[~ 10 minutes]

Listening to: One Republic, Wherever I go

“We are tree-herds, we old Ents. (…) Some of my kin look just like trees now, and need something great to rouse them; and they speak only in whispers. But some of my trees are limb-lithe and many can talk to me. Elves began it, of course, waking trees up and teaching them to speak and learning their tree-talk. They always wished to talk to everything, the old Elves did.”

J. R. R. Tolkien, The Two Towers

To the best of my knowledge, there are no ents in New Zealand. There is, however, a tree steeped in Maori myth called Tāne Mahuta. The actual tree is a kauri (Agathis australis); the mythic Tāne Mahuta was a son of the gods of earth and sky, and the only one who managed to break his parents’ stifling embrace by pushing them apart, so the world could exist between them. Considered the Lord of the Forest and creator of humankind, he is commonly pictured as a tall man bridging —and indeed sustaining— the gap between the sky vault and the earth, legs firmly planted on the ground (or rooted in the sky).

Lately I’ve been thinking a lot about trees. Paradoxically enough, it all began because of a book I have not read (yet): Peter Wohlleben’s bestselling title The Hidden Life of Trees: What they Feel, how they communicate — Discoveries from a Secret World.

A science-oriented book by a German forest ranger might strike you as entirely unrelated to ents, talking trees or primeval Maori forest deities, and two weeks ago I would’ve agreed with you. Then I read this review on the NYT, and I changed my mind…

Apart from talking about the book itself (which sounds intriguing and worth reading), the article mentioned that some biologists are concerned about the language Wohlleben uses, because he blatantly humanises trees— and does so on purpose, using a “very human language” (in contrast to an emotion-less, scientific language) so as to let the reader imagine what a tree might feel.

From those two paragraphs in the review I glimpsed two opposing world-views, that one might jokingly describe as: the stuffy scientists with their jargon and insistence on linguistic hair-splitting and accuracy, versus the dirt-under-my-fingernails forest ranger that believes in telling people that trees inwardly yelp Ouch when their bark tears, or that they talk among them, because such concepts are easier for readers to grasp.

The clash between these two perspectives goes well beyond Wohlleben’s book, and may be condensed into a single question:

should we or should we not humanise trees?

First though, let me bring your attention to a slight detail I find quite revealing: it’s all about the trees. Not the shrubs, not the grasses, not the aquatic plants or any other plant life-form other than trees.

The plant way of being in the world: more akin to a colony of (nigh)pluripotent cells where the individual, ie the un-dividable entity, does not quite exist.

Why? I am quite convinced it’s because trees are the plant forms we can most easily imagine as human-like.

And oh, don’t we love thinking about things as human-like, be they stars, trees, bugs, or cars. This is not entirely our fault; it’s just the way our minds are made. We come equipped with a single, human operating system (OS), and have no other models available: there is no way to install, say an earthworm’s OS in our brain* and feel what being a worm is like.

*…’twould be tricky indeed, as earthworms have no brains.

We are stuck with being human, and experiencing the world as humans, just as a jellyfish is stuck with its own modality of feeling and existing in the world.

Plants present a further complication that appears obvious when you look at the evolutionary relationship between humans and plants:


Considering that our last common ancestor was single-celled and lived in a time when all living forms were still under water… well, you might as well try to empathise with an amoeba. And despite the fact that, just like Tolkien’s elves, we love talking to animals and plants, unlike those in Middle Earth our trees are not sleepy humanoids with an excruciatingly slow sense of time and a few funny photosynthetic quirks.

Plants, I’m afraid, are like beings from another planet, alien in their utter strangeness when compared to ourselves. It’s impossible to conceive their existence according to human categories: they must be met and described on their own plant terms.

 This means that we are entirely, biologically incapable of imagining or understanding what a tree is feeling, and that we will always be. And no amount of talking about trees in human-like terms will ever change it, no more than flapping your arms will help you fly off a cliff.

“Mmmmhmm… nope. Not working.”

In fact I find it rather hilarious, that we openly acknowledge how hard it is for (wo)men to empathise and understand what the opposite sex of the same species is feeling; but that we somehow believe ourselves capable of imagining what a birch feels!

