Plant agency

This article is one of a series investigating a 'new biology' that gives full consideration to biological agency and its relationship to human agency. These articles are introduced in the article on biological explanation which considers the forward-looking biological explanatory emphasis on ends, goals, purposes, functions, and agency.  Much of the discussion revolves around the scientific appreciation and accommodation of real (genetically inherited) purposive (teleological, teleonomic) goal-directedness (agency) that is a universal distinguishing feature of life. The series also discusses the nature of biological classification and the way we classify 'everything' in our worldviews and modes of representation.

Human agency is a limited, conscious, and highly evolved form of biological agency. While it is currently conventional to treat biological agency as a human creation - the reading of human intention into nature - this website explores the claim that it was biological agency that gave rise to human bodies and human subjectivity - that, in this temporal sense, biological agency is prior to human agency.

The suite of articles exploring biological agency ranges across topics in theoretical biology and the philosophy of biology, including:

Processes - how biology is more concerned with process than structure or things.
Synthesis and analysis - the biological legacy of analytical reductionism.
What is life? - the crucial role of organisms and their agency agency in determining purpose, values, and what it is to be alive. How agency gives meaning to biological structures, processes, and behavior and must therefore take precedence in biological explanation.
Biological axiom - how this biological principle establishes the necessary behavioral (agential) conditions for all life as the universal, objective, and ultimate biological goals that give organisms - including their structures, processes, and behaviors - biological meaning.
Purpose - the history of the notion of purpose (teleology) including eight potential sources of purpose in biology.
Biological agency - as an account of the nature of biological agency.
Human-talk - the application of human terms, especially cognitive terms, to non-human organisms.
Being like-minded - the way our understanding of the minded agency of human intention is grounded in evolutionary characteristics inherited from biological agency.
Biological values - the grounding of biological values, including human morality, in goal-directed organismal behavioral propensities that express a universal behavioral orientation or perspective on existence (biological normativity).
Evolution of biological agency - the actual evolutionary emergence of human agency out of biological agency.
Plant sense, Plants make sense, and Plant intelligence addressing the rapidly developing research field of pre-cognitive agency in plants.
Biological hierarchy - the explanatory problem of levels, scales, and perspectives in biology.
The organism - the case for an organism-centered biology in which organisms as biological agents are the foundational functional units of biological organization.
Structures, processes, and behaviors - an introduction to biology that avoids the confusion of 'levels of existence'.

The biological axiom establishes the necessary behavioral (agential) conditions for all life. These are the universal, objective, and ultimate biological goals that give structures, processes, and behaviors biological meaning. Without at least an implicit understanding of these goals, biological explanations are an incoherent collection of unrelated facts so, in this sense, agency and function take explanatory precedence in biology. The structures, processes, and behaviors that make up the subject matter of biology may be compared in terms of both their structural-evolutionary history and functional equivalence.

The internal processing required to generate the organismal behavior summarized in the biological axiom can be conceptually framed as biological cognition. On this understanding human cognition is a species-specific and highly evolved form of biological cognition. Theoretical biology does not have a terminology to distinguish between structurally different but functionally equivalent forms of biological cognition. It therefore resorts to the terminology of human cognition (as cognitive metaphor). Though word meanings cannot be changed at will, in science it is possible to refine categories and concepts to better represent the world.^[73] 

Organisms demonstrate biological agency as the universal behavioral propensity to survive, reproduce, adapt, and evolve (biological axiom). Agency is an inherited life-defining characteristic that is part of the evolutionary continuity of all living things. As autonomous biological agents acting on, and responding to, their environments they have the capacity for both short-term sensory, and long-term genetic information exchange with their surroundings. Three articles extend this general theme into the realm of plants and sensory systems: plant agency introduces the unpopular notion of plants as agents; plant sense explores the ways that plants sense their environments, using the human senses as a point of comparison; and plants make sense describes how, as human agency evolved out of biological agency, the evolution of human senses was influenced by plants.

Introduction

Plant agency, like all biological agency, is expressed through the structures, processes, and behaviors of autonomous organisms whose activity is unified in the objective, universal, and ultimate behavioral propensity to survive, reproduce, adapt, and evolve. This goal-directed behaviour is most effectively understood and explained from an evolutionary perspective, as a study of comparative agency, with emphasis on those aspects of biological agency that are unique to plants.

Agency

We recognize agency in the goal-directed activities of agents.

