We are learning more and more every day about just how smart some animals are: apes, octopuses, some species of birds, dogs, cats. But how about other animals? Snails? Mosquitos? They sure seem less smart. Still smarter than plants though. Because it would be difficult to argue that plants are intelligent. Or would it?
In a new study, it was shown that plants emit sounds when they are distressed. And these sounds are very different depending on whether they have recently been cut or whether they don’t have enough water. The sounds are not audible to the human ear, as they are between 20 and 100 kilohertz, which is above the threshold of human hearing (which usually has the upper limit of 15-17 kilohertz).
These are fascinating results. But we should be careful with what the study shows and what it doesn’t. It is tempting to frame these results as «crying» and that is exactly what the popular science press has been doing. Plants don’t suffer in silence: they are screaming with pain.
This is a beautiful illustration of how easily we slip into anthropomorphizing not just animals, but also plants. Anthropomorphism is the attitude of attributing human-like features and mental states to animals (and plants). It has been widely discredited in biology as an unproductive method for finding out more about animal cognition (and also about how plants function). (A much more promising method would be the exact opposite of anthropomorphism, what could be called zoomorphism, when we attribute features and mental states that we know from the study of animals to humans.)
Anthropomorphism makes it easier to relate to findings like the one about plants emitting sound — crying in distress is something that resonates with us more than the scientific language of air bubbles in the xylem of plants, which is the actual mechanism of the sound production in plants. But as of now, there is no reason to think that the sounds plants produce would count as communication in any meaningful sense of the term.
There is no evidence that they are heard by anyone (although theoretically some animals — bats, moths, mice — could actually hear it as their ears are sensitive to the frequencies of the plant sounds). And it could very well be a byproduct of the physical condition of these plants: less water in the system leads to more air bubbles in the xylem (in the little tubes that transport water in plants), which leads to the sound of the popping of these bubbles.
Is this a disappointing explanation? I don’t think so. The aim is to understand why plants do what they do. And the results about the emitted sounds contribute to this body of knowledge. They could even lead to better ways of controlling the needs of plants in horticulture by audio monitoring. All of this is true even if the plants don’t strictly speaking «cry» or «scream».
Plus, no guilt next time you mow your lawn…