What is life?

                                                        The Cicada – Thopha saccata – Double Drummer
                                   Photograph: Roger Spencer, Ulladulla, New South Wales, Australia, 2017.

An organism can be defined as a living entity composed of cells that, in combination, can perform metabolism, growth, reproduction, respond to stimuli, and maintain homeostasis. However, situating these characteristics within the notion of biological agency provides a more integrated understanding of what it means to be an organism, because organisms are active participants in their conditions of existence (they are subjects as well as objects, and they are paradigmatic biological agents).

An organism is a special kind of matter in the universe because - although it exchanges energy, materials and information with its surroundings - its autonomy is established by its physical boundary, functionally integrated biological organization, and behavioral orientation. Though its behavior has many proximate (immediate and circumstantial) goals, it shares with other organisms a unified biological agency because its structures, processes, and behavior combine to express a goal-directed unity of purpose – the universal, objective, and ultimate propensity of the whole organism to survive, reproduce, adapt, and evolve (the biological axiom). 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, unification, and limit for all proximate goals. This characteristic most obviously distinguishes every living organism from the inanimate and dead, imbuing it with agency as a unity of purpose that preceded human agency and purpose by billions of years. It is this biological agency, as matter with a unity of purpose, that made evolution possible.

Biological processes are goal-directed and that is why biological explanation presupposes agency and purpose. Biology does not make sense unless we know what its objects of study are ‘for’. This dependency arises because nature mindlessly designed all its objects (including the human brain and human subjectivity) for a purpose. When science ignores biological agency's universal and purposive objectives, life assumes the character of inanimate matter, of purposeless physics and chemistry, and biology becomes a goal-less collection of unrelated facts. It is biological agency that makes life intelligible.

Goal-directed behavior in biology is agential and purposive behavior with natural limits or ends that are causally transparent and without mystery: these goals do not imply the supernatural, they do not read human intention into nature, or demand backward causation. Biological goals are generated by internal (immanent) prioritization processes that guide behavior, imbuing organisms with a behavioral orientation that is the functional equivalent of a perspective, attitude, or point of view (see biological values). 

Organisms, as paradigmatic biological agents, adapt by acting on and responding to their conditions of existence as they access, store, process, prioritize, and communicate information in an act of biological cognition that is the evolutionary functional equivalent to human cognition.

Life can be studied from many perspectives and at many scales: it can be distinguished by many of its necessary and unique chemicals, structures, behaviors, and processes, but it is most obviously identified by its functional organization into organisms as the paradigmatic autonomous goal-directed cognitive biological agents.

All biological structures, processes, and behaviors are ultimately subordinate to the universal, objective, and ultimate goals of individual organisms which are therefore the primary reference points for biological explanation.

The intricate design of organisms, which greatly exceeds human ingenuity, was generated by mindless evolutionary processes of biological agency, biological purpose, and biological cognition that also created the human body, human brain, and human subjectivity, and preceded the purpose of human agency by billions of years. Human agency is a highly evolved, limited, and (partly) conscious form of biological agency and biological cognition.

Aristotle’s telos (purpose) was the end or goal of a thing (the first in explanation but last in causation: first in imagination, last in realization) while his anima (strongly resembling today’s agency) was the life-defining or animating principle that enables an entity to realize its potential and strive towards its purpose. This notion of agency, though denied by the Scientific Revolution, and doubted by Darwin himself, was nevertheless the driving force behind natural selection as the mechanism of evolutionary change. Agency is the strongest candidate in any list of necessary and sufficient conditions for life. 

Human agency and human cognition are highly evolved, limited, and (in part) conscious and functionally equivalent forms of biological agency and biological cognition.

This article is one of a series investigating biological agency and its relationship to human agency. These articles are introduced in the article on biological explanation.  Much of the discussion revolves around the scientific appreciation and accommodation of real (genetically inherited) purposive (teleonomic) goal-directedness (agency) that is a universal feature of life. Human agency is treated as 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.

The suite of articles on this topic include: What is life? - the crucial role of agency in determining purposes, values, and what it is to be alive; Purpose - the history of the notion of purpose (teleology) including eight modes (claimed sources of purpose) in biology ; Biological agency - an investigation 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 organismal behavioral propensities (biological normativity); Evolution of biological agency - the actual evolutionary emergence of human agency out of biological agency; Plant sense and Plant intelligence addressing the rapidly developing research field of pre-cognitive agency in plants.

Describing real but non-cognitive agential biological traits (goal-directed behavior) using the language of human cognition results in cognitive metaphor. This has created profound philosophical and semantic confusion (see human-talk).  Formal scientific recognition of pre-cognitive biological agency is, therefore, a combined philosophical, linguistic, and scientific challenge. Though word meanings cannot be changed at will, in science it is possible to refine categories and concepts to better represent the world.^[73] It is being increasingly acknowledged that human agency is a limited, specialized, and highly evolved form of more general biological agency. However, without a formally developed and descriptive technical terminology, the agential properties of organisms are frequently described using language conventionally restricted to human agency – essentially the language of human cognition and intentional psychology. Thus, the increasing scientific application of words like ‘agency’, ‘purpose’, ‘cognition’, ‘intelligence’, ‘reason’, ‘memory’, 'value', and ‘learning’ across biology is broadening their conventional semantic range to include all organisms, and the treatment of such usage as cognitive metaphor is declining.

Introduction – What is Life?

There is a world-weariness about questions like, ‘What is life?’ – a sense that we only tackle such questions in youthful innocence or deluded old age. Life is complex, and since it can be interpreted in many ways, it is foolhardy to attempt any synopsis: many have tried before, unsuccessfully, so we would do better to focus on more productive and meaningful topics.

However appealing or apt this viewpoint might seem, it is not a scientific option.

Stimulus to address this issue comes not only from the practical needs of origin-of-life research, synthetic biology, and astrobiology but from our undeniable awareness that there are two different kinds of matter in the universe . . . the living and the non-living. Biology begins here, so there is no question that science must address this distinction. More to the point, though, is the quality of our answers and the possibility for progress. Haven’t the major biological discoveries of the last 100 years given us greater insight into life?

A simple introduction to the topic might include some general perspectives on the nature of life:

Mechanism – which views organisms and life as complex machinery to be ultimately understood through the laws of physics, chemistry, and materialism, focusing on biological structures and their functions.

Vitalism – posits aspecial “vital force” or “life force” as a unique quality that cannot be fully explained by physical or chemical processes alone. In modern interpretations it explores the subjective and qualitative aspects of living experience.

Biological essentialism – maintains that there is a set of necessary attributes or characteristics that adequately define life. Biological functions, like metabolism, growth, reproduction, and response to stimuli, create a core definition of what it means to be alive.

Organicism – the view that the interconnectedness between organisms and their environments cannot be understood solely through individual components but must be seen understood in terms of organic wholes including ecological and systemic contexts.

Emergentism – suggests that life arises from complex interactions and relationships within systems. In this view, life cannot be simply reduced to its individual parts, as unique properties arise at higher levels or broader scales of organization (e.g., cells forming tissues, tissues forming organs).

Panpsychism – that consciousness or mental properties are fundamental to all aspects of the universe, including life in a gradation of experience and subjectivity most marked in living organisms.

Posthumanism – explores the relationship between humans, technology, and the non-human world and how this can challenge our understanding of what it means to be alive.

A search through biology textbooks and the internet reveals biological esentialism as the most popular current approach: a compilation or list of irreducible phenomena that are typically found in living beings.

Such lists are not intended to be definitional, or definitive, or to provide a set of necessary and sufficient conditions for something to be alive.

A recent book^[45] published in 2023 lists 15 properties of life as follows: reciprocal interdependencies of organic functions, integrated system functions, autonomy, agency, processing of molecules, processing of information, processing of energy, processes that generate form and shape, time autonomy, sensibility and affectability, subjective experience and consciousness, ability to evolve, growth and development, relationship with the environment, and reproduction and death.

A round-up of life-properties popular on the web includes the following: cellular organization, metabolism, homeostasis, growth and development, reproduction, response to stimuli, adaptation through evolution, and genetic material.

It is these and similar properties that introduce students to the study of biology, collectively defining life and distinguishing living organisms from non-living matter.

A new approach

Explanations used in biological science are grounded in two key ideas – agency and evolution – which are derived, respectively, from Aristotle (384 – 322 BCE), and Charles Darwin (1809 – 1882) – often regarded as the founding fathers of biology. In appropriate historical precedence, we now know that without agency evolution could not occur.

Biology began with the systematic thought of Aristotle and his treatment of organisms as biological agents – functionally organized and goal-directed independent units acting on, and responding to, their surroundings in a behaviorally flexible way. This agency was (mostly) a mindless behavioral propensity of organisms to survive and perpetuate their kind. Across the living world there was a vast array of structures, processes and behaviors available for study, but they all supported individual organisms in the attainment of the same ultimate goals. It was these goals – the propensity to survive, reproduce, and adapt to conditions of existence – that signalled ‘life’, rather than the materials out of which they were made.

This life-defining autonomous agency of organisms – their behavioral orientation towards goals, purposes, or ends – gave biological explanations a distinctive and unique character that was strongly associated with Aristotle and called teleology. Though Aristotle had a wide view of teleology he noted the particular strength of agency and purpose in living systems. He had, it seems, established the domain of biology as distinct from other disciplines. Biology was the study of agency and purpose as demonstrated by the goal-directed behavior of living organisms.

Without this foundation in biological agency – knowing what organisms and their structures, processes, and behaviors were ‘for’- biological explanations become inventories of unrelated facts. Aristotle’s purpose (bioteleology or biological agency)  made sense because it distinguished the living from the inanimate and the dead. Asking what a rock, or the moon, is ‘for’ does not make sense because rocks and the moon have no agency.

Aristotle gave Darwin the agential key that was needed to unlock the theory of evolution – the agency at the heart of the ‘struggle for existence’. Darwin’s theory of natural selection accounted for the temporal and physical continuity of agency through evolution by modification from common ancestors – a process that generated the entire community of life.

