We humans have a pretty high opinion of our place in the hierarchy of nature. We sit right atop the pyramid of life, above the other mammals and far above the plants. Yet as it turns out, flora is far more intelligent then we could have imagined.
Despite not having brains, plants are capable of gathering an extraordinary amount of information about the world they inhabit. Their complicated network of sensory receptors is not a nervous system per se, but it can detect sources of light, for instance, which allows plants to plan their growth and maximize sun exposure. Roots, meanwhile, can detect harmful minerals in the soil and reroute their growth. Many species can release chemicals to warn other plants about dangerous diseases or predators. Two saplings can even determine whether they are related and then decide not to compete with each other for resources. These abilities require sophisticated means of communication.
For Stefano Mancuso, all of this means that humanity needs to radically rethink its relationship with plants. In his new book, “Brilliant Green,” he lays out the case for approaching plants as fellow intelligent life-forms. Doing so, he says, will give us key insights to fields across the sciences, from botany to robotics.
Ideas reached Mancuso in Florence via Skype. Below is an edited excerpt:
IDEAS: How smart are plants?
MANCUSO: In general, you can say that plants are intelligent according to a specific definition of intelligence. In my view, intelligence is the capacity and the ability to solve problems. It isn’t just in animals or plants, it is something that can be found in all living organisms. Without intelligence, there is no way that organisms can evolve or survive, because everything has to solve problems to survive.
IDEAS: How can an organism without a brain be intelligent?
MANCUSO: Normally, people tend to link these two concepts: intelligence with having a brain. We need to have brains in order to be intelligent. But that’s only true for animals. There’s no evidence that you need to have a brain in order to be intelligent if you’re a plant. Just think about swarm intelligence. A single ant is one of the stupidest animals in nature — but a colony of ants shows an intelligence that is much more impressive.
In plants, you will never find a specific organ responsible for a specific function, like a brain. You will never find a couple of lungs or a stomach or some eyes. But this doesn’t means that plants don’t have these functions. They are able to breathe without lungs, they are able to digest without a stomach, and they can memorize things without a brain. They diffuse, across their entire bodies, what animals concentrate in single organs.
IDEAS: Can plants memorize?
MANCUSO: Retain information? Yes. Last year we published a paper demonstrating that it was possible to teach mimosa pudica, a small plant that closes its leaves immediately after you touch them. We succeed in teaching a group of mimosa plants that being dropped in a pot from a height of 10 centimeters wasn’t dangerous and that they had no need to close their leaves. After a few repetitions, they were able to discriminate between two stimuli: They closed when they were touched but didn’t after they were dropped. They were able to learn. Probably more interestingly, after leaving the plants for 40 days completely undisturbed, they retained the memory of the stimuli, so even after 40 days, they could discriminate between the stimuli. It’s a first level of memory and a first level of learning.
IDEAS: How do plants make these decisions?
MANCUSO: We don’t have a clear idea, which is why we are studying it further. We know that there is, in the roots, a specific region that is some sort of a command center. All the information about the environment is collected and, in some way, a decision about the direction of growth is made. We have no idea how they are able to organize the growth of the root apparatus in a nonchaotic way. The roots are huge, a tree may have more than 10 billion root apexes, it’s in the same order of complexity as the human brain. We have no idea how they organize the growth of something so huge. We know that each root apex has its own command center, but we have no idea about how they can organize this growth. We think it is some sort of swarming behavior.
IDEAS: This is fascinating, but why should we care whether plants are intelligent?
MANCUSO: Plants are a mine of new inspiration for science and technology. Every idea about man-made machines has been inspired by animals. Our machines, our cars and tools, have been inspired by animals. But plants are a completely different [muse]. They are networks, they aren’t hierarchic. They have no single organs: Instead, they distribute these functions throughout their body. So, there’s a lot to learn from plants, and there is a lot to build on, starting from the study of the plants.
IDEAS: What might a machine designed to think like a plant look like?
MANCUSO: Machines inspired by plants have no common center, for example. They are made by a big number of similar modules connected to each other. Just look at how a machine inspired by plants can be much stronger and difficult to damage. For example, when we built the Internet, it is something very similar to the roots of a plant. There is no common center, every node of the Internet has the same importance. This is a structure that is inherently solid. You can destroy 95 percent of the structure, and the Internet would still work. In principle, we can think about machines in the same way, this is the plant way.