In the living world it is organisms^[2] that most obviously express autonomous biological agency since their structures, processes, and behaviors are united in the propensity to survive, reproduce, and flourish (biological axiom). Though organisms exhibit a wide range of proximate behaviors, it is these goals that are universal, objective, and ultimate: universal because they are expressed by all living organisms; objective because they are a mind-independent fact; and ultimate because they are a summation and unification of all proximate goals. The emergent goal-directed properties of biological agency arose in nature in a naturalistic and causally transparent way (inherited variation with environmental feedback): there was no necessity for backward causation or the intentions of either humans or gods.

The evolutionary emergence of the entire community of life has been a process of adjustment (self-correction, adaptation) of autonomous biological agents to their internal and external circumstances in relation to these goals. In this process they have been constrained by their surroundings and the inherited species-specific configurations of their structures, processes, and behaviors.

In biological systems, it is the differentiation into structures, processes, and behaviors – of species and other taxonomic groupings – that is of special biological interest. How did they arise, and how efficient and effective are the many agential ‘strategies’ employed by organisms to attain the same ultimate biological goals?

We recognize plant agency in the same way that we recognize all biological agency – as autonomous flexible behavior acting on, and responding to surroundings. Plants have no nervous system or brain and so this behavior is mindless but, being goal-directed, it is, nevertheless, purposive.

The study of plant agency is not only of scientific interest – it also gives us a more informed perspective on the relationship between plants and people and, indeed, the relationship between plants and all other organisms.

Elements of agency

The articles What is life? and biological agency discuss in greater detail what is meant by ‘biological agency’ and how it is biological agency that distinguishes the living from the inanimate and dead.

The introduction, above, pointed out that agential behavior in biology is expressed most clearly in the autonomy of individual organisms whose structures, processes, and behaviors are united in the attainment of common goals.

The notion of agency still needs a little more explanation.

Autonomy

Organisms are part of a universal physical continuum but within this frame they express an independence of behavior that humans have recognized by individuation – the recognition of a distinct entity or individual. In everyday language a living individual (organism) is, for simplicity, called a ‘self’.

Agency is expressed through actions (behavior): but it helps to be more specific about the origins of this behavior. Actions might arise internally as an ‘acting on’ – say, behavior relating to food or a mate. It might also be initiated externally as a ‘responding to’ – say, the avoidance of a predator. However, the interplay between internal and external factors is complex, and in both these cases the agential behavior is then a consequence of internal processing. This might seem a trivial observation, but it is elevated here to being an ‘agency principle’ because organisms can be mistakenly treated as either inert matter on which the environment acts (like an acid on litmus paper), or inflexible selves like a kettle boiling water. In the causal process organisms are neither passive receivers, nor indifferent initiators – they are more like filters in a physical continuum. The significance of all this will become apparent later.

Agential behavior is n expression of the  tension between organismal internal requirements (behavioral propensities or ‘needs’) and both the internal and external constraints on these requirements.

Sensory systems

Agents are not passive; they are units of action and interaction. For an organism to act on, and respond to, its surroundings there must be an exchange of information between itself and its environment. As open and dynamic agential systems, organisms express their autonomy by regulating and integrating their flows of energy, materials, and information and, in this way, they are ‘self’-building, ‘self’-reproducing, ‘self’-regulating, and ‘self’-correcting (adapting).

This interchange is a necessary condition of agency, and it engages critical organs and systems of communication – the sensory system. For there to be discriminatory interaction between a biological agent and its conditions of existence it must have a condition-sensitive interface. This is the organism’s sensory system. Even mindless living organisms, like plants, have the capacity to discriminate between the objects and processes of their inner and outer environments in relation to the ultimate conditions of the biological axiom.

We are accustomed to the idea of information exchange related to the human senses, but all autonomous organisms engage in a ‘dialogue’ with their circumstances by employing a wide range of communication tools.

For a full description of the plant sensory system see the article on plant sense.

Biological axiom

Organisms are discrete and autonomous units of matter that act on, and respond to, circumstances that threaten or enhance their existence. They display flexible and goal-directed behavior that has a propensity for survival, reproduction, and flourishing (referred to here as the biological axiom). These are the objective, universal, and ultimate goals of all organisms whose structures, processes, and behaviors play a  subordinate and supportive role in the attainment of these goals. These goals are: universal because they are expressed by all organisms; objective because they are a mind-independent empirical fact; and ultimate because they are a summation and unification of all proximate goals, including those of minded organisms.

For individual organisms, these conditions are temporary because death is a precondition of every individual life, but for kinds (species) reproduction presents the opportunity to persist indefinitely.