Biological explanations may apply at many scales, and they can be addressed from many perspectives according to the wide range of biological academic disciplines (anatomy, physiology, genetics, microbiology, psychology, ecology, endocrinology, immunology, and so on) but always its constituent parts – its structures, processes, and behaviors – only have ultimate meaning in relation to the biological agents that provide their context.

This gives rise to a strange and confusing future-directed explanatory priority that is a feature of agential teleology. Only by starting with the biological agent, as a whole, is it possible to determine the ultimate role and causal relations of its parts. It is the biological agent that is the foundation and reference point for biological description: the agent is explanatorily, but not causally, prior. In physics and chemistry, wholes are efficiently explained in terms of their parts: in biology parts are most efficiently, and ultimately, explained in terms of the agency of the wholes they support.

But where did Aristotelian agency come from: what exactly was it that animated matter, that gave organisms independent relevance?

Aristotle did not believe that this ‘life-force’ was a figment or creation of the human mind; nor was it something supernatural or placed in nature by supernatural means – it was real, and it arose from within matter itself.

It would be 2000 years before Darwin provided humanity with a scientific account of life’s agential secret. Darwin showed how living matter was a special kind of matter that replicated itself with variation that incorporated feedback from its environment, so that it had the propensity to not only reproduce, but to also survive, and flourish (biological axiom). So, it was matter with agential autonomy that, within both single and multiple lifetimes, adapted to its surroundings. None of this was a product of conscious intention – either human or supernatural. It was a mindless and inexorable mechanical process that generated the teeming diversity of the community of life, making possible the emergence of the human body, and the subjectivity of the human brain.

Darwin’s powerful theory of natural selection as the mode of evolutionary change preceded the development of genetics and a physical account of heredity. This was later provided by neo-Darwinism (perhaps now better known as the ‘modern synthesis’), a term first used by German naturalist August Weismann in 1883 who prompted the rediscovery of Gregor Mendel’s laws of inheritance by Erich von Tschermak, Hugo deVries, Carl Correns, and William Bateson around 1900. Weismann promoted the theory of germ cells (the later DNA found in the chromosomes of the cell nucleus) that transmit hereditary information, and somatic cells, which do not. The mechanism of inheritance of characteristics was always contentious with Lamarck arguing the ‘inheritance of acquired characteristics’ (a blacksmith’s son having muscles like his Dad). As late as 1868 Darwin supported the idea of evolution relating to ‘use’ and ‘disuse’. Today’s most articulate exposition of neo-Darwinism is ‘The Selfish Gene’ (1976) of Richard Dawkins, now a seminal work in the discipline of evolutionary biology arguing that genes are the fundamental units of natural selection that drive evolutionary processes . . . ‘humans are DNA’s way of making more DNA’. We assume we are in control of our lives, but it is genes that ‘pull the strings’. Reductionism in physics had bottomed out at fundamental particles, and reductionism in biology had mined as deep as the gene.

It was assumed that there would be a strong correlation between traits and genes, but this failed to eventuate after an intensive period of genomics. It seems we do not have a gene for love, being nasty, or nice, or whatever. Such traits are mostly polygenic and gene-trait association rates are low. Causality and control are now being shifted into other regions of biology such as physiology in the form of systems biology and the analysis of function (see, for example, the work of Denis Noble^[2] and his popular book ‘Music of Life’ (2006).

Aristotelian legacy

Science has failed to produce a definition of life that has found general acceptance within the scientific community.

About 2500 years ago ancient Greek philosopher Aristotle noted a unique feature of living systems: they were goal-directed in a way that inanimate and dead things were not.

The goal-directedness of all organisms, not just humans, is an objective fact.^[41] The orientation of behaviour towards ends or goals Aristotle referred to as telos.^[33] He also noted that biological explanations were constrained by this life-defining characteristic. That is, to be meaningful, biological descriptions of organisms – including their structures, processes, and behaviour – must address the question, What is it for – what is its purpose? ^[38] Without having reasons for these structures, behaviors, and processes, biology becomes a list of unrelated facts. Biologists have no option but to adopt this purposive perspective on their subject – treating all organisms as agents. We understand intuitively that asking, What are hands, eyes, talons, and fins for? makes scientific sense because of life’s agency, while the questions, What are mountains and the moon for? seem incoherent.

Thus, much of biology is about reverse engineering as we describe organisms, not just passively in terms of their material composition (as we would describe a rock or the moon), but in terms of ends, functions, and purposes.

Since the Scientific Revolution, up to the present day, mainstream science and philosophy has regarded Aristotle as mistaken. The purpose that we see in nature is a projection of our own human purpose onto nature. Purpose, it is claimed, is a ‘minded’ concept that has no connection with mindless organisms . . . to say that mindless organisms have purposes is a contradiction in terms. Aristotelian teleology and the notion of biological agency are unfortunate relics from a time when nature and organisms were mistakenly imbued with human-like qualities.

But our understanding of biological agency has gathered significance with the emergence of a completely new scientific worldview during the late 19th and early 20th centuries.

This article revisits the question ‘What is life?’ It then makes a critical investigation of the view, still widely held, that the only genuine agency in nature is human agency – that the agency we attribute to nature is not real agency, but the metaphorical as if projection of human agency and purpose onto mostly mindless, purposeless, and merely agent-like organisms. It is argued that this is an unscientific and anthropocentric elevation of minded conscious intention, and a dismissive downgrading of mindless biological agency. By treating the purpose and agency we see in nature as cognitive metaphor or heuristic we deny the real agential and evolutionarily graded reality of the organisms, structures, processes, and behaviours that unite the community of life.

By denying organisms agency they assume an equivalence with the inanimate world of the dead.

A follow-up article on biological agency describes how a simple biological axiom provides a practical and universal definition of what it is to be a living being. This facilitates a more enlightened and objective scientific evolutionary approach to human agency as just one manifestation of biological agency (albeit one that is minded, highly evolved, and of great human interest).

A further article on human-talk (the attribution of human characteristics to non-human organisms, objects, and ideas) then examines the similarities, differences, and connections between humans and other organisms as represented in humanizing language. A further article extends the idea of biological agency into the notion of mindless biological normativity as the evolutionary precursor to human minded subjectivity.

As always, key claims are presented as principles to reflect on and criticize. The principles in this article are not intended as strict definitions, but as clarifications of key terms and ideas presented in the article.

Matter & form

Every natural agent pursues its goals through the activity of its body, so the material body, as the tangible vehicle of agency can quickly become the focus of scientific attention, ignoring or denying the abstract notions of agency and its goals. It is empirically simpler to describe what an organism is made of than what it does. As Aristotle pointed out, the bodies of organisms, and the material out of which they are composed, are not the key features of agency. Bodies are the means by which agents pursue their goals or ends. The crucial defining properties of biological agents is not their matter but their mission (goal, purpose) and their means of aspiring to this mission.

Life’s basic unit

The entire universe has an evolutionary continuity, connection, and interdependence as everything emanated from a point source at the Big Bang, the community of life evolving by descent with modification from a common ancestor.

Biology attempts to understand and explain life from its most inclusive to least inclusive forms – from the operations of the biosphere and ecosystems to the microbiology that explains the mechanism of inheritance.

Each subdiscipline of biology provides us with a different context and focus. But our scientific inclination to analysis (a proven successful methodology), can lead to the unjustified assumption that parts are somehow prior to, more real, important, fundamental, or grounding, than the wholes of which they are a part.

While scientific investigation can begin anywhere, each discipline can develop a sense of self-sufficiency, its objects of study as major initiators of causal chains, and of uniquely crucial within the vast scheme of biological dependencies.

One major task is to find a consensus on the explanatory categories that ‘carve nature at its joints’.

So, in biology today, priority is often given to the cell or gene. Cells and genes were the gold at the bottom of mines of analytic investigation.

All organisms are composed of one or more cells, so cells are small functional units with structures capable of carrying out the processes necessary for life, such as metabolism, reproduction, and the transmission of genetic information. And the autonomy of cells is demonstrated in their capacity for self-replication and self-regulation (homeostasis).

While genes play a crucial role in heredity and the functioning of cells, they are not capable of independent existence. Their effective operation depends on cellular processes, including other genes, proteins, and cellular structures. The cell, with its complete set of genes and the ability to carry out all essential life processes, is sometimes regarded as the basic unit of life.

Organisms are indeed composed of physics and chemistry: they depend on their genes as regulators of structures and processes, and multicellularity probably arose from unicells by means of natural selection. Also, organisms themselves have dependencies within wider frames – populations of their own species, and the wider environment. But it is the singular autonomy of organisms, their narrow agential ultimate focus on survival, reproduction, and flourishing. It is this organismal agency that is special because the operations of organism parts, such as cells and genes – including metabolism, growth, reproduction, response to stimuli, and adaptation – are subordinate to (serve) these overall goals of the organism as an agential unit. This is what singles out the organism as both an intuitive and natural category within the scheme of life.

Levels of organization

Biology is often perceived and studied in terms of hierarchical levels of organization of increasing inclusiveness and complexity. One example would be the series – genes, cells, tissues, organs, organisms, and populations. With the advancement of biological knowledge, each level has assumed the role of a specialist discipline with its own principles and systems of nomenclature, the objects of study assuming their own role in evolutionary selection. The operational units at each level are often regarded as having their own unique functions (purposes) and forms of agency (e.g. the function of the heart is to pump blood).

We give precedence in science to those categories that most effectively assist explanation and understanding. Three categories have become prominent in our understanding of life – the gene, the cell, and the organism.

All organisms are made up of at least one membrane-bound cell and cell theory treats the cell as the basic structural and functional unit of life because the cell is the smallest unit that can replicate independently, and new cells arise from pre-existing cells.

Within the cell, however, are the genes that most efficiently explain the continuity of biological kinds. The information encoded in replicating genes directs the synthesis of proteins that determine the developmental paths and characteristics of organisms. Genes – their structure and function – are therefore crucial to our understanding of inheritance, evolution, and development.

