The central thesis of ‘The Revolutionary Genius of Plants,’ at least as presented by the marketing, is that plants are intelligent, behavioural agents. Unfortunately, the book falls short of providing convincing evidence for this, and a lot of the arguments are confused and contradictory.
Before I dig into my review, I want to make a few things clear. I am a neurophysiologist by training, and I’m very familiar with the plant intelligence literature. Both personally and professionally, I’m very sympathetic to thesis that plants are ‘intelligent’ systems. I mention this because I want to be clear that I criticize the book from a position of familiarity with the science, ultimately, agreeing with the thesis – not from one of dismissal, or undue scepticism.
Unfortunately, the book bumps into credibility problems almost immediately. As the opening chapter seeks to set the stage for showing plants are intelligent by focusing on evidence that plants exhibit memory, the author refuses to define either intelligence or memory and, in doing so, rather cheekily avoids commitment to any particular concept and sets up the precedence to dance around criticism by accusing critics of being too reductionist. This begins on the first page, where the author accuses the literature of avoiding an open conversation about plant intelligence, stating "When discussing plants ... other terms are usually used: acclimatisation, hardening, priming, conditioning, all of them linguistic acrobatics coined ... to avoid the use of the comfortable and simple memory" [Page 5, my edition]. This is an incredibly disingenuous statement: all the mentioned terms are, in fact, used throughout neuroscience when referring to animals, not just in discussions of plants. These terms each have a very specific meaning – some related to memory in a broader sense – others in reference to different computational principles. Acclimatisation, for example, refers to the tendency of a system (a whole organism, or a neuron) to reduce its response to (i.e, ignore) a continued stimulus – think about the way you tune-out the sound of an air conditioner that has been on throughout the day. These words are not used to avoid talking openly about intelligence – they are used because they have precise meanings, and in science precision of language is important.
The next few chapters focus on movement and mimicry in plants, and make some very similar errors as the above. For brevity I’m not going to call out each in succession – just the broader pattern; The Revolutionary Genius of Plants, at best, is very confused by scientific terminology and concepts. At worst, it’s wilfully misunderstanding.
As a short aside, the chapter on mimicry provides the perfect example for another issue with the book. It is beautifully illustrated – with lots of high-quality images printed in the text, but they rarely serve to enhance understanding. For example, in a section describing the ability of one particular species of plant to mimic the shape, colour, and pattern of the leaves of the plants around it would have been wonderfully served by images showing the actual mimicry, but there are none. At several occasions in the book I wished for a picture to illustrate or exemplify the point, but pictures – though nice – seemed inserted randomly, based on an i-stock image search of words on the page.
However, casual misuse of semantics is not my biggest issue with the first half of the book. For each topic covered, the author martials some very simple experimental evidence to prove plants exhibit some behaviour or other. I have no quarrel with these experiments (though most are very simplistic, and on greater thought, don’t quite prove the claims the author makes. Many I would consider supporting evidence, but not sufficient). My broader disappointment is that there is little attempt to probe into a deeper understanding of the topics. Instead, the text reads like a series of summaries of unrelated experiments, each paragraph trying to one-up the last in a competition of ‘See what weird thing plants can do?’ There is no synthesis, no drive to underlying principles, no attempt to ask how (in a mechanistic sense) or why (in a teleological sense) the observed phenomena can occur.
As an example, consider the mimicry phenomena described in the aside above. How does a plant ‘know’ what its neighbours look like? The author rather flippantly suggests that the plant may have a kind of visual system – that they are literally able to see the plants around them, derive from such a visual input the shapes, patterns, and colours of those nearby plants, and then transform this information into a set of instructions on how to achieve the mimicry. This is a fantastic claim – I should know more than most, my subspecialty of neurophysiology is the visual system – but it is made in pure speculation, with no further exploration of the implications, questions, or issues the theory brings up. I’ll spare the reader of my full thoughts on the hypothesis and I’ll admit I’ve not yet read the academic literature on the theory (I would love to be proven wrong in my scepticism), but the point of my criticism is the book should give a comprehensive (if not in as fine a minutiae as an academic report) view of the theory. A scientist writing a book for the public has a responsibility to present the science in a clear and accurate way, but this is something The Revolutionary Genius of Plants seems to have abdicated.