Behavior

Agency is about agents that act – it is about activity, and in the case of organisms we call that activity behavior. In the human case behavior may be strongly influenced by minded intentions but, since we also speak uninhibitedly about the behavior of molecules, there is no need to treat talk of plant behavior as being unacceptable or metaphorical language.

Behavior is the most direct communicator of agency, and in most cases, it provides the most coherent explanation. Of course, behavior has internal causes but, biologically, these are difficult to access, complex to explain, and more distant in causation. As humans with the ability to describe our own internal states we are accustomed to describing behavior using the language of internal states. We say, for example, ‘She behaved like that because she was jealous‘.

However, while internal conditions initiating behavior are scientifically both fascinating and important, when we provide explanations of events in the world – in say, the course of evolution, it is usually behavior that takes precedence.

Perspective & value

The autonomous agency of organisms is a behavioral orientation that imparts to organisms a ‘perspective’ on the world. This is why organisms are agents and not just passive matter. 

A behavioral orientation towards some goals, rather than others, means that organisms display a kind of mindless normativity: they express pre-conscious ‘preferences’ and ‘choices’. The goals of the biological axiom are not conscious or intentional goals, but they are, nevertheless, goals that may be facilitated or impeded (‘helped’ or ‘hindered’) by circumstance (see the article on biological values for a discussion on the relationship between biological and human values).

The ‘behavior’ of unconscious organisms operates mindlessly by increasing the probabilities of some outcomes over others, notably those that favor their own existence and perpetuation – outcomes that, in human terms, we would describe as ‘beneficial’.

This filtration or ‘favoring’ of some outcomes over others, and the way organisms exhibit ‘preferences’ for one situation over another are what distinguishes the animate from the inanimate.

This propensity for agential behaviour, founded ultimately on the biological axiom (which expresses value through ‘beneficial’ activity) is what makes organisms goal-directed or purposeful.

Adaptation

For simplicity, the adjustments made by organisms conducing to the biological axiom are referred to biologically as adaptations. They are what, in human terms, we might describe as ‘self-correction’ according to circumstance.

In the short-term (one lifetime of fertilization, growth, development, maturation, reproduction, senescence, and death) organisms tend to employ adaptive behaviors that minimize the constraints on their ultimate goals.

Over the long-term (multiple generations), short-term adaptation, by the process of natural selection, results in genetic variation and species-specific evolutionary change to the existing adaptive design.

Kinds of agency

The physical manifestation of agency depends on the unique structures, processes, and behaviors (subsequently contracted to spb) possessed by the organism. While the ultimate goals are the same for all organisms, they are expressed very differently in, say, an amoeba, dandelion, herring, and human. Myriad configurations of structures, processes, and behaviors have evolved to, as it were, comply with the demands of the biological axiom. 

These agential, purposive, and normative properties of organisms (arising out of the agential perspective) preceded people in evolutionary time and they existed in nature mindlessly. That is, the notions of ‘purpose’, ‘value’, and ‘agency’, so strongly associated with human minds, had precursors in mind-independent conditions.

The principles of biological agency (biological axiom) are universal, but the way they are physically manifest in nature by degree.

Large-brained humans are indeed supreme agents. Armed with self-aware hindsight (memory), foresight (anticipation), a ready capacity to learn, accumulate knowledge, and communicate directly using language have resulted in an unprecedented sociality within the animal kingdom. Motivated by elaborate beliefs and desires (ultimately grounded in the biological axiom), we are in a constant process of more or less rational adaptation. This is our paradigm of agential behaviour.

What we ignore is that mindless organisms were the evolutionary precursors to human subjectivity. They express, albeit mindlessly and in crude form, many of the features we associate with human agency. Among these pre-conscious agential characteristics are forms of reasoning, foresight, memory and hindsight, learning, valuation, purpose, intention, and sensation, all expressed through functional (purposive) design and behaviour.

All organisms, through their flexible agency, have the potential for ‘self-correction’ (adaptation) – both short-term and long-term.  in the immediate present and over many generations.

Plant agency

The discussion of agency (above) explained how plants share with all other organisms the ultimate goals of the biological axiom, but that each species expresses agency through its own unique structures, processes, and behaviors.

The question to be addressed in this article asks how plant agency differs from the agency of other organisms.^[3]

Agency (like other factors such as consciousness, values, and knowledge) are treated by this web site as being real properties that, as a consequence of evolution, exist in organisms by degree.

