Mancuso, Stefano and Alessandra Viola. Brilliant Green: The Surprising History and Science of Plant Intelligence. Translated by Joan Benham. Island Press, 2015.
This small book by an Italian scientist and science journalist makes the case that plants have been underestimated and that they have a kind of “intelligence.” They convinced me — but only for some definitions of intelligence.
The book begins with a survey of ideas about plants in the past. The three major monotheistic religions mostly ignore plants, though Mancuso and Viola point out that Judaism forbids the gratuitous destruction of trees and has a holiday to celebrate their new year. Most philosophers and scientists before the 20th century didn’t think much of plants either, but Democritus, Linnaeus, and Darwin suspected there was more in them than met the eye.
The authors soon build a dichotomy: are plants “social organisms, sophisticated and highly evolved like us” (p. 36)? Or are they “closer to the mineral world than to animal life” (p. 37-8)? Surely those are not the only choices. I didn’t believe either of these possibilities before reading the book, and I didn’t believe either of them when I finished the book.
Elsewhere in the book, however, Mancuso and Viola use a more reasonable formulation: “Intelligence is the ability to solve problems” (p. 126). They note the most obvious difference between plants and animals, that plants are stationary (at least for most of their lives). They are therefore subject to predation by herbivores and therefore cannot have centralized, specialized organs that an animal could eat and kill the plant. So, just as plants have a decentralized circulatory system without a central “heart” to pump fluids throughout their bodies, they also have a decentralized nervous system without having a central “brain.”
The middle of the book, which is the most informative, describes how plants solve problems in their lives, often by means analogous to what animals do. Mancuso and Viola demonstrate that plants have:
- a sense of sight
- a sense of smell
- a sense of taste
- a sense of touch
- a sense of hearing
- 15 other senses, including a sense of moisture and a sense of gravity
Plants also communicate. One part of a plant can communicate with another, such as when the roots tell the leaf openings (stomata) whether to open or not. Plants communicate with other plants, such as telling each other when an herbivore is near. Plants communicate with animals, such as when they provide incentives for their moving friends to pollenate them or spread their seeds.
Plants even sleep, a fact Linnaeus was one of the first to notice, but still not much is known about why they do so.
The book has a few egregious errors of science, which make it difficult to trust the authors when they make bold claims.
We know that the first single-celled organisms that appeared on the planet were algae — that is, the plant kind of living things. Through photosynthesis, they created the oxygen that enabled life to spread over the earth. This included the emergence of eukaryotes, or animal cells. (p. 29)
No, both plants and animals are eukaryotes. (The term refers to organisms with cells having a nucleus and organelles, not to the cells themselves.) Organisms with simpler cells, such as bacteria, are called prokaryotes.
It’s like saying that if 100 is the total weight of everything alive, according to various estimates, between 99.5 and 99.9 percent is composed of plants. Or to put it another way all living animals — humans included — represent only a trace (a scant 0.1 to 0.5 percent). (p. 40)
This seems to be saying that all living things are either plants or animals. What about fungi, protista, bacteria?
… [T]he vectors are bats (cheiropteroi in Greek), which are used to carry pollen from many American desert cacti, such as the Joshua Tree. (p. 109)
The Joshua tree is a yucca, not a cactus.
Despite some overblown claims for plant intelligence and a few errors, this book is worth reading for some solid information about plant capabilities, some of which have only recently been discovered.
Disclaimer: Island Press sent me a free copy of this book as part of their “blind date with a book” promotion.