Are there scientific reasons to prioritize one biological category over others, regarding it as somehow more important or significant –  or is this relative to context, scale, and inclination (if I am a geneticist then it makes sense to regard genes as the key to life)?

While cells demonstrate a high degree of autonomy they are usually aggregated into, and subordinate to, the agential demands and conditions determined by the unified activity of entire organisms – ultimately their propensity to survive, reproduce, and flourish. While this requirement exists at all biological scales, the limiting case occurs at the scale of individual organisms which are therefore the primary agential units of life. Though cells and genes have a degree of individuality and independence of operation, it is organisms that we intuitively regard as the basic units of reproduction, growth, adaptation, and agency; they are the paradigmatic exemplars of life processes and homeostasis as they interact autonomously with their environments.

This claim is, of course, based on the assumption that life is more effectively characterized by what it does – its processes and agency – than what it is made of.

While nature and life present us with continuity and gradation, it is organisms as bounded physical entities that constitute the most obvious units of integrated functional organization: they are biological agents whose structures (including cells and genes), processes, and behaviors are subordinate to the agential goals of the entire organism.

While all ‘levels’ can be regarded as expressing their own individuality by degree, it is the organism that stands out as the most discrete unit of agency and evolutionary selection – clearly demarcated as an ecological element, the organism-environment continuum. The ‘levels’ of biology are therefore best understood as being either sub- or supra-organismal.

It is organisms, as biology’s most discrete but agentially unified collections of cells, that are the operational units of biology.

Contemporary cosmology

Our understanding of the universe – its origin, physical composition, properties, and age – has, over the last 150 years, been totally transformed.

Darwinian legacy

The combination of the publication of Darwin‘s On the Origin . . . (1859), and the replacement of the Steady State Theory of the universe with the Big Bang Theory of its origin in the 1930s overturned the prevailing scientific worldview. Darwin showed how all organisms are biologically related to one another in a community of life, while modern cosmology demonstrated that life was, in turn, composed of the stuff of the universe – that all organisms were reconstituted stardust.

Before Darwin it was assumed that the universe was either a supernatural creation or had existed for all time, and biological species were immutable, each created individually by God. The Steady State theory of the universe and biblical account of God’s Creation, including that of biological species, were static and eternal accounts.

Contemporary science represents the universe as a system of process, change, and evolution.  In its first moments it existed as undifferentiated plasma, while today it contains a multiplicity of complex physical kinds. During cosmic evolution matter increased in complexity in a process of emergence as everything, including space and time, evolved from a point source.  Everything in the universe, though not necessarily graded uniformly from one physical form to another is, nevertheless, cosmically continuous and connected, from the first undifferentiated plasma to human brains as matter that has become aware of itself.

In a chronometric revolution that has taken place over just a few generations we can now locate the history of humanity within scientifically verified cosmic, geological, biological, archaeological, historical, and linguistic timeframes. We can date with unprecedented precision the age of the universe, individual rocks and fossils, along with the divergence of biological lineages, human languages, and archaeological remains.

The origin of the universe dates back 13.7 billion years, our solar system 4.6 billion years, and life 3-4 billion years. In the last 50 years our understanding of human biological and cultural evolution has been vastly refined. The genus Homo evolved from former Australopithecines around 3 to 4.4 million years ago, anatomically modern humans appear around 315,000 BP, and our more complex cognitive capacities around 100,000 years ago or earlier (perhaps a consequence of language development and sociality as core group numbers increased from 15-20 individuals in nomadic hunter-gatherer societies to about 150, then more). Permanent migration of modern humans out of Africa occurred about 80-90,000 BP, followed by dispersal across the world, the development of agriculture around 12,000 BP, and the first cities in about 5000 BP until, in the early 21st century, more of the world’s population lived in cities than in the country, with this proportion steadily growing.

This recently acquired timeline has allowed us to frame human existence within the cosmic and scientific timeline of Big History.

Humans did not suddenly spring into nature as conscious, rational, and biologically supreme rulers of planet Earth. Darwin placed humanity at the tip of one twig – one lineage – of a vast Tree of Life, all the branches connected backwards in time to the first rudimentary ancestors of all life.

With this modern scientific worldview of evolutionary continuity and connection in mind, it is now time to examine more closely what it is that makes life unique.

What is life?

In the 21st century the question What is life? remains unanswered.^[36] Academic disciplines now investigate life from many perspectives and each has its own perspectival definition. Overviews of these different approaches, problems that have arisen in dealing with marginal cases, the philosophical difficulties associated with definitions etc. are described in Encyclopaedia Britannica and The Stanford Encyclopaedia of Philosophy, while Wikipedia offers the definition of life that is favored by NASA as: ‘a self-sustaining chemical system capable of Darwinian evolution‘ or ‘matter that can reproduce itself and evolve as survival dictates‘.

What are the key ideas that most effectively crystallize and communicate what it is we mean by ‘life’?

Biology textbooks have tended to emphasize shared biological features such as movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition. From the microbiological perspective of Nobel Laureate Paul Nurse^[44] the key ingredients of life are cells, genes, the capacity to evolve by natural selection, life as chemistry, and life as information. A living thing is a bounded physical entity – like a chemical, physical and informational machine, but it depends on its surroundings and must be able to evolve by natural selection. While partly independent from its environment it is also connected to it by obtaining food and other resources and an interdependence with other organisms. Cells are the basic functional units of life – the smallest entities that can be described as living – since all living things are either cells or collections of cells. Every cell contains a copy of the organism’s entire complement of genes as the blueprint for organismal development. It is genes that provide the most satisfactory material explanation for self-maintenance (survival), growth, and reproduction as spelled out in the organism’s chemistry (biochemistry), the multiplicity of reactions that construct and decompose the molecules of life – its c. 20 amino acids and the powering energy of ATP. It is chemistry that most effectively explains vital processes like metabolism and respiration through a commonality of genes. Life started just once, with organisms closely genetically related in their biochemical processing. Connecting all these elements there is the storage and flow of information.

Definition

Biology is noted for its imprecision and nowhere is this more obvious than in trying to define precisely what we mean when we speak of ‘life’. In seeking simplicity and precision we look for life’s necessary and sufficient conditions – as all and only those conditions necessary to provide an adequate definition. A physicist can point out that the atoms of gold have 79 protons in their nuclei, but life seems to defy such simplicity.

Many conditions may be considered necessary for life. These are often listed in textbooks introducing students to biology, and they are presented as our best attempt to answer the basic question ‘What is life?’

Attempting a succinct contemporary definition of life might seem foolhardy, given its historical difficulty (see e.g. Godfrey-Smith quote at head of page). On the other hand, a clear definition of life would enhance understanding and communication, facilitate education, guide research, and enrich philosophical inquiry. Can biology look beyond its current list of life features to a circumscription of its subject-matter that incorporates the latest biological research and thinking?

Despite the perennial biological difficulties of gradation and exception, the single major hurdle to a consensus definition of life derives from the problem of perspective.

First, there is the perspective of scale. So, for example, humans can be explained using the principles and language related to their physical constituents as chemicals, cells, tissues, organs, and so on – either separately or in combination. Each scale (level) has its own set of principles, concepts, and categories so our choice of explanatory scale(s) depends on the kinds of questions we are posing and the answers we expect. A doctor might be interested in your anatomy if you have broken bones, or your chemistry if you have indigestion. In biology, type scales (levels), are not different things but different ways of describing the same thing. The choice of scale that we use when providing an explanation is therefore a matter of convenience, pragmatism, utility, or context. Historically, biology has been concerned with structures in space from those of large-scale morphology to those of small-scale molecules and genetics. More recently preoccupation with spatial objects has taken account of their temporal dimension through the consideration of the dynamic processes of physiology, developmental biology, behavior, cognition, agency, and evolution.

Can biology provide an account of spatiotemporal scale because, if there are no compelling empirical reasons for prioritizing a particular scale then, it appears, life can be defined using the categories and concepts of any scale (level). This describes today’s biological pluralism with each subject (level, scale) pointing out the necessary significance of its contribution and therefore the dependencies of other subjects.

20^th century research interests focused on physiology, genetics, developmental biology, evolutionary biology, and microbiology, with attention diverted from the whole organism. But, once again, in the 21^st century we see a return to the organism as reference point for biological explanation (in key domains of classification, ecology, and evolution) and therefore in priority of scale. Life is supremely exemplified by organisms with integrated and goal-directed functional organization most aptly characterized as their biological agency. While parts of organisms – their structures (e.g. cells, genes), processes (e.g. metabolism, growth, homeostasis), and behaviors (e.g. response to stimuli, seeking or producing food energy, communication) – often demonstrate a high degree of independence, self-maintenance, and goal-directed functionality, but they are ultimately subordinate to the overarching goals of the entire living organism. Emphasis on reductive molecular-genetic and other explanatory ‘levels’ derives from misplaced hierarchical thinking (see biological hierarchy).

Second, since we must prioritize, we do so by applying rank-value to factors other than scale (see hierarchical thinking in biological hierarchy). Life, we might claim, is best characterized by, say, its functions, principles, behaviors, energy utilization, etc.

But with the most compelling empirical evidence pointing to organisms and their agency as most effectively demonstrating what we mean by life, we must define more clearly what we mean by agency. To persist, organisms must survive, and to survive they must reproduce and adapt which they do by adopting short-term behavioral adjustments that lead ultimately to long-term genetic change as evolution.

Life can now be defined in contemporary terms through the notion of the organism and its dynamic processual agency as understood through the concepts of survival, reproduction, adaptation, and evolution. An alternative way of explaining life in more detail is as the adaptive  process of biological cognition that drives adaptation – the access, storage, and processing of information needed to survive and reproduce.