You may be thinking, well, if we’re never going to understand them anyway, any attempt to study them is pointless, right?

Wrong. Nothing stops us from trying to understand the mechanisms they use to live as plants: how they communicate, feed, grow, defend themselves from predators… Just as you can learn much about swimming just from theory, regardless of whether you’ll ever do it, we can learn much about how trees live, without having the faintest idea of what being a tree is like.

Understanding theory versus living practice; science versus embodied experience.

And this is fine. I can live with my limitations, as long as I acknowledge them, instead of fooling myself into believing I can somehow feel like a tree, or vice-versa. Which is why, as a biologist, I think scientific texts should avoid humanising trees, basically because it’s not fair to the trees’ own way of being alive.

You may now be thinking, isn’t it a bit harsh as a judgement? If humanising trees gets readers to empathise with them and grow to care for them, isn’t that a great success? Aren’t scientists making too big a fuss about nothing?

To which I’d reply: perhaps in part, yes. Science has grown allergic to certain plant-related analogies and metaphors, and it may sometimes exaggerate in its refusal to use them.

Why has this come to be? Well, I suspect it’s mostly because of how we used to classify living beings, at least since Aristotle: with the scala naturae, that great chain of being in which rocks were the lowest of the low, then came plants, then animals, then humans (… then angels and God). This linear scheme that considered a single model throughout the whole ladder (merely becaming more ‘alive’ as we climbed up) encouraged establishing analogies between eg. plant sap and animal blood, and even imagining that trees might be hiding something like a heart among their leaves.

Scala taken straight out of a eighteenth century book, Theologia Rationalis Ad Hominem, & ex Homine…, freely available via GoogleBooks.

Of course none of it was true. And the more we discovered about how fundamentally different plants were with respect to animals, natural philosophers then scientists grew increasingly wary of analogies between animals and plants.

Misapplying animal categories to plant processes, ’twas understood, did a disservice to both kingdoms, which we should try to comprehend on their own terms.

(Incidentally, this is one of the reasons why the field of plant neurobiology has been criticised by some within the scientific community: because they feel that the name neurobiology sort of (mistakenly) insinuates the existence of neurones, brains, and a nervous system akin to that of animals. Indeed this stubborn refusal to draw analogies between animal processes and plant processes might be at the roots of the huge knowledge gap concerning information processing & integration systems in plants, which are only now being discovered as amazingly sophisticated beings and, yes, intelligent too, if by that we mean highly proficient at solving problems. In the end, it all comes down to the simple matter of definitions: how we define intelligence, learning, memory, and so on.)

In a (simplified, thus simplistic) nutshell: scientists reached the conclusion that no valid analogies could exist between plants and animals, and so decided to ban them all from plant-related scientific discourse.

There is, however, at least one tiny problem: that is, that we learn through analogy and metaphor. These are some of the most basic and powerful tools at our disposal to make sense of the world.

One should never underestimate the power of a good analogy.

A well-chosen analogy can make the difference between an epiphany of understanding and the dark fog of incomprehension, in all fields of human endeavour, as they help us comprehend the unknown by comparing it to familiar processes we do understand. And if our brains are thus wired, is it not rather absurd, to entirely forgo this most useful skill in our cognitive toolbox?


Some scientists warn, however, that there’s a dangerous process lurking in our metaphoric tendencies. Barber & Barber defined it beautifully as the “Principle of Metaphoric Reality”, wherein “the distinction between representation and referent —and between appearance and reality— tends to become blurred”.

That is: we may end up muddling the two terms we are comparing/ juxtaposing. One day trees are straight and tall like the brave warriors in our village, and seven generations later the trees have become the tall warriors of our village, and nobody is quite sure anymore whether it’s just a way of speaking, or if warriors truly became trees centuries ago.

This, of course, is fine for myths and imagination and literature, but here we’re talking about science. And science is wary of metaphors; most of all, of anthropomorphic metaphors and their slow (or fast) slide into metaphoric reality, and with good reason.

