An advocate of plant intelligence, the Italian author discusses the complex ways in which plants communicate, whether they are conscious, and what his findings mean for vegans
Born in Calabria in 1965, Stefano Mancuso is a pioneer in the plant neurobiology movement, which seeks to understand “how plants perceive their circumstances and respond to environmental input in an integrated fashion”. Michael Pollan in the New Yorker described him as “the poet-philosopher of the movement, determined to win for plants the recognition they deserve”. Mancuso teaches at the University of Florence, his alma mater, where he runs the International Laboratory of Plant Neurobiology. He has written five bestselling books on plants.
What’s at the root of your love of plants?
I began to be interested in plants at university. One of my tasks during my doctorate was to understand how a root growing in the soil was able to move around an obstacle. My idea was to film this movement, but I saw something different: the root was changing direction well before touching the obstacle. It was able to sense the obstacle and to find a more convenient direction. That was my first eureka moment, where I started to imagine that plants were intelligent organisms.
You refer to your field as plant neurobiology. Is this a provocation?
At the beginning, it was not at all. I started to think that almost all the claims I was hearing about the brain were valid also in plants. The neuron is not a miracle cell, it’s a normal cell that is able to produce an electrical signal. In plants, almost every cell is able to do that. The main difference between animals and plants, in my opinion, is that animals concentrate specific functions inside organs. In the case of plants, they diffuse everything through the whole body, including intelligence. So it was not a provocation at the beginning, but there was a big resistance among my colleagues to use this kind of terminology, and so after it became a provocation.
What were you hoping to achieve with your new book, Tree Stories?
What I’d like to popularise is, first, the many abilities of plants that we normally are unable to feel and understand, because they are so different from us. Second, when you tell a story about life on this planet, not talking about plants, which make up 87% of life, is a nonsense.
You argue passionately in favour of filling cities with trees. Why is this so important?
We are producing 75% of our CO₂ in cities, and the best way to remove that CO₂ is by using trees. The closer the tree is to the source of carbon emissions, the better they are at absorbing it. According to our studies, we could put around 200bn trees in our urban areas. To do that, we really need to imagine a new kind of city, completely covered by plants, without any border between nature and city.
You have a fascinating chapter about a tree stump being kept alive for decades by its neighbouring trees. What can humans learn from tree communities?
Plants are so incredibly cooperative with one another because cooperation is the most efficient way to grant the survival of species. Not understanding the strength of the community is one of [humanity’s] main errors. There was a very clever evolutionary biologist at the beginning of the last century, Peter Kropotkin, who said that when there are fewer resources, and the environment is changing, then cooperation is vastly more efficient [than competition]. This is an important teaching for us today, because we are entering a period of reduction of resources and the environment is changing because of global warming.
To what degree can plants communicate with one another? If you have a spectrum with rocks at one end and humans at the other, where do plants sit?
I would say very close to humans. Communication means you are able to emit a message and there is something able to receive it, and in this sense plants are great communicators. If you are unable to move, if you are rooted, it’s of paramount importance for you to communicate a lot. We experienced this during lockdown, when we were stuck at home and there was an incredible increase in traffic on the internet. Plants are obliged to communicate a lot, and they use different systems. The most important is through volatiles, or chemicals that are emitted in the atmosphere and received by other plants. It’s an extremely sophisticated form of communication, a kind of vocabulary. Every single molecule means something, and they mix very different molecules to send a specific message.
The idea that plants are intelligent is controversial enough, but you’ve gone one step further by claiming that plants are to some degree conscious…
It’s incredibly difficult to talk about consciousness, first because we actually don’t know what consciousness is, even in our case. But there is an approach to talking about it as a real biological feature: consciousness is something that we all have, except when we are sleeping very deeply or when we are under anaesthesia. My approach to studying consciousness in plants was similar. I started by seeing if they were sensitive to anaesthetics and found that you can anaesthetise all plants by using the same anaesthetics that work in humans. This is extremely fascinating. We were thinking that consciousness was something related to the brain, but I think that both consciousness and intelligence are more embodied, relating to the entire body.
So you can put a plant to sleep?
We are working to see if it’s possible to say that. It’s an incredibly difficult task, but we think that, before the end of this year, we will be able to demonstrate it.
As we learn more about the sophistication and sensitivity of plants, should we think twice about eating them?
It’s an interesting question. Many vegan people have written to me asking this. First, I think it’s ethical to eat plants because we are animals, and as animals we can only survive by eating other living organisms – this is a law that we cannot break. Second, it’s much more ethical to eat a plant than, for example, beef, because to produce a kilo of beef, you need to kill one tonne of plants, so it’s much better to eat directly a kilo of plants. The third point is that it’s very difficult for us to imagine being a plant, because for us being eaten is an ancestral nightmare, whereas plants evolved to be eaten, it’s part of the cycle. A fruit is an organ that is produced to be eaten by an animal.
So fruit is probably the most ethical thing you can eat, more so than, say, kale?
Maybe fruit is the most ethical, but you need to defecate on the ground afterwards, because otherwise you are breaking the cycle.