I Have No Mouth, Yet Still I Scream

In light of the recent open letter from AI leaders for a moratorium on AI development, I’m declaring a temporary moratorium on writing about it too, although I doubt either one will last long (and this week’s title is, if you hadn’t noticed, an homage to Harlan Ellison’s classic dystopian AI short story).  Instead, this week I want to write about plants. Specifically, the new research that suggests that plants can, in their own way, scream.

Bear with me.

Credit: Robert Krulwich/NPR

To be fair, the researchers don’t use the word “scream;” they talk about “ultrasonic airborne sounds,” but just about every account of the research I saw used the more provocative term.  It has long been known that plants are far from passive, responding to stimuli in their environment with changes in color, smell, and shape, but these researchers “show that stressed plants emit airborne sounds that can be recorded from a distance and classified.”  Moreover, they posit: “These informative sounds may also be detectable by other organisms.”  

It should make you wonder what your houseplant is saying about you when you forget to water it or get a cat. 

They basically tortured – what else would you call it? – plants with a variety of stresses, then used machine learning (damn – I guess I am writing about AI after all) to classify, with up to 70% accuracy, different categories of responses, such as too much water versus too little.  Even plants that have been cut, and thus are dying, can still produce the sounds, at least for short periods.  They speculate that other plants, as well as insects, may be able to “hear” and respond to the sounds.

The ultrasonic sounds are believed to be produced through a process known as cavitation, which is a well-known process during which pressure variations in a liquid create small bubbles that collapse and generate shock waves.  The specific mechanism for this hasn’t been identified.

Here is what it sounds like:

The research mainly used tomato and tobacco plants, but also found that other plants, including corn, wheat, grape, and cactus, also emitted the sounds.  “We can separate between sounds emitted by tomato and tobacco, between tomato and cacti, and also between cut tomato and dry tomato a little bit dry tomato and very dry tomato,” lead researcher Lilach Hadany, a professor at Tel Aviv University, told Business Insider.

“When these plants are in good shape, they produce less than one sound per hour, but when stressed they emit many more, sometimes 30 to 50 per hour,” said Professor Hadany.  Her team had previously shown that plants can “hear,” such as when bees buzzing nearby cause them to produce more nectar.

“These findings can alter the way we think about the plant kingdom, which has been considered to be almost silent until now," the authors write.  “Our results, demonstrating the ability to distinguish between drought-stressed and control plants based on plant airborne sounds, open an avenue of research in the field of precision agriculture.”

Instead of blithely fertilizing and watering them, on our schedules, plants may be telling us exactly what they need, when.

It gets even more interesting. "Even in a quiet field, there are actually sounds that we don't hear, and those sounds carry information. There are animals that can hear these sounds, so there is the possibility that a lot of acoustic interaction is occurring," explains Professor Hadany.  “So now that we know that plants do emit sounds, the next question is—‘who might be listening?’ We are currently investigating the responses of other organisms, both animals and plants, to these sounds, and we’re also exploring our ability to identify and interpret the sounds in completely natural environments.”

Credit: Khait, et. alia.

Not everyone is convinced that communication is happening.  “Lots of sounds in the world are generated that are not ‘intentional’ signals, but nonetheless can be heard and used by other organisms for their own benefits. So, the concept of communication is indeed a challenge … does it need to be bi-directional to work and be considered as such?” Daniel Robert, a professor of bionanoscience at the University of Bristol’s School of Biological Sciences, told CNN.  He was not involved in the research.

As to whether the sounds suggest that plants have “feelings” as we might think of them, “I think we are not there yet," Professor Hadany admits. "We cannot say the plant feels stress and therefore makes sounds. It might be that the sounds are made completely passively, like a physical process.”

---------------

This all reminds me over the furor a few years ago about the “Wood Wide Web,” a hypothesis that trees communicated through their roots via a network of fungi, although this remains controversial.  The point, though, is that there is a lot more communication going on in nature than we realize. We used to think we were the only animal that communicated, the only social animal, the only tool-using animal, and all those have been debunked. Now, if plants can scream, the lines between animal and plant are getting less well-defined.

Similarly, the line between “us” and our microbiome is getting very fuzzy. It’s long been known that not only do our microbiome cells outnumber “our” cells but also their DNA vastly outnumbers ours.  Who is really “us”? 

Moreover, our microbiome is actively communicating with us, not only in the gut (where the largest numbers are) but also with the brain and other organs.  That communication at least influences our health, such as with MS or depression.  It turns out that cancer cells have their own microbiome (and mycobiome).  More connections will be discovered, such as the effect on inflammation, which may underlay heart disease and autoimmune disorders.

Unfortunately, we know more about what plants are communicating with the world than what our microbiome is communicating with us. 

It all reinforces my belief that the 21^st century is going to be the century of biology – whether it is computing, industry, or medicine. Yet we’re still dousing everything in antibiotics and wrecking havoc on our microbiome, with unknown (but probably terrible) consequences. 

So perhaps we should be doing a better job of listening to plants, and figuring out what else in nature we should be paying better attention to. Our health may depend on it.