Metaphor becomes an ambiguous process that straddles the thin line dividing confusion from clarity… and clarity from confusion. Sometimes it helps illuminate the true nature of things, but other times it blurs and obfuscates reality.

Establishing certain analogies between humans and trees, applying human categories to trees… is not real. It does not describe nor encapsulate what the tree is feeling or experiencing.

It can doubtlessly help us ’empathise’ with the tree; we are much quicker to grasp an expression such as “trees talk”, rather than the scientifically correct “trees communicate”. And statements such as “trees suckle their children” do push us head-over-heels into caring about them.

Now, I strongly believe caring about plants is a beautiful, wonderful thing, and that we should certainly encourage and nurture such sentiments. I’m also interested in plant rights, which I find fascinating and probably also a necessary step we must take in the future.


I fail to see how thinking about trees as if we lived in Tolkien’s Middle Earth, as if our trees were humans in disguise who feel in the same way as we do, is going to help them, or us. Is it really going to do any good, having people seriously believe that plants feel pain just as animals do?

(… they don’t. What kind of masochistic nature would have plants feel animal-like pain all the time —leaves munched and trampled, branches torn, roots eaten…— when it serves no evolutionary purpose? Pain as we know it is for individuals whose existence is severely threatened by injury. But plants are not individuals: they are closer to clone colonies!**)


Falling prey to such illusions is a real danger, most acute when metaphors are used in texts that are considered scientific. Tree-like men & human-like trees belong in myth, and in literature, and in poetry, but they don’t belong in science, unless you state clearly that it’s a metaphor and not an accurate description of a tree’s experience.

If the price of easy ‘tree-mpathy’ is the misconstruction of a tree’s own truth, then isn’t our caring based on lies?

Isn’t it actually rather narcissistic, to project our own way of existing and feeling onto beings that have they own way of existing in this world? (Some researchers think so.) Aren’t we fooling ourselves into believing we can feel empathy towards trees, when it is precisely trees that demonstrate the utter impossibility of empathy ever existing between humans and plants?

I have not read Mr. Wohlleben’s book yet, so I cannot say whether it uncritically veers into Tree-mpathy Land, or if it frames its metaphors in a more careful and accurate way. I myself do use tons of metaphors in ways that are more poetic than scientific (eg. “frankincense resin as tree’s blood”), but I try to steer clear from using them in ways that would have you think trees are just like people, because they are not.

And, at least until I meet an ent (or an elven-taught talking tree), whether in New Zealand or elsewhere, I’ll carefully refrain from framing a tree’s existence as nothing but quieter, greener version of human experience.


**A note on plant-specific pain

Pain as we animals know it is linked to a specific kind of nerve cells we call nociceptors; there are several kinds of nociceptors (mechanical, thermal, chemical…) and each responds to different kinds of stimuli.

Plants have no nerve cells (recall their intelligence is not linked to a nervous system like that of animals), and thus have no nociceptors. That does not mean they don’t have senses (they do; quite a few, actually), but they have developed their own kind of sensory cells and signalling. And of course we have no idea as to how a being with no brain actually experiences what it is sensing. And there is no proof whatsoever that a plant’s ‘subjective sensory experience’ of something that an animal would perceive as painful, is felt in the same way.

The fact that they’re certainly sentient beings, and may be aware of their surroundings (and even anaesthetised!), goes against seeing them as nothing but inert green things we can blithely mistreat. But it doesn’t automatically translate into having to treat them as we would an animal.

I haven’t found much on “plant-specific pain” on scientific journals yet; the most recent and complete article I’ve come across is actually freely available online, it’s relatively concise and pretty interesting, so if it’s something that interests you I’d definitely recommend that you check it out:

Grémiaux, A.; Yokawa, K.; Mancuso, S. and Baluška, F. Plant anesthesia supports similarities between animals and plants: Claude Bernard’s forgotten studies. Plant Signal Behav. 2014; 9: e27886.