It is pointed out that life is mostly based on complex organic chemistry based on carbon atoms and water. The chemistry of life revolves around proteins, nucleic acids (DNA and RNA), lipids, and carbohydrates while water acts as a solvent for biochemical reactions, a medium for inner transport, and temperature regulation. Self-replicating nucleic acids store the genetic information as instructions for the construction and operation of the organism. Energy used by organisms comes mostly from the Sun (for those organisms dependent directly or indirectly on photosynthesis) or organic molecules (for heterotrophic organisms) but is sometimes geothermal or chemical. Life processes include the regulation of internal conditions known as homeostasis, metabolism, growth, and reproduction (both sexual and asexual) but necessary for the survival of the species and geetic transmission. Cells are often listed as fundamental structural and functional units of life, typically enclosed by a membrane and with organelles that provide a degree of self-sufficiency.

Biology is notorious for exceptions to general conditions and the possibility of life beyond Earth presents the possibilities of life elsewhere based on different structures and biochemistry.
Biology is now moving away from reductionist philosophy and the assumption that the small is fundamental and therefore more real – so talk about the basic physical building blocks of life – be they organic molecules in general, genes, cells etc. – is going away.

Thinking has moved, instead, towards the processes being performed by structures.

More than matter

Our reductive scientific inclination to look to matter when trying to crystallize the meaning of ‘life’ was ended by Aristotle who pointed out that to be a living human being must entail more than matter.^[1] We cannot be just the matter out of which we are constructed because our body matter changes frequently over a lifetime. Even an artefact like a ship has parts that can, in principle, all be replaced while the ship retains its identity. So, both an organism and a ship have something in addition to their matter that makes them what they are. And this ‘something’ is more than a particular order, structure, or form – as a shape or configuration.

Every living organism is goal-directed; it has a unity of purpose – to survive, reproduce, and flourish – and its parts function in support of the organism attaining these goals. It is a functionally organized agent with a unity of purpose.^[4] Organisms have a unified purpose while their parts, processes and behaviors give functional support to that overall purpose.^[5]

When we consider a species, its individuals also consist of many different shapes, sizes and material constituents, so what we mean by ‘species’ cannot refer to material composition alone.^[5] Finally, if matter is just ‘stuff’, then we clearly need to say something about its structure or organization if we are to proceed with further explanation, or make additional inferences.

Certainly, in the case of living organisms, identity lies not so much in material constituents, more in the continuity of functional structure. While inanimate objects change over time, the agential behaviour of organisms is more self-evidently matter in process.

After Robert Brown’s discovery of the cell nucleus in 1831 cell theory rapidly progressed in the mid-19th century under the influence of German physiologists Matthias Schlieiden and Theodor Schwann when it was established that all living organisms are made up of cells that are produced from pre-existing cells – that cells are the basic units of both living structures, and of reproduction. Then, in the 1880s, chromosomes were experimentally established as the vectors of heredity.

In the 1930s a resolution to the question ‘what is life?’ seemed an attainable aspiration. Darwin had provided what was, in effect, a unified theory of biology, although his work had always lacked an adequate material account of heredity. In 1942 Julian Huxley coined the expression ‘modern synthesis’ to indicate a broad consensus on this genetic component. Though differing slightly in their interpretations, various eminent biologists such as Mayr, Stebbins, Dobzhansky and others accepted the broad principle of natural selection, working on heritable variation supplied by mutation.

It was eagerly anticipated that by drilling ever deeper into the physicochemical constituents of matter, we might eventually find the biological holy grail, the physical secret of life and morphogenesis that was hidden in the ‘immortality’ of our genes.

In part, this is indeed what happened as, in the 1950s, the macromolecules of chromosomes were revealed as constituting a double helix of nucleotides that was, in effect, a genetic code passed from cell to cell under replication. Biochemists James Watson, Francis Crick, and Rosalind Franklin then deciphered this code. Humanity had discovered how the historical blueprint for every organism, reaching back to its first ancient origins, existed in every one of its cells.

Darwin showed how the life-defining agency of organisms that was described by Aristotle could, by means of natural selection, give rise to the entire community of life. Aristotle had described what life was ‘in principle’, while Darwin had shown what it was ‘in practice’. This whole enterprise was then diverted down the rabbit-hole of heredity which is where we still reside. What is the one thing that connects all living organisms (what is life?) – answer – ‘the same set of nucleotides‘. 

This seemed to be the material explanation for many of life’s mysteries that had been lacking in Darwin’s day. The discovery of the structure of DNA was a breakthrough that provided a compelling material answer to the question of what it was to be a living creature. Chromosomes were matter containing the information needed to create biological structure, function, and behaviour. This was the crucial material account of heredity that had been missing from Darwin’s theory.

From another perspective, physicists had noted that organisms were peculiar energy systems.  By a process of self-organization and self-regulation across its lifetime each organism built and maintained autonomous biological order against the pervasive external forces of disorder (entropy). This capacity of organisms to temporarily resist the entropy of the universe Austrian-Irish physicist Erwin Schrödinger referred to in his 1944 popular-science book What is Life? as ‘negative entropy’ (later contracted to negentropy).^[19]

As biological molecules came into greater scientific focus, reductionism thrived through the new subjects of biochemistry and microbiology and their many applications in biotechnology.

In spite of these major breakthroughs, biologists are still unable to find a consensus on what we mean by ‘life’. The many universal characteristics of living organisms^[12] currently defy crystallization into a neat summary package. Life is too complex, it is assumed.

Key characteristics of life are presented to budding biologists as an ever-expanding shopping list of universal properties unearthed by a proliferation of new fields of research.^[13]  So, the search for a simple all-embracing definition of life continues as new disciplines and interests add their voices to our scientific understanding of what it is to be a living organism.

There is a strong sense in which organisms are chemical hardware that embodies a complex digital and analogue information management system . . .  software whose instructions began at the dawn of life and which can be modified, replicated, and passed on to new generations, potentially ad infinitum.  Could information and the language of codes, signals, and transformations be the key that unlocks the door to life?^[32]

This messiness of biological definition could be overcome if one perspective on life were acknowledged as in some way prior to or grounding the others. But finding such a perspective seems unlikely when multiple representations are divided up on pragmatic grounds, and disciplines hunker down within their academic silos.

Rocks, organisms, humans

How do we distinguish life from the non-life of the inanimate physical world, and how can we explain, in a simple and straightforward way, the difference between humans and other organisms?

Life is not passive as a rock is passive. What makes the matter of living organisms a special kind of matter – very different from the inanimate matter of a rock- is its capacity to respond to its internal and external
conditions in an autonomous, unified, and flexible way. In other words, organisms are (real) agents that are goal-directed and purposeful. We can study this behaviour (its reasons, purposes, goals, values) in a scientific way. And, as we have seen, the behavioral flexibility that we associate with this biological agency is grounded in the temporary, universal, objective, and ultimate biological goals of survival, reproduction, and flourishing (the biological axiom).

The biological axiom does not separate humans from other organisms; it states those features that are shared by both. The proximate and uniquely minded goals of human agency evolved out of, but share, these
universal goals of biological agency.

The biological axiom is simultaneously a foundational statement about biological agency, biological purpose, and biological normativity. It describes not only what all organisms do, but the reasons (goals) that motivate this behaviour, including the human reasoning faculty that critically examines these motivations. Biological ageney is grounded mindlessly (objectively) in these biological values.

Mindedness is not a precondition for agency in living organisms: mindedness is simply one expression of biological agency.

From what perspective?

Finding consensus for a definition of life is difficult because biology is studied and explained using multiple systems of representation (perspectives, academic disciplines, frames of reference, levels of organization, points of view). This is a problem compounded by sophisticated technology that extends our knowledge of biology ever further beyond the scale of our human senses, into the micro- and macro-realms.

Part of the problem is also a clash between old and new scientific paradigms – scientists with differing views about the nature of reality – about what should count as a grounding scientific metaphysics.

There is increasing resistance to the once-favored physical reductionism, popular after the 1930s, which gathered momentum with subsequent research into sub-atomic particles and the advances in molecular biology. This view is starkly expressed by Duke University philosopher Alex Rosenberg who claims that ‘physical facts fix all the facts’ and that physical facts reduce to fundamental material constituents . . .  ‘roughly speaking, fermions are what matter is composed of, while bosons are what fields of force are made of ‘^[25] and therefore ‘What ultimately exist are just fermions and bosons and the physical laws that describe the way these particles, and that of the larger objects made up of them, behave‘.

This reductive paradigm is associated with the idea of the unity of science founded on our analytic understanding of physics and its particulate constituents as comprising the ultimate constituents of reality. I call this perspective ‘smallism‘ because it is motivated by the belief that the best scientific explanations must proceed by analysis. That, only by looking at simple parts (regarded as foundational and fundamental) can we unleash the secrets of more complex wholes.

This view is also often associated with a hierarchical metaphysics in which reality is sliced into ‘levels of organization’ which also serve as ‘levels of causation’. In the early days of this scala naturae (Ladder of Life, Great Chain of Being) it was God in the spirit world that pulled the causal strings of existence in a top-down manner, but the Scientific Revolution and unity of science theory sees causation as flowing from the world’s simplest constituents – like its fundamental particles, and DNA, in a bottom-up process.

A contrary view expressed here (sometimes called aspect theory, perspectivism, or holism), acknowledges that everything biological must be physical, but denies that biological phenomena must reduce to physical phenomena . . .  there is no necessary physical reduction. Explanation can proceed by synthesis as well as analysis. From a holistic perspective, wholes have their own irreducible aggregate novel properties and relations that arise as part of the process of emergence – as properties that are not evident in the parts. This strong emergence maintains that parts may be constrained by the nature of the whole – sometimes referred to as top-down causation, although a more general view is that there is no privileged ‘level’ of causation.

On this view we investigate the world through multiple systems of representation – each system of equal validity – and whose representational efficacy is pragmatically determined. There is no ultimate physical reality that we can articulate: ontology itself is perspectival. Nothing in the physical world is more ‘real’ (fundamental) than anything else: a boson or fermion is no more ‘real’ than an elephant or a daffodil . . . or – for that matter – energy, number, quantum fields, consciousness, or information. There are simply diverse (epistemological) ways of interpreting the world depending on our interests and goals.