There are many agential characteristics of plants that are shared with other organisms, most notably the goals of the biological axiom itself. What is uniquely different is the mode of expression of this agency.

The following is a list of some of those major physical features that distinguish plants from other organisms:

. plants are either photosynthetic or autotrophic organisms capable of synthesizing their own food, using the pigment chlorophyll to capture the energy of sunlight then used to convert carbon dioxide and water into glucose and oxygen

. plants have rigid cellulose cell walls that provide structural support and protection to 

. plants lack relative mobility, being unable to move, as individuals, from one location to another

. plants display an ‘Alternation of Generations’ as a life cycle moving between a haploid (gametophyte) and diploid (sporophyte) phase leading to the formation of a new generation

. plants have diverse reproductive strategies ranging from sexual through the production of flowers, to asexual e.g. vegetative propagation

. as first colonizers of land, plants are adapted to this environment with roots, stems, and leaves, which facilitate water absorption, structural support, and photosynthesis

. plants form symbiotic relationships such as mutualistic mycorrhizal associations between plant roots and certain fungi, which benefit both plant and fungus

Plant agency, like all biological agency, is expressed through the structures, processes, and behaviors of autonomous organisms whose activity is unified in the objective, universal, and ultimate behavioral propensity to survive, reproduce and flourish. This goal-directed behaviour is most effectively understood and explained from an evolutionary perspective, as a study of comparative agency, with emphasis on those aspects of biological agency that are unique to plants. 

Features of plant agency

From an agential perspective it is significant that the evolutionary challenges of motility seemed, on the one hand, to produce animal nervous systems under the integrated control of brains while plants, instead, use chemical signaling that allow them to respond to environmental cues and coordinate growth and development.

Sensory system

We are accustomed to the idea of nervous systems accessing and distributing internal and external information around the body, this messaging coordinated by a central nervous system.

The complexity and sophistication of nervous systems is attributed to the high demand for information processing that is a consequence of motility. 

Even so, plants also interact with their internal and external conditions using complex systems of communication – electrical, chemical, physiological, and so on. These are all discussed in the article on plant sense.

Motility

Motility confronts the organism with the constant demand for adaptation to changing circumstances.

Individual plants seem impotently static, only achieving distribution of their kind through the dispersal of propagules. This is, in part, a consequence of human temporal perception. Seen through the temporal lens of time-lapse photography the plants on a forest floor do not walk or run, but they are clearly engaged in a fight for life-sustaining light. Climbing plants are exploring surroundings for potential support.

Adaptation

The mindless ‘strategies’ adopted by plants in the ‘struggle for existence’ (title of a chapter in Darwin’s On the origin . . . and characterization of the behavioral motivation to survive, reproduce, and flourish) are truly amazing, even to the sophisticated human mind.

It is recommended that the reader watch the David Attenborough BBC documentary ‘Kingdom of Plants’ to marvel at the mindless but purposeful ‘arms race’ of adaptations to resist herbivores; the grooming of pollinators and seed distributors using color, scent, and flavor; flowers of a single species of orchid that mimic the scent and appearance of a single species of female insect thus luring males of that species into the trap of pollination; the adoption of a carnivorous diet in habitats with nutrient deficiency . . . and so on. The mindless ‘cunning’ of plants is breathtaking.

The fact that these are mindless strategies does not mean that they are not strategies but that we do not have the appropriate non-human agential language to describe them (see the articles human-talk, and being like-minded).

Consciousness

We accept that consciousness can exist by degree: that dogs, fish, and even worms have consciousness, albeit consciousness that is different from human consciousness. We could use specialist terms to distinguish between worm-consciousness, fish-consciousness, and dog-consciousnesses but, instead, we accept that the word ‘consciousness’ can have a semantic breadth that includes animals other than humans while, at the same time, using human consciousness as a reference point (partly because we don’t know what any other kind of consciousness would be like, even though we assume it must be quite different from ours). In other words, we recognize a real (in the world) connection between these different kinds of consciousness: they are variations of the same entity.

Today we understand this connection, not as some vague resemblance, but as part of an evolutionary continuity.

If we assume that worm consciousness is the same as human consciousness, then we are not only being anthropomorphic; we are also, we must assume, in error. But being anthropomorphic (using metaphorical ‘as if’ language) does not mean there is no consciousness in other organisms. All it means is that their consciousness is different from ours.

Brains give us the biologically unique capacity for reason, abstract thought, hindsight and foresight, learning, memory, and language. Plants have none of this. They are brainless, and therefore mindless, and unconscious. This is a vast gulf of difference.