Just in case you didn’t click at the ‘right’ time, here’s the link to the NYT review (Jan 2016), and to the Amazon link to Mr. Wohlleben’s book The Hidden Life of Trees. As soon as I can get my hands on a copy and read it, I’ll hopefully share with you my opinion on the book 🙂

The Tolkien quote is taken from the chapter Treebeard; for references concerning the great Tāne Mahuta, you may browse the digitised version of The Coming of the Maori (1949); a visual representation of this divinity with feet rooted-in-the-sky can be seen here.

The fact that trees are given special consideration among plants may be ascertained in many ways; if it’s myth&religion we’re talking about, one good example may be Mircea Eliade’s chapter devoted to plants in his Treatise on the History of Religions (vol II), where he mostly (though not exclusively) talks about trees: sacred trees, cosmic trees, micro-cosmic trees, inverted trees, knowledge trees, tree marriages, etc. An entirely different text that analyses the changing relationships between humans and the natural world and devotes a chapter to trees as distinct from other plants (and more easily humanised in our thoughts!) is Keith Thomas’ Man and the Natural World: Changing Attitudes in England 1500-1800 (Penguin Books, 1984).

On the importance of analogy/metaphor, let me quote a few passages (because I find the subject fascinating) from Gregory Feist’s The Psychology of Science and the Origins of the Scientific Mind (Yale University Press, 2006):

“Analogy is one of the more ubiquitous ways the brain takes sensory experience and gives it meaning. Indeed, in the history of cognitive science the concept of analogy and metaphor has been one of the more central mechanisms answering the (…) question of how new knowledge is possible. (…)”

“Metaphor is closely related to analogy in that it, too, involves applying similarity from an old source to a new target and in this sense many metaphors are analogies. The essence of metaphor is an “as if” comparison—I am going to think about X as if it were Y. Some scholars, in fact, have argued that metaphor is the broader of the two concepts (…). By applying one phrase or idea to another different one that is not literally the same, we again make the unknown known. (…)”

“Steven Mithen (…) has argued that metaphor is an essential and rather unique quality of the modern human mind, and it becomes more and more frequent with ever-increasing cognitive complexity.”

(all italics and bold are mine)

Or you can also go watch James Geary’s TED talk, Metaphorically speaking. I gotta get my hands on that guy’s book…

The Principle of Metaphoric Reality is explained in Wayland Barber, E. and Barber, P. T. When They Severed Earth From Sky: How the Human Mind Shapes Myth (Princeton University Press, 2006), that establishes parallels between our linguistic minds, and our mytho-poetic (myth-making) tendencies.

Analogies in plant-related science & the great chain of being, two sources come to mind: the book by Susannah Gibson, Animal, Vegetable, Mineral? How eighteenth century science disrupted the natural order (OUP, 2015) (of which a review in Spanish, alas, may be read here); and an article by M. Barker (2002), Putting Thought in Accordance with Things: The Demise of Animal-Based Analogies for Plant Functions. Science & Education 11: 293–304.

On the impossibility of empathy towards plants, see Michael Marder (2012). The Life of Plants and the Limits of Empathy. Dialogue, 51, pp 259-273 doi:10.1017/S0012217312000431 (freely available on the author’s website). By the same author, there’s a nice article about plant rights, too (“Should Plants Have Rights?” The Philosopher’s Magazine, 62, 2013, pp. 46-50).

On plant intelligence, and the description of plants as “aliens”, I am inspired by the books by Prof. Stefano Mancuso (the only one published in English is Brilliant green: The Surprising History and Science of Plant Intelligence, by Island Press, 2015). For those of you who might’ve not read it, here’s an exhaustive article by Michael Pollan on The New Yorker on the subject of plant intelligence, The Intelligent Plant.


The tree of life image, which I’ve tailored to suit my needs so it illustrates better my point, is taken from Tree of Life Web Project.

The scala naturae image (edited again) comes from a book published in 1703 by a certain “A. R. P. Juvenalem Annaniensem”, Theologia Rationalis Ad Hominem, & ex Homine (…). It’s freely available via GoogleBooks.

All other pictures are from Yours Truly; if you want to use them, just let me know!



One thought on “Humanising trees: how much is too much?

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