Thinking Like a Plant

 
Cameron Smith has just published the second article on plants and intelligence. You can find it on page 6 in the "Ideas" section of today's Toronto Star [Can plants think? This slime solved a maze].

In today's article he mentions my criticism of what he said last week. He's referring to the idea that plants have intelligence when he says,

There are critics of such claims, however. For instance professor Laurence Moran of the University of Toronto's biochemistry department took exception to last week's column in his blog, saying systems biology "can be a very useful approach to a problem," but, "turning it into a religion isn't going to help."

He complains about too much rhetoric and not enough "real data." His blog is at http://sandwalk.blogspot.com. Scroll down until you come to "Junk DNA in the Toronto Star."

Here's the link to that posting [Junk DNA in the Toronto Star].

The main point of my article was to point out the scientific inaccuracies in Cameron Smith's description of junk DNA. I explained that Smith was falling into the same trap as many science journalists—he was bamboozled by the hyperbole and self-promotion that scientists (and press officers) engage in to make their work seem far more important than it really is.

My criticism is part of a bigger campaign, one that puts more onus on science writers to sort out the wheat from the chaff and report on real science for a change [See The Benefits of Science Blogging]. Cameron Smith did not do that in his first article but he has taken a small step in the right direction today. At least he mentions that there are some scientists who are skeptical of the idea that plants can think.

It's easy to get confused here. Nobody is questioning the idea that plants can sense and respond to their environment. Bacteria can do that as well. They have chemical sensors in their membranes that detect certain chemicals and these sensors are connected to the flagella that propel bacteria through their liquid environment. The sensors direct the bacterium to move toward higher concentrations of a favorable chemical (and away from dangerous ones).

Bacteria are single cells. If you call that sort of thing "intelligence" then the word intelligence loses all sense of meaning. We could easily rig up a little electric toy car that finds a heat vent in the floor but we would not (I hope) call the car "intelligent."

Admittedly, plants are a bit more complicated than bacteria so their mechanisms of regulation and feedback are sophisticated. But let's not get confused about the difference between sophisticated feedback circuitry and "thought" which is a trait that one usually associates with meaningful properties of intelligence.

That's exactly what Cameron Smith seems to be doing when he says,

It shouldn't come as a surprise that there are reputable scientists making the controversial claim that plants have memories, that they can store and interpret data, that they can integrate information, that they can identify relationships between dissimilar entities, and that they can analyze and even predict – as, for instance, when the mayapple, a simple white flower that is a forest-floor perennial, makes choices about future branch and flower formation years in advance.

A wealth of scientific detail supporting these claims is available in Communication in Plants, published last year by Springer-Verlag in Germany. The book is a collection of scientific papers edited by professors in Germany and Italy. Since it sells for $234.50 in Canada, looking for it in a university library may be a better option than buying it.

It may be stretching language to say these characteristics demonstrate primitive intelligence. Nevertheless, they point toward a capacity to perform tasks typical of what we call intelligence.

It is, indeed, stretching the point to ask "Can plants think?" That is not responsible science journalism, in my opinion. There are plenty of interesting things to write about when it comes to explaining how plants can interact with their environment. I'm sure there's an audience out there who would like to know how the slime mold finds the best route through the maze, for example (see the opening paragraphs in the article).

The original paper referred to in the newspaper article is Nakagaki et al. (2000). In 2001 Nakagaki published a short review paper describing the experiment.

The figure on the right is taken from that second paper (Nakagaki, 2001). The figure shows the slime mold, Physarum polycephalum, spreading out on the surface of an agar plate looking for food (a). In part (b) you see the leading edge of the spreading disk. As you can see, in search mode the cytoplasm is relatively unorganized.

In (c) you see a plasmodium that has found several sources of food. These food sources are oak flakes (white blobs) that are scattered on the surface of the agar plate. When the plasmodium finds an oak flake it surround it and sets up channels to bring nutrients back to the main body. As you can see, the shape of the plasmodium changes as it contracts those unsuccessful extensions in order to make a superhighway of cytoplasm to the food source.

The slime mold will also behave like this in a maze. It spreads out into all possible paths in the maze looking for food. When it finds a food source, it contracts all the dead-end extensions in order to concentrate on a single extension via the shortest distance to the food. This is what is meant by "intelligence" but it's not much more complicated than the bacteria who locate food by connecting their chemosensors to their flagella.

Nakagaki is very impressed with this behaviour. Here's what he says in the abstract to the second paper.

Even for humans it is not easy to solve a maze. But the plasmodium of true slime mold, an amoeba-like unicellular organism, has shown an amazing ability to do so. This implies that an algorithm and a high computing capacity are included in the unicellular organism. In this report, we discuss information processing in the microorganism to focus on the issue as to whether the maze-solving behavior is akin to primitive intelligence.

Nakagaki might be impressed but I don't know very many other scientists who would use this kind of language to describe a simple mechanical property—a property exhibited by most cells. (Incidentally, Physarum polycephalum is not a plant by any stretch of the imagination. Fungi, are not plants. Fungi are more closely related to animals than to plants. Physarum isn't even a fungus, as one of the commenters reminds me, it's a protist.)

There are two ways science journalists could approach this study (and other similar ones). They could reinforce the hyperbole and try to convince the general public that scientists had stumbled upon something new and extraordinary. Of course, in order to do this the science journalist would have to disguise the fact that the vast majority of scientists scoff at this sort of nonsense. That might convince the editors to publish a sensationalist piece that could sell newspapers.

The other approach would be to explain why such claims do not really make it into the mainstream of scientific discourse. There's a good reason why botany textbooks are not being rewritten to include chapters on plant intelligence. This kind of science journalism is much harder but potentially more useful since it teaches the essence of science, namely skepticism. Maybe the newspaper editors won't pay for such articles but that's another problem.

Cameron Smith is interested in the environment and he was written many wonderful articles on that subject. Today's article contains a warning for those who buy the concept of plant awareness. Such a person is Peter Harries-Jones of York University who accepts that plants demonstrate awareness. Harries-Jones is an anthropologist who has developed an interest in systems theory and ecology. This is the kind of "systems theory" promoted by Gregory Bateson. It's not systems biology, it's the religion that bears only a superficial resemblance to the the science.

In a paper delivered to a New Orleans conference in October, he [Harries-Jones] quoted Gregory Bateson, a pioneer in communication among organisms in ecosystems, to make the case that the first step in ecosystem collapse could be a breakdown of communication, "as a result of too much fragmentation of complex interactions ... This means," he said, "we should pay the closest attention to any changes in the response of living organisms to each other."

Paying attention to such changes is something that should interest even non-believers such as Moran – especially since a breakdown in communication may be already happening with bees.

Sorry, but a breakdown in communication is exactly what I'm witnessing here. A wide gap seems to have opened up between rational thinking and whatever passes for rational thinking among those who think like a plant. If that kind of fuzzy thinking continues then we will, indeed, see a collapse—not of ecosystems but of civilization.

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Nakagaki, T., Yamada, H. and Tóth, Á. (2000) Intelligence: Maze-solving by an amoeboid organism. Nature 407:470 [Nature] [PubMed]

Nakagaki, T. (2001) Smart behavior of true slime mold in a labyrinth. Res, Microbiol. 152:767-770. [Res. Microbiol.] [PubMed]