Or is it?

In the following discussion I hope to show how, in the absence of brains and nervous systems, plants still perform many functions that we treat as uniquely brain-related . . . and to an extraordinary degree of sophistication.

Brains do not make as much difference as you might, at first, imagine.

Evolution of consciousness

Humans were created by nature: they are a consequence of natural reasons, natural function, natural value, natural purpose, and natural design. Nature has real (not added by the human mind) mindless reasons, purpose, and design. We resist this idea because we have a top-down human-conscious perspective on the workings of the world and its metaphysics. So, we assume that it is humans who reason, have purposes, and create designs. We forget that just as evolution of matter diversified into a tree of structural variety and graded complexity so its possibilities evolved in a similar way. Reasons, purposes, and design in nature was not created by humans, it ‘Bubbled up from the bottom, not trickled down from the top‘ (Dan Dennett).

Non-conscious reasons and purpose can be regarded as evolutionary precursors to the conscious intention of the mind, and to reason itself, all part of the continuity of goal-directedness inherent in the living world – from the simplest pre-conscious organisms to sentient animals, and rational humans. Teleology did not suddenly arrive on earth with the human intellect. Simply stating what structures and processes ‘do’ does not capture the goal-directed or teleological nature of natural-selection-produced functional adaptations. Aristotle was aware of all this but science is only now coming to grips with this subtle but far-reaching aspect of the world. Antipathy to Aristotle’s natural teleology (the presence within nature itself of ‘ends’ or ‘goals’) was an over-reaction against supernatural and superstitious accounts of nature that were being resisted during the Scientific Revolution. Subsequent philosophical attempts to expurgate teleology from biological language by converting ‘what it is for’ language into the language of ‘what it does’ or ‘how it works’ does not capture the ‘what it is for’ of pre-conscious adaptive selection.

The fact that the human brain was created by an ignorant mechanical process increases the wonder; it produced the intricately designed structural and functional complexity needed to produce reason, language, and abstract thought. As Aristotle noted: organisms like plants do not know, see, or feel with the same teleological intentionality as humans, but they possess a natural teleology. The denial of these reasons, purpose, and design is a human arrogance: it was natural teleology that created both humans and their minds.

Our scientific metaphysics tells us that reasons and purpose in nature are real. Our language will therefore be more effective when brought into line with our best science. It is OK to use quasi-conscious words like ‘design’, ‘purpose’, and ‘function’ because they reflect the quasi-conscious underlying phenomena.

Nature is part of what we might regard as a continuum passing from inanimate simplicity to intentional complexity with all living creatures products of the natural selection that generates functional adaptations. Plants are not conscious so the use of strong consciousness-talk to explain their physiology is metaphor, a distinction that is critical for scientific explanation. We use metaphor when we say that plants can ‘smell’ without a nose and ‘taste’ without a tongue, that they even have ‘awareness’ and ‘knowledge’ of the world as a rudimentary ‘consciousness’. This kind of language may assist our thinking but it also confuses difference.

Of course we can mistakenly attribute human motives to nature. But we must beware of throwing the baby out with the bath water. Nature demonstrates reasons, purposes, and design . . . even though it is unaware that it is doing so.

 The reasoning human brain with its capacity to represent the world in conscious thought, was ‘created’ by natural selection (the ‘struggle for existence’ that is grounded in the biological axiom) . . . an ignorant process devoid of conscious intention.

Human intelligence itself arose out of an unintelligent mechanism . . .  the 3.5-billion-year descent with modification of replicating matter that had acquired the capacity for heritable variation and, in interaction with the environment, differential reproduction. Consciousness gradually emerged out of the countless adaptive modifications and increasing material complexity generated by natural selection.

Our human pride, our anthropocentrism, does not acknowledge, as Aristotle did, that the purpose of human intention is just an extension of the real (not apparent) natural purpose that is inherent in all nature. Aristotle located purpose within nature. Darwin fine-tuned Aristotle’s conclusions by showing how natural selection provided purposive direction via functional adaptation. Then 20th century genetics demonstrated how like begets like, how in life there can be continuity of structure, function, and purpose.

Awareness

Are plants conscious?

Clearly not in the way that we are conscious, but they are much more ‘conscious’ than our intuition might suggest.

We humans are aware and have an extraordinary ability to introspect but there is no philosophical agreement about the reality of the ‘self’ in self-aware: our inner theatre of selfhood could well be illusory. What is important is that we are aware of ‘something’, experiencing ‘something’. In responding to inner and outer environments it is clear that plants are also ‘aware’.