This is not a form of intellectual relativity but of interpretation. Each representational system has its own standards and measures of excellence and efficacy, often with its own domain-specific principles, procedures, terminologies, and explanatory goals that are integrated with other systems and capable of endless refinement.

So, in practice, we explain life in terms ranging in scale from global ecology to molecular biology, from physical structures to behaviours, activities, processes, and functions, from informational content to its means of communication . . . and much more.^[13]  It is this multiplicity of representational systems that decreases the likelihood of academic agreement on a definitional cement that can bind all life together.

Aristotle

About 2,500 years ago the Ancient Greek philosopher Aristotle (considered the founder of biological science) outlined four major ways that we use to explain the world, known as his four (be)’causes’. He noted that providing a satisfying explanation often (but not always) required consideration of all four factors, these being: what it is made of, how it originated, its unique features, and what it is for.

A modern example of the application of Aristotle’s four causes might be the way that biologists have argued about the best way to define the gene: should it be structural (material cause), positional (formal cause), historical (efficient cause), or functional (final cause)?

This schema provides a surprisingly neat summary of different approaches to the biological definition of life today.

Aristotle’s biographer Armand Leroi, an evolutionary biologist working at Imperial College, London, presents Aristotle’s causes in a schema that represents today’s biology in a very general way by equating material cause to biochemistry and physiology, formal cause to genetics, efficient cause to developmental biology and neurophysiology, and final cause to evolutionary biology and the study of function and adaptation.^[31] Leroi concludes that Aristotle totally transformed the transcendental world of Plato ‘ . . . by the time he was done, matter, form, purpose and change were no longer the playthings of speculative philosophy but a research program’.

But history has rejected Aristotle’s claim that, when considering life, it is the fourth ’cause’ that must take precedence.  He insisted that in living nature almost everything was directed towards goals – organisms, processes, structures, functions, behaviour and so on . . . all were invariably ‘for’ something in a way that was not so evident in the inanimate world. This goal-directed agency, he observed, arose from within organisms themselves: it was not imposed from outside by, say, a supernatural agency, or the human imagination. It was as though every organism contained an ‘inner craftsman’ designing all aspects of that organism’s life for a (mindless) reason or purpose. ‘Nature does nothing in vain’, he claimed.

Modern science has replied that without the conscious intention of man or God the goal-directedness of nature is not real but, at best, only agent-like – that adaptations only appear to be designed for a purpose.

The Scientific Revolution

Aristotle’s observations on purpose in nature, and his doctrine of final causes lost favour during the Scientific Revolution (c. 1550 to 1750) as a new breed of thinkers questioned ancient authorities – challenging the two sources of what was considered secure knowledge – the Bible and Aristotle’s philosophical ideas. Aristotle’s ideas, especially, were attacked as part of the process of scientific rejuvenation. Old ideas needed to be challenged if science was to move forward and, as scientific knowledge advanced, it was not difficult to demonstrate empirical errors in Aristotle’s thinking. A new emphasis on experiment and observation brought science down to Earth downplaying the relative obscurities of Aristotle’s deductive logic and metaphysics.

Intellectuals of the European Renaissance and Enlightenment (impressive authorities like Bacon (1561-1623), Descartes (1596-1650), Spinoza (1632-1677), Hume (1711-1776), and Kant (1724-1804)) all thought that the purpose Aristotle saw in nature, its teleology, was making the old mistake of imbuing unconscious nature with conscious intentions.

This dismissive view of telos was reinforced by the way that casual anthropomorphic personification and metaphor imbued non-conscious organisms with conscious intentions. Telos was too abstract: it had the ring of a mysterious and unnecessary internal supernatural and non-empirical vitalistic force that was contrary to the newly invigorated and empirically grounded mode of enquiry.

The question remains: is agency a part of the biological world, of life itself, or is it a projection of human minds? If it is real, then where does it come from – how do we explain it? Is this a philosophical problem of no practical biological consequence . . . or maybe only a question of semantics? And how can a phenomenon as abstract as agency provide a meaningful focus for all life when biology is a subject of proliferating perspectives and expanding scales?

The inherited certitude of thinkers of the Scientific Revolution and Enlightenment is now under question. It is possible that, in their enthusiasm to rid science of superstition and human subjectivity, they went too far.

Darwin’s theory of evolution achieved three outcomes whose consequences are yet to be absorbed into the body of biological thought – and all have a bearing on the question of biological agency:

First, in spite of the biological use of metaphorical and anthropomorphic language (referred to here as human-talk), Darwin nevertheless naturalized Aristotle’s telos by demonstrating how natural selection gives rise to goal-directed behaviour and functional adaptations (purposive attributes) in a scientifically accountable and mechanical way. He demonstrated that purpose in nature is ‘real’, it is not confined to human minds.

Second, a finding whose philosophical consequences have not yet been fully realized, he replaced the old idea of discretely created species with a new notion of organic connection and continuity.

Third, he replaced the old mental image of life as a ladder with humans enthroned on the top rung, with the new image of life as a tree and humans at the tip of just one of its many branches.

These three compelling findings are yet to take up residence in the philosophy of biology as part of our scientific metaphysics.

The article on biological agency provides a simple, practical, and common-sense outline of: what it is to be a living being; how human agency is a minded evolutionary extension of biological agency; and why we frequently resort to human-talk (anthropomorphism) when describing non-human organisms.

The algorithm of life

We recognize life most obviously in the form of living organisms as autonomous units of matter that are reactive to the circumstances that exist both inside and outside themselves. Organisms undergo a mechanical process that has the potential to maintain their kind in perpetuity, referred to here as the algorithm of life.

It was Darwin who, in the mid-19th century, gave a scientific explanation of the way this provided physical continuity to the first living organisms that were to become the entire community of life we know today – through a process of descent with modification from a common ancestor.

Life is most evident to us through  physically bounded and autonomous units of matter (organisms) that have a behavioral propensity (agency) to survive, reproduce, and flourish. This they do by adapting to their conditions of existence over both the short- and long-terms. Natural variation subjected to selection over many generations incorporates feedback from the environment,facilitating their agential goals.

Though this is a simple mechanical process operating like a mathematical formula with a feedback loop, the autonomy it gives to organisms is an independence of action that is most economically described as ‘agency’.

The agency expressed by the algorithm of life can be summarized in the more familiar and purposive terms of biological existence as the propensity to survive, reproduce, and flourish (the biological axiom).

A human perspective

In science there can be no privileged perspective on the world. Each biological discipline makes its own particular contribution to our understanding of life, and it does this in its own way. And in all scientific study we try to minimize the influence of our human presence.

Does this mean that we can say nothing definitive about the essential characteristics of life?

Once again, Aristotle comes to the rescue. He, as much as anyone in recorded history, struggled for ‘best explanation’ aided by his toolbox of four ‘(be)causes’:

Material cause  –   what is it made of?
Efficient cause  –   what produced it, how did it come to be?
Formal cause    –   what is its essential defining feature?
Final cause        –   what is its goal; what is it for?

Aristotle’s four causes remain a powerful combination today. They are both static and dynamic, including both past and present, while at the same time incorporating both structure and function.  By considering potentiality, actuality, and the temporal sequence of efficient cause they allow for history, development, purpose, and agency. They explain the way things are now, but also account for change by explaining how they came to be. There is ample consideration of organisms as process. And the meaning of each ‘because’ allows some flexibility of interpretation (Aristotle pointed out that the Greek word aition as ’cause’ had various senses).

Of special significance is the fact that the four causes divide neatly into two pairs that provide explanations using the modes of both analysis and synthesis. The material and efficient causes capture an analytic ‘bottom-up’ physical and material perspective on the world and change, while formal and final causes offer a ‘top-down’ synthetic, integrating, unifying, agential and purposeful perspective.

The Scientific Revolution was dominated by men who were mathematicians and astronomers describing a mechanistic world of matter in motion.^[1] They abandoned formal and final cause, and in so doing they reduced life to the material and efficient causes that explained the inanimate world so well. By restricting purpose and agency to humans, and without the benefit of the theory of evolution, humans had minimal continuity with the community of life. Humans with conscious deliberating minds were set over, above, and apart from all else, bar God.

So, what do these ‘becauses’ look like today, 2500 years after the foundation of biology by Aristotle?

As already pointed out – there is wiggle-room for interpretation here – but the following is an attempt to explain life on Aristotle’s terms:

What is the matter that life is made of? Living matter consists of functionally organized (purposeful and agential) individuals (organisms) described by science at many structural and functional scales

What produced life, how did it come to be? Life originated as matter that is goal-directed – that expresses agency – the entire community of life arising by descent with modification from common ancestry

What is the essential defining feature of life? Life’s shared defining features are communicated between generations as information contained within a genetic code

What is life’s goal – what is it for? The ultimate goal of life is to survive, reproduce, and flourish, while proximate human goals focus more on happiness and wellbeing

These ideas are loosely adapted into the opening paragraph at the head of this article.

Aristotle summarized his work in biology by using an uncharacteristically mystical and poetic phrase. From more than 2000 years ago he passed to us the message that all living things ‘partake in the eternal and divine‘. Darwin would never have made such a statement. We are tempted to smile and allow Aristotle a momentary and moving literary flourish, but this would be a mistake. His scientific investigations began with the examination of change and the paradox of permanence in change. One pillar of his teleology was the observation that though individuals perish, their form persists from generation to generation . . . what today we might call the immortality of our genes. To the Greek mind, and ours, immortality was equated with the divine. The most natural function of living things is to produce others like themselves – and in so doing they are immortal, participating in the eternal and divine. Nothing that is perishable is able to ‘remain the same and one in number’ but through reproduction it ‘remains not the same, but like the same, not one in number but one in form.’ (Anima II, 415a23-b7).

What is still not scientifically acknowledged is that Darwin did not explain Aristotle’s teleology away. He gave nature’s purpose, agency, and design scientific credibility. He re-connected humans to their biologically graded origins.

The agency and purpose that exists in nature, the goal-directed behaviour of all organisms, was present in nature before the advent of human minds. Its intricate design greatly surpasses any human attempts at design.^[39] Nature created human bodies and human brains – and human agency (not vice-versa).

