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Review of “Aspects of Plant Intelligence,” by Anthony Trewavas

Central to the uncovering of the harmony between biology, evolution, and Christianity is the idea of Life as an active agent in its adaptations to its changing circumstances.  In Chapters 2-4 in Christianity in Evolution I have presented evidence that animals are intelligent, can learn, and are able through rearrangements in their genetic and epigenetic networks to evolutionarily modify themselves.  But animals are only half of Life’s story on Earth; what of plants, the other half? I turn to plant biologist Anthony Trewavas[1] for his interpretations of the science of plants.  The following is a synopsis of his chapter in The Deep Structure of Biology (Reference below).
Plants are intelligent
It would never occur to most of us that plants are intelligent, primarily because they don’t move, as animals do.  The equation of “vegetable” with the term “brain dead” reflects our sentiments regarding intelligence in the plant world.  However, time lapse technology and striking advances in plant physiology, signal transduction (chemotaxis in E. coli is analogous), molecular biology, and cell-to-cell communication tell a strikingly different story.  In response to signals (light, heat, cold, wind, soil conditions, food sources, etc.), plants can change their various structures (leaves, shoots, roots, limbs, etc.) to individually optimize their foraging for resources.  In addition, plants are able to predict possible upcoming changes in resources (light, water, soil qualities, seasonal changes) and then alter their form, an action called phenotypic plasticity. Animals respond to such changes with movement, plants with phenotypic plasticity.
“It is in foraging for food that animal intelligence becomes a premium, and it is in plant foraging that plant intelligence comes to the fore.“ (p70)  We can perceive the processing of information by animals, but the time frames are much longer for plants, as time lapse technology makes clear. “As we acquire more knowledge about all sorts of behavioral characteristics of living organisms, not only are previous assessments of intelligence and behavior shown to be wrong, but the expanding view enlarges our perspective of life itself.”  (P. 71, emphasis mine)
Trewavas goes on to discuss the issue of intelligence, pointing out that the Latin root literally means to ‘choose between.’  He advances the idea that what we see as innate behavior of animals and plants “arose from learned, that is, intelligent, behavior in the first place, potentially by genetic assimilation.” (p72, more on genetic assimilation later)  He argues that organisms exhibit foresight “that allows organisms to come up with a behavioral solution to an environmental problem with minimal trial and error.  Improved behavioral modification enables the subsequent selection of genes and gene combinations… that allow the strategy to develop with greater rapidity, higher probability, or lower cost.  Consequently, evolution becomes much faster than mechanisms that require selection of random gene combinations, just as foresight reduces the time required for successful behavior.” (p73)  He goes on to argue for intelligence in bacteria, protists, genomes, immune systems, swarms, and metabolic networks.  He concludes that “Apart from the higher animals that use the centralized activity of the brain to process information and in which classical intelligence is located, all other biological systems possess a decentralized intelligence that is a consequence of behavior by the whole system.” (p.79, emphasis the author’s)
Plants are active, not passive
The author proposes that “Two perceptions of plant growth and behavior need to be distinguished.  A common passive view is that plants grow according to a predetermined genetic program with  rates determined merely by provided resources…The active view of plant behavior is in complete contrast.  For plants facing competition from neighbors and from other organisms in a variable abiotic environment, intelligent adaptive behavior is a necessity, not a luxury.” (p 80-81)  He documents numerous strategies , such as exploratory speculative growth of shoots and roots, variations of leaves to capture maximum light, and root strategies to maximize water and minerals in highly variable soils.  “Decision making about phenotypic change involves in some way the whole plant and is, thus, decentralized.”  (p82)  Decentralization is essential in a class of organisms constantly grazed upon by animals.
Plants are networks
Plants, being both social and modular, are interactive networks of leaves, stems, roots, flowers, and seeds.  Such networks evaluate the whole of the environment, and the whole network modifies itself to any environmental change.  As a result, there is “a very complex mixture of communicating signals moving throughout the plant individual.” (p 83)  Signal transduction is the conveying of information about the environment via complex biochemical networks.  As a result, plants “perceive their environment in considerable detail, make meaningful assessments of that information, and institute adaptive phenotypic responses designed to improve competitive ability and resource acquisition…Intelligence is an emergent property that results from complex interactions between the tissues and cells of the individual plant.” (p.93)
Plants are agentive
Throughout the article Trewavas discusses various agentive actions of plants.  For example, plants are territorial, taking over available space and denying it to others.  But plants sense their own kind and avoid competing with them.  They in addition possess complex self recognition systems.  Plants make complex decisions on how and where to vary phenotype to garner scarce resources.  Plants conduct sophisticated cost/benefit analyses in their quest for light, food, and water.  Plants are capable of foresight; they can sense the future possibility that a competitor might overshadow them, and they adapt system-wide in response.  “Foresight of future water availability also institutes characteristic morphological changes in anticipation and preparation…programs indicate an ability to anticipate environmental change, even though it may not happen during the lifetime of the individual plant.” (pp. 89-90).  The author goes on to cite extensive evidence that plants in general learn and remember.  Trewavas leaves no doubt that plants, like animals, actively contend with life’s ever changing circumstances.
Plants, Intelligence, and Evolution
Trewavas notes that intelligence is intrinsic to all biology, from bacteria to plants to animals.  Bacteria use quorum sensing, plants decentralized intelligence, and animals central nervous systems.  Bacteria learn by horizontal gene exchange, individual cells through computation, and higher animals by complex neural networks.  “Underpinning all the forms of intelligence…is a network whose connection strength can be altered, enabling control of information flow and memory to be constructed.” (p. 95)  Why, the author asks, is intelligence so widespread?  Because it is the more intelligent who will forage the most effectively and will be naturally selected.  Intelligence will beget more intelligence.
The author continues, “There are currently at least two kinds of evolutionary models relevant to this discussion. The first, the neo-Darwinian view, sees overproduction, random genetic variation, and differential survival as the basis of evolution.  The second…places behavioral changes as the first response to environmental shifts…Those that adapt most efficiently and are, thus, best able to master the current changes in the environment will experience preferential survival.” (p. 97-98)  Through inbreeding of the more intelligent, the new and more efficient behavior becomes genetically fixed, a process known as genetic assimilation.  In other words, “Whatever genes the successful organism possesses go along for the ride…The very refined and complex forms of innate behavior found in reproductive rituals in animals and birds must surely originally have been learned behavior that has now been genetically assimilated.” (pp. 98-102, emphasis mine)
The author concludes that “Genetic assimilation is initiated by changes in behavior, and, (in plants) behavior is expressed as phenotypic plasticity, which I have indicated is intelligent behavior…The evolution of intelligent behavior found in all forms of life, thus, becomes a central theme in the evolution of life itself.” (p. 102, emphasis the author’s)

[1] Trewavas A. “Aspects of Plant Intelligence,” in The Deep Structure of Biology-is Convergence Sufficiently Ubiquitous to Give a Directional Signal?” Simon Conway Morris, Ed. (2008) Templeton Press, West Conshohocken, Pa.

Anthony Trewavas is a professor at the University of Edinburgh.  He has special interests I plant-cell signal transduction and plant behavior.  He has published over 220 papers and two books.  He is a fellow in a number of professional societies.