Biological connection

Science has shown that we no longer need to believe that God created each species of organism and placed it on Earth. Only in the last 150 years have we recognized that everything in the universe emerged from a point source at the Big Bang 13.7 billion years ago, and that the entire community of life arose from a common ancestor about 3.5 billion years ago. This means that all the matter in the universe is connected to a single origin, with its living component united through common heredity.

Do you ‘feel’ a greater affinity for plants than for non-living objects . . . or are plants – for all their beauty and utility – mindless and unconscious organisms that are ultimately as purposeless as rocks?

Our contemporary understanding of the history of the universe, and of life in general, would suggest that we have good reason to feel an affinity for all living things.

So how are we related to plants, in an evolutionary sense?

Multicellular animals evolved a little more than 0.5 billion years ago with the last common ancestor of plants and animals, estimated from molecular clock data, dating back about 1.6 billion years.  Though we may never know for sure, it is likely that our common ancestor was a single-celled organism, and modern data suggests something akin to a protozoan.

We might look starkly different from plants but, having the same ultimate origin, we share genes that control metabolic pathways that are common to all living creatures.

What emerges from this characterization is a continuum of matter whose living component exists in degrees of organic complexity, but all with a common ancestor and a history of radiation and diversification by environmental adaptation.

But what does science tell us about the distinctions we make, on the one hand, between the living and non-living and, on the other, between plants and humans.

What, and how great, are our biological similarities and differences?

Plants as intellectual competitors

There are two major ways in which plants have pre-consciously ‘outwitted’ humans.

Firstly, and most dramatically, plants produce their own life-sustaining energy. That is, they manufacture food by using water from the earth, carbon dioxide from the atmosphere, and light from the Sun while they are simply ‘standing still’ … they are photosynthetic. This is an astounding achievement comparable to the evolution of the brain. Photosynthesis produces the energy currency on which the entire natural economy runs: it is the fuel that powers the global cycle of life. Motile organisms must move around to find their food: they must hunt, because they cannot make it themselves. Their energy can only come, ultimately, from plants which are the world’s primary producers. In other words, much of the historical evolutionary effort expended by animals in developing locomotory and nervous systems was only possible because plants had previously ‘solved’ the energy problem needed for life-support. We only have brains because we did not have the pre-conscious ‘intelligence’ to photosynthesize.

Secondly it is plants that were at the core of the Neolithic Agricultural Revolution. To all intents and purposes we have cereal plants to thank or blame for our domestication, our move from wild nature to cities and civilization – probably the most significant human social transition that was a by-product of our attention to vast areas of land where we carefully tended our food plants.

But for our plant-blindness and anthropocentrism it would be blatantly obvious to engineers, architects, artists, and indeed all of us, that plant structures demonstrates a preconscious ‘intelligence’ and ‘beauty’ and functional adaptation of extreme ‘wisdom’ that far exceeds anything our conscious brains can achieve.

Perhaps by using our reasoning consciousness to study and compare the reality of plants with our own human reality we can learn a few adaptive tricks. After all, our consciousness does allow us to make reality comparisons – which is something that a plant’s ‘awareness’ of the world cannot do … at least, not in the same vivid way.

With all this in mind lets now examine the plant functional analogues of the human senses.

Anticipation

Anticipation is a distinctive and critical feature of human conscious experience. It engages hindsight and foresight as tools for the management of behaviour in the present. It is also strongly associated with the concepts of knowing, learning, and remembering. All of these concepts, we assume, require a brain. Without a brain, the idea of plants ‘knowing’ anything at all seems absurd.

But let’s unpack a little of what we mean by a cluster of related concepts that include ‘knowing’, ‘learning’, ‘remembering’ (hindsight), ‘anticipation’.

Memory

Human memory is the subject of active research. Cognitive scientists distinguish between three kinds:

procedural memory – non-verbal or instinctive adjustment to external factors (riding a bicycle)
semantic memory – the acquisition of concepts (learning a language or mathematics)
episodic memory – the recollection of special events (21^st birthday party or breaking a leg). 

Only procedural memory does not require a brain.

Another classification of memory includes:

sensory memory – which filters input from the senses
short-term memory – which can briefly hold up to seven or so objects, like numbers, in consciousness
long-term memory – which retains memories, sometimes for life
muscle-memory – the unconscious memorization of movements like playing a scale on the piano or tying a shoelace
immune memory – when our immune system remembers past infections

Only immune memory does not require a brain.