So, if the purpose, agency, and design that is present in nature is not imposed from outside by some intelligent or vital force – and not mapped onto the world in some way by the human mind, then it must have arisen from within nature itself. Species-specific designs are repeated from generation to generation, again and again in a path-dependent way. Design in nature produces functional adaptations that are ‘for the good’ or ‘for the better’ and goals or ends with beneficiaries are acceptably referred to as purposes. None of this entails the supernatural or mind-dependent metaphor. All of this was well known and clearly stated by Aristotle who called it telos . . . but 2000 years would pass before Darwin eventually provided a scientific account of the origin of this intrinsic goal-directedness.

Our confusion arises from what philosopher Dan Dennett has called Darwin’s ‘strange inversion of reasoning‘, our refusal to accept that natural selection is ‘for without foresight‘ producing organic wholes that are ‘competent without comprehension‘ (Dennett) . . . that purpose ‘bubbles up from the bottom, not trickles down from the top‘ (Dennett). Nature created human bodies and human brains – and human agency (not vice-versa). Human arrogance refuses to admit our humble origins.

When Richard Dawkins states that biology is ‘The study of complicated things that give the appearance of being designed for a purpose’^[56] he is making a statement that uncompromisingly links ‘purpose’ to ‘conscious intention’. In doing this he ignores the way teleology is firmly embedded in both biological discourse and nature itself, and he joins those who consider the investigation of purpose and function in biology as a matter of heuristic convenience. In so doing he restricts the word ‘purpose’ to human intention, downplaying the miraculous purposive achievements of natural selection (including ourselves). In a bid to exorcise from biology any hint of the Argument from Design he has thrown the baby out with the bathwater.^[57]

Because we usually encounter design and purpose as a consequence of human planning (which includes hindsight and foresight) this does not mean that purpose in nature cannot be real. Limiting purpose-talk to situations involving human subjectivity renders natural teleology, by definition, a human construct. This article and others on this web site have argued that teleology did not arrive on earth abruptly with the human intellect and that purpose and design in nature are real; they are part of the fabric of the natural world, not a creation of our minds, and that is why attempts to purge biology of purpose-talk have failed. Though consciousness-talk is, on occasion, used as metaphor in biology this does not mean that there is only apparent purpose and design in nature. Design and purpose in nature are not metaphorical but literal.

To remove teleology from biology is not just the harmless elimination of metaphor, it is a reduction that diminishes our biological understanding of what exists in the texture of the world. It places living matter on a similar footing to inanimate matter in the realm of purpose, design, function, and value (making the distinction between human values on the one hand, and facts of science on the other, appear clear-cut), and diminishes the wonder of what natural selection has created.

This is not just a semantic debate about what we mean by the word ‘purpose’; it is a metaphysical argument about what exists in ‘reality’ as our best possible scientific explanation.

It is OK to ascribe purpose and design to nature, to use the word ‘for’ in explaining the purposes of organisms as whole individuals, and the functions of their parts, and to treat organisms as real, not metaphorical, agents.

Biological explanation

Biological explanations, provided from many perspectives and scales, are grounded in biological agency as the behavioral propensity of organisms to survive, reproduce, and flourish (biological axiom). This agency is the objective goal-directedness of organisms as biological agents acting on, and reacting to, their environments.

The organism, as an independent biological agent interacting with its surroundings, is the foundational unit of biology, and it is this autonomy of functional organization of organisms that establishes its distinction from its academic colleagues, mathematics, physics, chemistry, and the description of inanimate matter. It is the strength this organismal autonomy that distinguishes it from looser comparable collectives like genes, cells, and termite colonies.

These foundational features of biology were established by its founding fathers, Aristotle and Darwin. Aristotle observed that the behavior of organisms, as autonomous agents, is directed towards ends (goals) that existed within organisms themselves and were not necessarily placed in nature by God, backward causation, or the human imagination. Without understanding these ends (teleology), biology was a listing of unrelated facts. Darwin provided a temporal account of organic change that explained the origin and diversification of the entire community of life – of how organisms are the products of evolution by descent with modification from common ancestors. Organic change occurs as natural selection which accepts environmental feedback as adaptation to ever-changing environments. Though adaptation exists at many scales these are all ultimately subordinate to the organismal scale.

Biological agency provides the ultimate explanation for biological activity at all scales. Each biological discipline provides biological explanations of structures and functions. But whether it be the study of genes, DNA, hormones, immunity, the intricate interplay of biochemicals and cells, the transmission of chemical signals . . . the description of processes like photosynthesis, metabolism, respiration, reproduction, and development . . . or the role of organisms in populations and ecosystems. Only by recognizing the ultimate role of biological agency do biological structures, processes, and behaviors make sense. It is biological agency that unifies biology as a discipline. Biology without Aristotle’s ‘ends’ is indistinguishable from studies of the inanimate and dead.

Aristotle’s philosophy acknowledged that an account of the world must have not only a static description of matter, it must also include the dynamism of motion, process, and change. Living things, especially, displayed capacities, possibilities or powers for change as potentialities for actualization as a (temporary) limit, end, or full realization. Potentiality provides the capacity for change and development, while actuality represents the fulfillment of that potential. He argued that actuality is not merely the end result but is an ongoing process of realizing the potential that exists within something.

Importantly, Aristotle pointed out that, in explanation, actuality is prior to potentiality. For something to have the potential to become something else, there must already be an actualized entity or state from which it derives its potential. This relationship between potentiality and actuality reflects Aristotle’s belief in the teleological order of nature in which processes have an inner propensity to direct change (potentiality) towards ends (actuality). So, for example, the potential of an acorn is realized in its actualization as a mature oak tree.

The importance of explanatory priority and teleology to biology needs underlining.

Principle biological explanations are grounded in two key ideas: the agential goal-directedness of autonomous organisms (the biological agency of Aristotelian teleology), and the temporal physical continuity of the community of life due to its origin by natural selection from a common ancestor (Darwinian evolution).

Explanatory priority

To make sense of the world we intuitively fragment it into wholes and their parts – parts of physical objects, processes, and ideas. Before we understand the significance of parts, we must first have a conception of the whole. The notion of a part presupposes a whole. A leg has meaning in relation to a body, a brick in relation to a house. The body and house have explanatory priority because without understanding their place in the whole, their significance as parts is lost – the leg and brick lack contextual meaning. At face value this seems straightforward, but it has great potential for confusion, partly because it is taken for granted, and its significance therefore lost, but also because parts can themselves take on the conceptual role of wholes. Our focus of interest in a leg might lie in its anatomy, rather than its ultimate role in the agency of the organism of which it is a part.

The significance of biological agency is that it provides an ultimate explanation when, for the most part, proximate explanations provide the answers we require. When studying the structure and function of genes the overall agency of the organisms in which they are found is of minor concern.

However, biological structures, processes, and behaviors only make ultimate sense in terms of the autonomous agency of whole organisms. The autonomous agency of the organism is paramount. Organisms can, of course, become parts of greater wholes – but the integrity and strength of their autonomy and individuality is special in biology. The significance of agency in biology hardly features in biological theory and so biological explanations tend to either ignore it altogether, or to find the explanation of parts sufficient for purpose.

Ends

Much of the confusion with teleology and ends relates to explanatory priority. If we begin with an understanding of a house and then explain it in terms of its component parts, then it seems as though the house is causing the parts – that there is backward causation. If I study to pass an examination it seems as though an event in the future is causing my behavior. But, of course, the house was built up from its parts, it is only in explanation, in understanding, that the whole precedes the parts. It is my anticipation in the present not an event in the future that makes me study.

Even when explanatory priority is accepted it is then a small step to the conclusion that there are no ends, that the concept of the house or examination as ‘ends’ is something that is not in the world but creations of our minds, some kind of imaginary fiction, or philosophical abstraction. But ends in biology need not be supernatural or psychological, they are mostly real. The ends of the biological axiom are an objective part of the fabric of the universe – a consequence of causal processes that are open to empirical experiment and observation. There is no attached mystery, obfuscation, supernatural force or power, creative imagination, heuristics, linguistic playfulness, or philosophical smoke and mirrors. Biological ends are biological facts.

Toronto Professor of philosophy Denis Walsh summarizes the situation as follows:

The ‘Aristotelian purge’ was seen as a pivotal achievement of early modern science. As a consequence of the scientific revolution, the natural sciences learned to live without teleology. Current evolutionary biology, I contend, demonstrates that quite the opposite lesson needs now to be learned. The understanding of how evolution can be adaptive requires us to incorporate teleology – issuing from the goal-directed, adaptive plasticity of organisms –as a legitimate scientific form of explanation. The natural sciences must, once again, learn to live with teleology.^[3]

Re-definition

What is it that distinguishes the living from the inanimate and the dead? Isn’t biology just complicated mathematics, physics, or chemistry – after all, organisms are just physicochemical processes . . . aren’t they?

It seems that we have given up on trying to provide a succinct definition of life. This is a problem that has been placed in the ‘too hard’ basket and, instead, we have fallen back on a long list of ‘family resemblance’ characteristics with the observation that biology is notorious for its grey areas, gradations, and exceptions to the rule.

For a while it seemed that science would find answers to questions about physical reality by drilling down to the smallest possible ingredients – the fundamental particles of physics, and the genes of biology. But being small does not make you more real. Parts help to explain wholes, but wholes have their own reality. 

It was Aristotle who observed that organisms were not passive; they were different from rocks and planets because they were active agents: their behavior was directed towards specific goals or ends in the same way that humans intentionally pursued goals.

Biologists have withdrawn into their academic silos, defining life in the technical terms associated with their biological subdisciplines (genetics, physiology, anatomy, etc.). So, we now perceive life as viewed from many scales and perspectives.

However, the structures, processes, and behaviors that constitute the substance of biological science lack meaning and coherence unless ultimately considered in relation to the agency of autonomous organisms.