About halfway through the book, Mancuso gets on to building something of a unifying thesis – and here again we run into big trouble. The central argument of Mancuso’s thesis is that the main difference between plant and animal intelligence is one of distribution. Plants, so the claim goes, have distributed intelligence, while animals have intelligence centralised in a single organ, the brain. Already this is a gross oversimplification and a false dichotomy; Plants do indeed have functionally specialised organs: Roots, leaves, stems, and reproductive organs are all spatiotemporally distributed for certain functions and microenvironments – plants rarely grow photosynthetic leaves under the ground. Mancuso is aware of this, and posits that plant intelligence is centralised (See the cracks?) in the root system, a highly distributed network of cells that sense, integrate, and store information.
It is here that the comparison to the brain is at its most absurd, and most humorous; not in the least because I am reminded of a similar comparison that has played out in computer science, but in that case the brain is the distributed network. The fault of Mancuso’s argument is one of scale: it’s unfair to compare the distributed microarchitecture of a root system with the centralised macro-architecture of the vertebrate brain (To say nothing of the highly distributed macro-architecture observed in some invertebrates). Comparing like-to-like, both the roots and brain are relatively centralised organs, with highly distributed micro-architecture. Ironically, this seems to play better into the thesis of the book than the original claim, since a common axiom of biology is 'Similar form; similar function,' but that seems lost. Even more bizarrely, the bulk of the chapter on distributed intelligence – rather than building up a framework for interpreting the physiology of roots in a computational framework, something necessary to posit intelligence – focuses on distributed intelligence in animals (… with brains.) Ants and Bees are discussed, and I completely agree with Mancuso’s suggestion that they provide evidence for computational and intellect-ability in distributed system, it just seems a strange choice of evidence for supporting the hypothesis in plants. Now, I don't want to claim that there is no difference between plantae and animalia, or even that distribution of function isn't a difference - it's just nowhere near a vast a gulf or significant a distinction as presented here.
The remainder of the book takes a somewhat odd turn, by strangely re-defining intelligence. In behavioural sciences intelligence is usually broadly defined based on an animal’s ability to react to an ongoing situation – it is an ‘online’ process, and the property of an individual being. We don’t usually consider a dolphin intelligent because its shape allows it to swim through the water, even if we might describe the hydrodynamics of a dolphin as ‘intelligent’ or ‘clever.’ Dolphins are intelligent, but not in virtue of their shape. The remainder of the book, however, considers almost exclusively this kind of evolutionary optimization as ‘intelligent.’ One chapter, for example, describes in excruciating detail the author’s experience at a chilli festival, making the strange claim that chilli is highly intelligent for developing capsaicin, that has allowed it to a) ward of predators, historically, and b) become an international delicacy for humans, ensuring it’s cultivation and propagation. Claiming chilli is intelligent by virtue of its evolutionary development of capsaicin seems – to me – an incredible broadening of the term, and a frustrating choice in the face of so many genuine examples of plant intelligence in the literature that go unmentioned.
The discussion of this form of plant intelligence broadens into the concept of bio-inspiration – the idea that we can derive from nature engineering principles to solve problems. Gone is the pretence of discussing the ecological role of a plant and its capabilities, gone is the pretence of discussing the mechanisms by which a plant’s behaviour arises. With each new chapter, the focus shifts further away from plants as an intelligent being, and closer towards how we can utilize plants in technology. This is a bit of a kick in the teeth – I love both plant intelligence and bioinspiration. Both are extraordinary fascinating topics that deserve a much larger share of public consciousness. If the book was to be about bioinspiration, why the pretence of a focus on plant intelligence? And if the book was supposed to be about plant intelligence, why the shift of focus away? In mixing and confusing them, this book had done both a disservice.
I do think I know why. The one commonality I could detect among each chapter, is the author’s personal involvement in the projects mentioned. Rather than a scholarly work reviewing the whole field of plant intelligence, it’s most exciting discoveries and thought-provoking experiments, ‘The Revolutionary Genius of Plants’ is an extended CV – a grab-bag of the projects the author has had personal involvement in. Alone, each project is fascinating puzzle-piece in a broader literature, but collected together without the context, The Revolutionary Genius of Plants comes off more as an exercise in narcissism than a piece of scholarship.