It also helps to think of memory as involving three key processes:

encoding – memory formation
storage – retention of information
retrieval – the recollection of information

This is the way we understand memory in computers.

Memory is usually related specifically to brains but, when ‘knowing, learning, and remembering’ are treated as ‘manipulating information’ then non-human organisms might be included. We can then usefully apply the last three categories (encoding, storing, and retrieval) to organisms in general.

Encoding

Before we can have conscious memories, we need organisms and one feature of organisms that we tend to take for granted, and Aristotle did not, was the simple fact that ‘like begets like’. Humans do not give birth to fish.

We now know that the community of life almost certainly had a single beginning – that the entire complexity of life in all its complexity and diversity arose by descent with modification from a common ancestor. Only in the mid- 19th century, with Darwin’s theory of natural selection, did the mechanism for encoding this information become a central problem for biology when it was proposed that species changed, or evolved, over time.

Darwin outlined a mechanism whereby small variations in nature would be ‘selected’ (encoded into the characteristics of a particular organism) as a result of differential reproduction. That is, those variations that benefitted the organism would tend to persist under multiple replication. Beneficial variation was essentially a better ‘fit’ with the environment, improved functioning. Over thousands of generations information about the environment was being encoded in the genetic make of different organisms that gradually changed over time. The precise way thi sgenetic information remained unknownfor another century.

Information storage & retrieval

It was only in the 1950s that the astounding foundational structural simplicity of inheritance came to light when Watson and Crick identified the replicating double helix of DNA (present in the chromosomes found in the nucleus of every living cell) consisting of nucleotides in a particular sequence that pass from generation to generation, in egg and sperm, the coded information, as genes, that trigger the formation of those proteins that uniquely determine the physical structure and developmental processes that we associate with a particular species.

Information encoded in DNA is the plant’s blueprint for the future: here are the instructions that detail the way a new organism will unfold in a developmental process that proceeds from juvenile to mature adult as genes switch protein metabolism on and off to produce the structures by which we recognise one species rather than another.

A good example of plant memory occurs in the Venus’s Flytrap. When a fly first touches a hair an electrical potential passes from cell to cell which concentrates the ions in the cell, taking about 20 seconds to return to normal. If the hair is touched again the action potential is sufficient to trigger the trap to shut. This stops the trap shutting unnecessarily in a process that is vary similar to that which occurs in neurons.

Memory seems crucial to our human exisatence, total absence of memory is the subject of thriller movies and is hard to imagine. Pre-conscious plants have no memory at all and yet they have persisted, so how have they compensated? Like all pre-conscious organisms plants possess a rich arsenal of pre-conscious memory analogues. The important capacity from a biological standpoint is not whether we are ‘aware’ of the past but whether the organism has the capacity to incorporate past events into strategies relevant to the present. We call this process ‘learning’ but from a biological perspective From this perspective, whether we refer to these connections with the past as ‘recollection’, or ‘memory’ becomes incidental.

So how can organisms possibly possess these referencing to past events that we call ‘memory’?

Memory is one of the wonders of the biological world. Our genetic makeup, our genotype, carries information about our entire evolutionary history. Most obviously it passes this information from generation to generation as a blueprint that is unique to each kind of organism. A single generation requires a finely-tuned developmental sequence for structures and processes.

Just as humans have (conscious) reasons for their behaviour so a plant has (unconscious) reasons for developing structures that benefit its short and long-term existence. There are beneficial reasons (purposes) for functional design in nature even though these are not conscious reasons. We should not be ashamed of natural teleology even though consciousness-talk may not be appropriate to describe it.

The single key difference between plants and animals is that animals are motile: they can towards benefial influences in the environment and away from disadvantageous ones. Plants have had to confront weather, predators, and disease directly with no means of escape. We might assume that the wide diversity of sensory input needed to cope with mobility has ultimately given rise to nerve tissue. But plants, too, have evolved complex sensory and regulatory systems.

We believe we behave in certain ways due, on the one hand, to our unconscious impulses and intuitions and, on the other, our conscious deliberations. Consciousness, if we believe it has a physical basis that can be explained scientifically, is in this sense at one with all physical phenomena. Consciousness is thus an epiphenomenon of matter.

Plants, like all living organisms today, are a product of evolution extending back 3.5 billion years. Contained in their genes are the ‘memories’ of past environments since it is the historical response of every organism to its ancient environments that has produced the physical bodies they possess today. This we can speak of as genotypic ‘memory’, the inherited memory of the past. But there is also phenotypic memory, the ‘remembered’ response to the environment in the present. This will be discussed under subsequent headings.