Biology is an indefinite science with gradations, exceptions, and imprecise distinctions. The boundary between life and non-life is a long-disputed territory populated by viruses, extremophiles, hi-tec simulations, and more. But two features stand out.

First, the operation of organisms as independent and autonomous agents as they act on, and respond to, their surroundings with flexible behavior that is orientated towards survival, reproduction, and flourishing.  This behavioral orientation is not intentional – it is not a minded orientation – but it gives all life a similar ‘direction’ that, in human minded terms, could be described as a ‘perspective’, or ‘point of view’. It is this agential and forward-looking directionality present in all living organisms that is suggested in Aristotle’s teleology.

Second, Aristotle did not give a physical account of how agency arises and persists in organisms, so his entelechy (the internal principle which actualizes potential) was rejected by the Scientific Revolution as a philosophically obscure, mysterious, and supernatural vital force. But Darwin’s theory of natural selection provided a naturalistic and compelling account of the origin of the entire community of life, and it did not invoke the supernatural, human creative imagination, or backward causation.

Aristotle and Darwin, when considered together, provide us with a more than adequate foundational scientific account of life.

There are many processes, structures, and behaviors that are found only in living organisms.  There is growth, metabolism, respiration, the miracle of DNA replication and protein generation as traits encoded in genes, of long-term adaptation, the interaction of organisms with their environments, and in an age of intense microbiological technology it seems we can describe much of biology in reductive physicochemical terms.

But all of this is subordinate to the agential unity of purpose expressed by each individual organism – the universal behavioral propensity of living organisms to survive, reproduce, and flourish. Only under the ultimate conditions of biological agency do biological structures, processes, and behaviors make sense.

‘Life is distinguished by the agency manifest in autonomous units of matter (organisms) which, unlike inanimate matter, have the capacity to act on, and respond to, their environments with flexible behavior that is orientated towards survival, reproduction, and flourishing.
Living systems are information processors with a behavioral orientation that includes the capacity to adapt according to Darwinian principles. Human agency is a highly evolved and minded form of biological agency.’

PlantsPeoplePlanet – September 2023

These characteristics are what most obviously distinguish every organism from inanimate objects and the dead. Without an acknowledgment of the universal and purposive goals of biological agency, life assumes the character of inanimate matter, of purposeless physics and chemistry, while biology itself becomes a collection of unrelated facts.

‘

Summary

In answering the question ‘What is life?’, the answer we give may depend on our perspective, say, evolutionary, physiological, genetic . . . Or perhaps it depends on the scale of our interest, which nowadays might range from molecules to ecosystems. Aristotle observed that there are four major kinds of explanation of something, his four (be)causes: how it is structured, what it is made of, how it originated, or what it was for.

On what grounds do we prioritize these factors or, indeed, make any selection?

Agential biologists point out that life emerged from inanimate matter when its agential preconditions arose for the first time in nature, and that natural selection and gene frequencies are by-products of this biological agency.

Biologist Richard Dawkins regards ‘functional complexity’ as diagnostic of life.^[29]

When comparing the animate to the inanimate it is immediately apparent that organisms manifest a unified and purposeful autonomy that is not present in a rock or a dead body. Metabolic processes are themselves sufficient to distinguish a living organism from a rock.

But, more than this: life has a scientifically investigable order that is different from the scientific order we investigate in inanimate matter; this uniquely biological order is the mindless emergent agency that connects to our own specialist human minded agency.

It is biological agency, as matter that expresses goals (ends or purposes), that provides the best explanation of Darwin’s ‘struggle for existence’ and for life itself. It was Aristotle, not Darwin, who laid the foundations for biological science, a conclusion that has taken us over 2000 years to rediscover.

In an attempt to succinctly express, as nearly as possible, the necessary and sufficient conditions for life, biologists have produced a list of shared necessary characteristics, acknowledging that there are exceptions and variations. Popular among these characteristics are: cellular organization, metabolism, homeostasis, growth, adaptation, response to stimuli, and reproduction.

PPP maintains that it is the agential aggregation into functional units of organization, as organisms, that most aptly captures the nature of life. What, then, are the properties that uniquely describe these behavioral units – the necessary and sufficient conditions for their existence?

It is their minimal capacity to survive and reproduce with flexible behavior that adapts to its conditions of existence. It is the specific means of adaptation that distinguishes living organisms from, say, computer-generated or other entities fulfilling these criteria.

If the evolution of the community of life arose as a consequence of (a by-product of) these agential goals, as claimed here and elsewhere, then they warrant biological recognition, proposed here as a biological axiom.

Glossary - Biological Agency

Adaptation (biological) – the word 'adaptation' expresses, in the most parsimonious way, the means by which organisms, as biological agents, attain their goals. 'Adaptation' can refer to a structure, process, or behavior (a trait). The process by which populations of organisms change over many generations in response to environmental factors, developing heritable traits that enhance their survival and reproductive success in specific environments; the evolution of traits with functions that enhance fitness (being conducive to survival, reproduction, and flourishing); the capacity for self-correction - in the short-term through behavioral flexibility, leading to long-term genetic change
Agency - (general) the capacity to act on and react to conditions of existence with goal-directed behavior; (biological) the mostly mindless autonomous capacity of biological individuals to act on, and react to, their conditions of existence (both internal and external) in a unified, goal-directed but flexible way (see biological axiom). Agency is the physical manifestation of functionally integrated behavior. Human agency is biological agency supplemented by the evolved resources of the human mind including: language, self-reflective and conscious reason, hindsight, foresight, and abstract thought
Agent - something that acts or brings things about. Mindless inorganic agents include objects like missiles, cities, and computers. In biology - an organism as autonomous matter with the capacity to behave in a unified goal-directed way as stated by the biological axiom (sometimes extended to include genes, groups, or other entities, even natural selection itself) as a (semi)autonomous individual with inputs as flows of energy, materials, and information, internal processing, and outputs as energy, waste, action and reaction in relation to inner and outer environments. An organism motivated by real goals (these may be mindless, that is, without conscious intention);  an agent can act and react; it is the instrument or means by which a purpose is pursued
Agential realism - the claim that non-human organisms exhibit agency in a mindless way, and that humans combine both mindless and minded agency: the grounding of cognitive biological metaphors in non-cognitive biological facts
Algorithm of life - life is autonomous and agential matter that self-replicates with variation that, by a process of evolutionary selection, incorporates feedback from the environment thus facilitating its persistence.

1. Endow units of matter with agency as the capacity to adapt to their conditions of existence (to survive, reproduce, and flourish).
2. Combine the behavioral orientation of 1 with genetic modifications arising in each new generation
3. Expose 2 to evolutionary selection pressures resulting in differential survival
4. Surviving forms return to step 2

