bumblebee, with a brain the size of a sesame seed, has demonstrated an impressive ability to learn abstract rhythms.
Rhythms in Nature
Rhythms are everywhere in nature. We hear them in the songs of birds and frogs, the ultrasonic hunting chirps of bats, and even in the flashing displays of fireflies. We see them in the rhythmic shakes of a peacock’s tail, the waggle dances of honey bees, and the courtship dances of fruit flies.
For a long time, we assumed these were innate behaviors—animals were simply following evolved programs rather than learning rhythms. While humans and a few other species, such as certain birds and mammals, have shown the ability to recognize rhythmic structures regardless of speed, this was thought to require a large brain.
But most animals in the animal kingdom have tiny brains compared to humans, yet they manage to solve the problems necessary for survival. The question remains: can they recognize rhythm?
Training Bumblebees to Recognize Rhythms
To explore this, our team from Southern Medical University and Macquarie University worked with bumblebees. These big, beautiful bees are easy to keep and train, and they are highly motivated to collect nectar to take back to their nests.
We trained individual bumblebees to forage from artificial flowers equipped with LED lights that we could control. One pattern of flashing lights offered a sugary treat, while another did not. The only way the bees could distinguish between the patterns was by their rhythmic structure. In this way, we taught the bees to prefer one rhythmic pattern over another, such as dot-dash-dot-dash versus dot-dot-dash-dash.
After training the bees for an afternoon, we tested them on flashing flowers that offered no sugar. We found that the bees preferred to visit the flower that had been associated with a reward during training. This showed that they could learn to recognize a rhythm linked to a reward.
Even more impressively, the bees could recognize their trained rhythm regardless of whether it was played faster or slower. This indicates that they had learned a flexible rhythm, which is the first evidence of such an ability in bees.
Recognizing Rhythms in Different Forms
To further test the bees, we asked whether they could recognize a rhythm regardless of how it was presented. Bees are deaf at the frequencies we can hear, but they are very sensitive to vibrations. We trained bumblebees in a maze with a vibrating floor at the junction.
We made the floor pulse with rhythm, teaching the bees that one rhythm (dot-dot-dash-dash) meant the sugar reward was in the left arm of the maze, while another rhythm (dot-dash-dot-dash) meant the reward was in the right arm.
We knew the bees could learn the maze because their success in finding the sugar improved with training. Once the bees were well-trained, we changed the maze so that there was a flashing LED light at the junction instead of a vibrating floor.
The bees trained with vibration were able to use the rhythmic pulses of light to determine which arm of the maze to choose. This demonstrated that the bees could recognize a rhythm regardless of how it was presented. In other words, the bees had a sense of abstract rhythm.
As far as we know, this ability has only been observed in humans before.
Changing Our Understanding of Rhythm
The success of bumblebees in these rhythm-learning tests changes how we think about what is needed to perceive and learn rhythm. In humans and mammals, rhythm learning involves multiple regions of the brain, making it a complex process.
However, perhaps there are simpler ways for a tiny brain to achieve similar results. Brains themselves are full of rhythms, as neurons pulse with impulses. Many neural circuits use rhythmic properties of synchronous and asynchronous nerve impulses to organize their function. It’s possible that something in the rhythmic properties of brains allows them to detect rhythms in nature.
If we can understand this mechanism, we could develop lightweight solutions for speech and music recognition, diagnose heart irregularities, or detect pre-epileptic brain waves.
Andrew Barron receives funding from the Australian Research Council, Templeton World Charity Foundation, Horticulture Innovation and the Ian and Shirley Norman Foundation. He is a member of the Agrifutures Australia Honey Bee and Pollination Advisory Panel.