It seems that although we have a virtually infinite store of memories the proteins involved in memory maintenance are few.

Biological axioms

We associate science with the establishment of universal laws and general principles about the natural world. Characterized like this we tend to think of the universal laws of physics. Biology is then the subset of complex (living) matter that exists within all-embracing physics.

It is the universal law-like statements of physics that are so impressive as they approximate the absolute certainties of mathematics, and the dictates of Gods.

Maths is built on axioms – statements that are taken as self-evident, foundational, and uncontroversial. A couple of examples from Euclid’s geometry would be that ‘Things that are equal to the same thing are also equal to one another’ and that ‘All right angles are equal to one-another’. To deny an axiom is to place the whole related enterprise or discipline in question. If we argue that Euclid’s axioms are mistaken then we are, in effect, undermining confidence in the entire enterprise of Euclidian geometry.

We respect the empirical generalizations of science (its principles and laws) for their predictive power. Physical constants, the laws of physics, have the properties of axioms because they resist contrary evidence and cannot be altered substantially without transforming our understanding of theoretical foundations. Physical laws are, as it were, the axioms or foundational principles of physics.

Can there be axioms in biology?

Well, if there are axioms in biology then, as a biology student, I was certainly never taught them. Since biology is restricted to the study of life, then its axioms would, presumably, set out life’s universal conditions.

Perhaps the nearest we get to such foundations today is a list of contentious characteristics said to define what it is to be a living being – characteristics like metabolism, nutrition, growth, and reproduction. Though text books often present such a list, getting agreement from the biological community as a whole as to what should appear on this list, (and its order of priority), is no simple matter, especially as definitions of life are further complicated by artificial intelligence and synthetic life forms. This question is therefore generally avoided or not addressed in a coherent way. The idea of biological axioms is therefore reckoned an unproductive avenue of research.

Aristotle was a specialist in first principles. He wrote the world’s first systematic treatise on logic, Organon, much of which still stands today as the foundation for deductive logic. As stated, the strength of axioms is that thay provide a starting point or foundation – they are a backstop to the tendency for scientific questions to pass into an infinite regress.

Aristotle noted that in order to continue existing, to perpetuate their kind, living beings must reproduce. He summarized this principle by saying that all living creatures ‘partake in the eternal and divine’ indicating that they can replicate their kind (species) indefinitely provided they can survive to reproduce. Today, using different words, we might refer, like Richard Dawkins, to the ‘immortality of our genes’. For Aristotle the intellectual search for the foundation of biology, what it means to be a living being, ended with ‘survival and reproduction’. Any cursory examination of general biology texts reveals this as a general (though often not explicit) assumption. It is a truism about life that cannot be expressed in simpler terms.

You might object to the idea of there being any biological axioms, let alone this particular one. Such an axiom does not have the universality of a physical law, nor does it seem to have the same degree of necessity as physical laws. You might think of other properties that are uniquely biological. However, other suggestions – like, say, growth and metabolism -do appear to be second-order.

Four kinds of matter

From antiquity humans have found it useful to distinguish four kinds of matter:

a) the set of all matter ordered by necessity (‘necessity’ = the laws of physics)

b) the subset of all matter that is living, which consists of semi-autonomous units that are the products of natural selection (genetic information accumulated under the influence of the sorting algorithm of natural selection).

c) the subset of living matter that is conscious (sentient) with the capacity to experience comfort and pain

d) the further subset of conscious living matter that has the capacity for foresight and hindsight, abstract reasoning, self-awareness, creation of complex technology, sociality, and language i.e. human beings.

This categorization is useful understanding apparent disjunctions in the continuity of the universe.

The pulse of plant agency is grounded in biological agency – the propensity of all living organisms to survive, reproduce and flourish. It is this mindless plant agency that sustains all life on Earth.

First published on the internet – 1 March 2019

. . . 2 June 2023 – revision
. . . 5 August 2023 – minor editing

GLOBAL OCEANIC & TERRESTRIAL PHOTOTROPH ABUNDANCE –  Sept 1997 to Aug. 2000.
As an estimate of autotroph biomass, it is only a rough indicator of primary production potential and not an actual estimate of it.
Provided by the SeaWiFS Project, Goddard Space Flight Center and ORBIMAGE.
Courtesy Wikimedia Commons – Accessed 9 September 2021