Anthropocentric - to view and interpret circumstances in terms of human experience and values
Anthropomorphism - the attribution of human traits, emotions, or intentions to non-human entities
Apomorphy - a specialized trait or character that is unique to a group or species: a character state (such as the presence of feathers) that is not present in an ancestral form
Autopoiesis - self-replication combined with self-maintenance and modification is sometimes referred to as autopoiesis
Behavior (biology) - the outward expression of the internal processes of biological cognition; actions performed by a biological agent (or, more loosely, its parts); the internally coordinated but externally observable response of whole organisms to internal and external stimuli. Behaviour may be: mindless or minded; conscious, unconscious, or subconscious; overt or covert; innate or learned; voluntary or involuntary. Learning capacity is graded in complexity
Behavioral ecology – the study of the evolution of animal behavior in response to environmental pressures
Biological agency - the capacity of autonomous living organisms as biological agents to act on, and respond to, their conditions of existence in a flexible way and with a unity of adaptive purpose - the goal-directed behavioral propensity to survive, reproduce, and flourish; the capacity of living organisms to act with intentionality; a life-defining property of living organisms; the motivation for biological activity as described by the biological axiom; the capacity of organisms to act with purpose and intentionality; the biological principle that has generated the entire community of life; the capacity organisms act intentionally in the sense that their behavior is purposeful and adaptive i.e. directed towards objects, properties, or states of affairs
Biological agent - while biological agency, in a broad sense. can be ascribed to almost any biological structure, process, or behavior, it is the organism that best serves as its exemplar, standard, or prototype cf. organism, biological agency. an organism as an autonomous unit of matter with a flexible and adaptive propensity to survive, reproduce, and flourish (the universal, objective, and ultimate unity of purpose shared by all life); biological agents, organisms are self-replicating units that regulate the internal and external exchange of energy, materials, and information that is required for their autonomous pursuit of goals
Biological axiom – a universal biological principle paradigmatically exemplified by living organisms as biological agents that express their autonomy in a unity of adaptive purpose – the universal, objective, and ultimate behavioral propensity to survive, reproduce, and flourish in the face of their conditions of existence (sometimes referred to in evolutionary biology as 'fitness maximization'). These goals may be met in both cognitive and non-cognitive ways: they are universal because these are characteristics demonstrated by all organisms, objective because they are a mind-independent fact, and ultimate because they are a summation of all proximate goals. While aberrations may be found, the biological axiom is a processual and agential definition that expresses with greater clarity than definitions describing structures, the necessary and sufficient ancestral agential characteristics that define all life. cf. organism, biological agent.
Biological cognition - the accession, storage, interpretation, and processing of information necessary for biological agents to adapt to their conditions of existence. In its highly evolved sentient form, this entails the mental processes of perceiving, interpreting, and responding to stimuli that encompasses learning, memory, problem-solving, and decision-making, all grounded in the brain's structure and function as shaped by evolution cf. basal cognition, cognition
Biological goal - the object towards which the behavior of a biological agent is directed. Biological goals are the natural ends or limits of internally generated biological processes that follow transparent causal pathways - the development of a structure, maturation of an organism etc. Their sources may be mindless, minded but unconscious, or conscious. Short-term proximate goals serve long-term ultimate ends. Goal-directedness confers both purpose and agency. Biological goals are usually observed and studied as the behavioral outcomes of internal processes.
Biological object - something from the living world that can be studied scientifically; taken to be either a structure (whole or part), process, or behavior
Biological principle - an underlying regularity of a biological system e.g. evolutionary principles (like natural selection), agential principles (survival, reproduction, adaptation, evolution), biochemical laws (like the laws of thermodynamics), or ecological principles (like the cycles of matter and energy flow). By understanding these principles, scientists can make predictions about biological outcomes and develop theoretical frameworks that explain how and why organisms behave and evolve in particular ways.
Biological simile – a comparison (likeness) of biological phenomena that is based on real evolutionary connection
Bioteleological realism - the claim that purposes exist in nature and that most cognitive metaphors used in science are grounded in non-cognitive biological facts
Biosemiotics - the study of the production, interpretation, and communication of signs and meanings in living systems
Bioteleology - purpose resides in the fact that there are natural ends or limits to biological processes (e.g. the maturing of an acorn into an oak tree; the termination of a mating ritual in copulation), that these ends are objectively  goal-directed and therefore purposive. Teleonomy controversially interprets teleology as implying a metaphysically questionable source of purpose. The word teleonomy attempts to replace this purported implication with a naturalistic explanation. The distinction between teleology and teleonomy, and whether that distinction is warranted, remains unclear
Cognition - the internal processing that precedes and guides the behavior of biological agents; the goal-directed and adaptive process of acquiring and interpreting information about the conditions of biological existence;  the acquiring, processing, storing, organizing, prioritizing, and communication of information. In its highly evolved and limited human form, it involves perception, memory, reasoning, and problem-solving, allowing individuals to understand their environment, make decisions, and establish knowledge through experiences and interactions with the world cf. basal cognition, biological cognition
Cognitive ethology – the study of the influence of conscious awareness and intention on the behavior of an animal
Cognitive metaphor - a metaphor used in the context of human intentional psychology. When we have no words to describe real pre-cognitive agential traits, we resort to the language of human cognition, thus condemning these traits to the figurative world of metaphor
Complementary properties – the properties instantiated by the relata of a biological simile
Conditions of existence (biology) - those factors influencing the inner processing of organisms including triggers arising from both inside and outside the organism.
Derived concept – a concept with a narrow semantic range
Emergence - as used here - the origin of novel objects, properties, or relations in the universe that warrant human categorization
Environmental factors - the external factors impacting on the existence of an organism
Evolutionary biology – the study of evolutionary processes (notably natural selection, common descent, speciation) that created the community of life
Fitness - a measure of reproductive success (survival) in relation to both the genotype and phenotype in a given environment
Function - also referred to as adaptive significance. Typically, this is the role that the structures, processes, or behaviors of an organism play in the functional organization of the organism as a whole. It helps to regard these characters of organisms as having functions while organisms themselves, as independent agents, have purposes and goals
Genotype - the genetic constitution of an individual organism, encoded in the nucleus of every cell
Grounding concept – the general ideas that underpin more specific (derived) concepts
Heuristic – stimulating interest and investigation
Holobiont – an aggregation of the host and all of its symbiotic microorganisms
Homeorhesis - (Gk - similar flow) a term applied to dynamic systems that return to a specific path or trajectory, in contrast with systems that return to a particular state (homeostasis). Homeostasis refers to the maintenance of a stable internal environment in response to external changes (e.g. body temperature in mammals) while homeorhesis is the adjustment, sometimes changing over time, to meet particular organismal functions or goals (e.g. changes in blood composition that support the fetus during pregnancy).
Homology – a similarity in the structure, physiology, or development of different species of organisms based upon their descent from a common evolutionary ancestor
Human agency - behavior motivated by conscious intention; the uniquely human specialized form of biological agency that is described using the human agential language of intentional psychology; the capacity to act based on reasons as cognitive and motivational states (beliefs, desires, attitudes) (philosopher Kim)
Human-talk - the language of humanization - the attribution of human characteristics to non-human organisms, objects, and ideas. (Biology) the description of non-human organisms using language that is usually restricted to humans and human intentional psychology; the use of cognitive metaphor to describe non-cognitive but real biological agency; the psychologizing of adaptive explanations
Intention - a cognitive goal, or pre-cognitive behavior that is directed towards objects, properties, or states of affairs
Intentional idiom - the use of intentional language in a wide range of contexts including those relating to non-human organisms
Life – units of matter with the agential capacity to survive, reproduce, and flourish (cf. biological axiom) as best exemplified by autonomous organisms. Life processes, such as growth, reproduction, response to stimuli, and metabolism are subordinate to the organismal wholes of which they are a part
Metabolism - the set of processes that sustains an organism (or, more generally, any biological system)
Metaphor - figurative language as ‘nonliteral comparisons in which a word or phrase from one domain of experience is applied to another domain’. An 'as if' direct (not a 'like') comparison that is not grounded in reality e.g. 'You are a rat'.
Natural agency - any agency in the natural world
Natural purpose - the natural goals, ends, or limits of biological agents, both cognitive and non-cognitive
Normative realism - the view that normativity has its origin in biology through the mindless and mindful ultimate goals of survival and reproduction, and proximate goal of flourishing
Organism - unicellular to multicellular life forms that include fungi, plants, and animals. The mostly physically bounded and functionally organized basic unit of life and evolution. As a mostly autonomous biological agent the organism acts on, and responds to, its conditions of existence with flexible but unified and goal-directed behavior that demonstrates the objective, ultimate, and universal propensity of organisms to survive, reproduce, and flourish. While life can be described at many scales and from many perspectives (and the structures, processes, and behaviors of organisms all demonstrate a degree of autonomy), it is the entire organism that provides the agential reference point of life - whose autonomy is both intuitively and scientifically most discrete. Exceptional cases such as lichens, Portuguese Men-o-War, the Great Barrier Reef, sexually aberrant variants etc., do not erode these core characteristics.
Organismal factors - the internal factors impacting the existence of an organism
Personification - the representation of something in the form of a person
Phenotype - the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment
Physical reductionism - the view that biological phenomena can be adequately explained in terms of physico-chemical entities
Pre-cognition - all organisms are goal-directed autonomous biological agents that act on and respond to their conditions of existence in a flexible way. Agency is usually associated with human cognitive traits like intention and deliberation. However, the presence of agency in non-cognitive organisms confirms the presence of non-cognitive agential traits, a characteristic of non-cognitive organisms that distinguishes them from inanimate and dead objects. These non-cognitive agential traits are referred to here as pre-cognition.
Process ontology – it is processes that create phenomena including emergent and ephemeral ‘things’ which are derived from processes as transient and cohesive patterns of stability within the general flux. Thus, things are derivative of processes. In practical terms this does not mean that things do not exist or are not useful concepts. However, instead of thinking of processes as belonging to things, it is more scientifically informative to think of things as derived from processes. Organisms are prime examples of transient things in process
Proximate explanation - an explanation dealing with immediate circumstances
Purpose – the reason (end, aim, or goal) why something exists or is done, made, used etc.; (biology) the goal of a biological agent, paradigmatically a living organism, but also the natural end-state, limit, or reason for a structure, process, or behavior (often referred to in this sense as a function). In humans, purposes can assume a cognitive form as mental representations (conscious intentions); what something is 'for'; Aristotle's final cause or telos. Purposes, as the goals or ends of organisms and their parts, are an emergent and agential property of life that preceded human cognition: causal (etiological) explanations of purpose do not explain it away. Darwin did not remove agency and purpose from nature, he showed how they generated a process of natural selection. Thus purpose, in a broad sense, is what a structure, process, or behavior is ‘for’ – its function, reason, or intention – its adaptive goal. In a narrow human sense, a purpose is the object of conscious intention. A distinction of convenience may be made between the functions of parts (the role of a part within a whole), and purpose (the 'function' of the whole organism - as biology’s canonical agent
Relata – the objects being compared
Semantic range – the degree of generality or abstraction encompassed in the meaning of a word - range of objects and ideas encompassed by its meaning
Synapomorphy - a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants
Teleology - the philosophical concept of purpose and design in the natural world. The claim that natural phenomena occur for reasons as natural ends or purposes that are neither necessitated by human or supernatural intention nor implying backward causation or foresight. For teleology in biology see bioteleology. The article on bioteleology discusses 8 senses of 'teleology'
Teleonomy - see bioteleology
Trait - a unit of the phenotype (physical or behavioral)
Ultimate explanation - a long-term, often evolutionary, explanation (e.g. in biology the purpose or measure of fitness of a particular trait)
Umwelt - an agent-centric orientation to the world; the environment of adaptive significance for a particular organism - its unique perspective or 'point of view': those factors important for its survival, reproduction, adaptation, and evolution: its mode of experience or 'reality'. For humans, this is the commonsense world of everyday experience (cf. manifest image) that is mostly a consequence of our innate mental processing which is, in turn, a consequence of our uniquely human evolutionary history
Values – (biological agency) that which ultimately motivates the behavior of biological agents (living organisms), namely the universal and objective goals of the biological axiom. Human agency - the proximate and subjective attitudes, beliefs, and inclinations that guide human behavior

Life is . . .

. . . not being dead
. . . greater than the sum of its parts
. . . complex chemical organization
. . . different things to different people
. . . a mystery
. . . a journey
. . . don’t know
. . . a mission to help other sufferers
. . . what you make it
. . . life begins after death

Kristine Kerr, Gourock, Renfrewshire

To which it may be added that death is no mystery because:

. . . life after death is the same as life before birth

– – –

First published on the internet under heading ‘Life as agency’- 1 March 2019

. . . 24 August 2022 – substantial revision into the form What is life?
. . . 12 December 2022 – revision and addition of concluding paragraphs
. . . 21 February 2023 – end of an extended period of revision – assessing consistency across related articles
. . . 6 June 2023 – added definitions to heading and section on biological explanation
. . . 7 October 2023 – starting a revision with more emphasis on an alternative definition
. . . 12 August 2024 – edited introductory material and added Biological Revolution box and biological agency glossary

Purposeful (goal-directed, functional) structure demonstrating biological agency
Shared X-Ray image of stingray by loctrizzle http://imgur.com/gallery/bZbHmJA