Journal: Biosemiotics Pattern without Message: From Environmental Organization to Selective Relevance
This study demonstrates that living systems like *Saccharomyces cerevisiae* respond to specific, persistent acoustic patterns in their environment rather than the source signal itself, illustrating a "double selection" process where the medium filters available differences and the organism selectively engages with them to enable semiotic scaffolding without constituting full semiosis.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Living things are constantly bombarded by the physical world. A breeze brushes against a leaf, a shadow falls across a pond, and a sound wave ripples through the air. Yet, for an organism to survive, it cannot treat every single physical difference as important. If a cell reacted to every tiny fluctuation in its surroundings, it would be overwhelmed. The central puzzle of how life works is understanding how a living thing decides which of these endless physical differences actually matter. Some differences are just noise, while others trigger a change in behavior, growth, or development. This process of filtering the world down to what is biologically significant is the starting point for understanding how life interacts with its environment.
Scientists have long known that an organism does not experience the world exactly as it is in physics. Instead, it lives in a personal world shaped by its own needs and senses. A sound that is just a vibration to a rock might be a warning signal to a bird. But before a sound can become a signal, it must first survive the journey from its source to the organism. When a sound travels through water, air, or the walls of a container, it changes. It gets distorted, some parts get louder, and others get quieter. The question this research team set out to answer was simple but profound: what does the sound actually look like when it finally arrives at the living cell, and does that specific shape of the sound matter to the cell?
To find the answer, the researchers turned to a very simple form of life: baker's yeast. Yeast is a single-celled fungus that has no ears, no brain, and no nervous system. It cannot hear in the way humans or animals do. This made it the perfect subject for the experiment because any reaction it showed could not be explained by "hearing" a message or recognizing a voice. The scientists wanted to see if the physical structure of the sound itself, stripped of any meaning, could still influence the cell. They exposed yeast cultures to five different types of sound: synthetic tones, human singing, whistling sounds, short impulse noises, and broad, static-like noise.
However, the researchers knew that the sound generated by their speakers was not the same sound the yeast actually experienced. The sound had to travel through a rubber interface, a glass test tube, and the liquid medium holding the yeast. As it moved through this system, the sound waves bounced, interfered with each other, and changed. To understand what the yeast was truly feeling, the team placed a sensitive underwater microphone, called a hydrophone, exactly where the yeast cells were sitting. They recorded the sound as it existed inside the liquid, not as it was sent out by the machine.
What they discovered was that the environment acted like a filter that reshaped the sound in complex ways. The sound that arrived at the yeast was not just a quieter version of the original; it was a new acoustic condition with its own unique structure. Some regular patterns in the sound were preserved, while others vanished completely. For instance, the rhythmic regularity of a singing voice or a synthetic tone was often scrambled as it passed through the glass and liquid, losing much of its original timing. However, other features, such as the stability of the sound's energy over time, remained surprisingly intact. The researchers created a way to measure these surviving features, combining them into a single score that described how "structured" the sound was once it reached the cell.
When they compared this score to how the yeast reacted, a clear pattern emerged. The yeast did not respond to the loudness of the sound, nor did it react to the specific type of sound source, such as whether it was a human voice or a machine tone. Instead, the yeast responded to the amount of organization that remained in the sound after it passed through the environment. When the sound arriving at the cells had a high degree of this remaining structure, the yeast showed a significant change in its growth rate. In contrast, when the sound that arrived was disorganized and chaotic, the yeast showed almost no reaction.
The team looked deeper than just growth rates. They examined the internal architecture of the yeast cells, specifically the network of protein fibers that give the cell its shape and help it move. Under the microscope, they saw that cells exposed to highly structured sounds organized their internal fibers in a clear, polarized way, preparing themselves for a specific direction of growth. Cells exposed to disorganized sounds, however, kept their fibers scattered and diffuse. This difference in internal structure was also visible in how the cells changed shape when stimulated to reproduce. The cells exposed to structured sounds formed distinct, elongated projections, while those exposed to unstructured sounds remained round and unformed.
The findings suggest a two-step process of selection. First, the physical environment selects which parts of the sound survive the journey. The glass tube and liquid medium act as a gatekeeper, deciding which patterns remain available. Second, the organism selects which of those surviving patterns are relevant. The yeast did not react to every sound that reached it; it only responded to the ones that maintained a certain level of structural order. This means that the environment itself plays an active role in shaping what a living thing can perceive, long before the living thing makes any decision about what to do.
This study does not claim that yeast is "listening" or that the sound is a message with meaning. The yeast is not interpreting the sound as a song or a warning. Instead, the research highlights a fundamental step that happens before meaning exists. For a difference in the world to become a signal, it must first persist as a stable, organized pattern through the physical medium. The environment provides the raw material of organized differences, and the living system then engages with those specific patterns. The sound that matters to the yeast is not the one that was played, but the one that actually arrived, reshaped by the world it traveled through. This work offers a new way to look at how life connects with its surroundings, showing that the physical structure of the environment is just as important as the biological machinery of the organism in determining what gets noticed.
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