Most philosophers, if asked what were the most basic constituents of their ontology, would probably name things and properties. The former may be simple – atoms – or complex, composed of other things. The latter may be of the kind predicable of individual things, or they may involve relations between things. But the idea that a true description of the world will say what things there are and what are their properties is a natural and plausible one. Even if, like the Wittgenstein of the Tractatus, we hold that the world consists of “facts not things”, facts are generally supposed to obtain when things have properties.
There is, however, an alternative ontology, one generally attributed in antiquity to Heraclitus, that takes things themselves to be only temporary manifestations of something more fundamental: change or process. As Heraclitus put it, “There is nothing permanent except change.” On such a view what we think of as things are no more than eddies in the constant flux of process. While I won’t try here to argue for the general superiority of this latter view to the more conventional ontology of things and processes, I do want to claim that an ontology of processes is better suited to understanding the nature of life and the living.
Reflection on the last hundred years of physics might lead one to suppose that the ancient debate as to whether the world was ultimately composed of things or processes had been resolved in favour of the latter. Quantum physics, whatever else it may do, seems to constitute a decisive rejection of the atomism at the root of traditional thing, or substance, ontologies. My interest, however, is in larger scale entities, those that are the subject matter of biology. Within this narrower sphere the basic parameters for most subsequent thought were laid down by Aristotle, and the Aristotelian tradition is firmly on the side of things rather than processes.
Organisms were for Aristotle the standard exemplars of what he called primary substances. A primary substance was a thing of a particular kind, for example a cat. Particular cats, such as Tabitha, are assumed to have sharp boundaries: everything is either part of Tabitha or not. Subsequent substance-based thought about the living world has seen substances as forming a hierarchy. Cats are composed of organs, organs are composed of cells, etc., and cats might themselves make up larger entities such as species.
A central question that arises inevitably in the Aristotelian framework is what it is that makes some entity an entity of a particular kind, and hence also, what it is that determines whether an entity remains the same despite changes that it undergoes. Both questions have traditionally been answered by appeal to an essential property or properties, characteristics that are necessary and sufficient for something to be, say, a cat. But as many philosophers have noted, the fact of evolution makes the postulation of any such properties problematic. There is no clear limit to how much an evolving lineage may change, or in what respects, and any supposed essential property will make possible bizarre events of the sudden appearance of alien individuals in an evolving lineage: some of Tabitha’s kittens might happen to lack an allegedly essential property and, therefore, would not be cats, a possibility that contradicts most biological thinking about the nature of a species.
Aristotle, it is true, seems to have had the insight to realise that the essence of an organism was something dynamic, a developmental trajectory or life cycle. But this does not resolve the conflict between essence and evolution. Life cycles are just as much subject to evolutionary change as anything else; indeed, on some influential views they are the most important sites of evolutionary change.
Against the tradition of substance thinking an important minority of philosophers have followed Heraclitus in espousing more processual views of reality. These include such major figures as Leibniz and Hegel, but the definitive exposition of a process-centred metaphysics is in the work of Alfred North Whitehead, for example in his classic, Process and Reality. Nevertheless, in the metaphysics and philosophy of science this tradition has had very little impact in recent years. My current ERC-funded project, “A Process Ontology for Contemporary Biology”, aims to redress this balance. The position I propose to defend in this work is that the most illuminating perspective on living phenomena is as a hierarchy of deeply intertwined processes, processes that are shaped by both higher and lower level processes with which they are connected.
One common statement of the difference between a substance- and a process-centred metaphysics is that the former sees being as basic, and the latter prioritises becoming. For Aristotle, as already noted, substance was closely connected to essence: to be a cat was to possess the essence of catness, the property or properties that made that entity a cat. For a processualist, on the other hand, a cat is a pathway from zygote to kitten to mature animal to death. It is not, as the processual interpretation of Aristotelian essence suggests, that undergoing a developmental sequence is a property necessary and sufficient for being a certain kind of thing, a cat. For the process ontologist the cat just is the process connecting this sequence of stages. Any time slice of this sequence can only be properly understood as part of this longer process, and in terms of both its preceding history and its possible future trajectory. No property need be common to every stage of a cat life cycle; it is rather the relations, presumably causal, between stages in its history that constitute it as a cat. And there is no particular sequence of stages a cat must pass through. To be a cat is to be connected to a process which, in turn, is connected to the lineage (process) that constitutes the cat species.
For a substance theorist, what require explanation are the changes that occur to an entity, and the conditions under which an entity can remain the same thing through change. The latter question is most visible in the longstanding debate about personal identity: in what sense can I be the same thing as the foetus or infant from which I originated, given that neither my matter nor my properties have remained the same? For a process theorist, on the contrary, the central questions concern rather how a combination of processes can maintain the appearance of (some degree of) stability and persistence in an entity that is fundamentally only a temporary eddy in a flux of change.
The differences between these basic metaphysical views can be seen most clearly with respect to the concept of an organism, generally assumed to be the central kind of biological individual. As already noted, an Aristotelian substance metaphysics assumes that things have determinate boundaries. Intuitively, this seems exactly right for a paradigmatic organism such as Tabitha or Aristotle. While it is no doubt possible to modify this assumption and allow for some fuzziness about exactly where an entity begins and ends, this hardly seems a serious problem with regard to such exemplars.
However, the growing appreciation of the omnipresence of symbiosis shows that even this intuitive judgement is problematic. All, or almost all, animals co-exist with vast swarms of bacteria, in the gut, on the skin, and in all the bodily orifices. These are not just opportunistic occupants of comfortable niches, but many of them are vital to the well-being of the animal. In the case of humans, in which symbiotic microbes outnumber human cells by an order of magnitude, these have been found to be involved in digestion, development, immune responses, and very likely much more. Are these parts of the animal or distinct organisms? Or is this, rather, a question the answer to which will vary with the context of enquiry?
In fact the reliability of intuitive judgements on such questions has long been called into question. Groups of trees may originate in many species from underground roots from which new shoots can appear above ground. In such cases, all the trees may be part of a single connected vegetative system, and the intuitive judgement that a tree is an individual may be rejected. On the other hand from some perspectives, for example ecology, it may be that the individual tree is indeed the salient individual.
Another case that has been widely discussed is that of the social insects. A worker bee is intuitively an organism, but in fact it has no viability or reproductive potential on its own. It is often said that the real organism is the colony or hive, sometimes referred to as a superorganism. But then consider an organism such as the leafcutter ant. The system of which an individual leafcutter ant is part depends as much on the fungal colony that digests the leaves that are its food as it does on other ants in the colony. This fungal colony, in its dedicated chamber, is often described as the colony’s stomach. Moreover the fungus, in turn, depends on a consortium of symbiotic bacteria that provide equally necessary metabolic contributions to the digestive process. And so on. Which of these entities should be considered parts of the superorganism?
From the point of view of organisms as substances, with determinate boundaries and well-defined persistence conditions, these questions may well seem unanswerable. An ant colony stomach, for instance, would appear to be too intimately dependent on the ant colony to which it belongs to be an independent substance. Yet individual fungal cells function only as part of this system which, in turn, can survive only when situated in the wider ant colony. Within such a complex and interdependent system the attempt to identify sharp boundaries between the “things” that constitute it seems profoundly at odds with the reality we confront.
Considering these systems as sets of intertwined processes, on the other hand, makes much better sense. The omnipresence of symbiosis suggests that isolating traditional organisms from the complex set of relations that are required for their persistence is better seen as a pragmatic exercise for particular purposes. As mentioned above, 90% of the cells in a human body, are microbial symbionts, huge numbers of which are required for the healthy functioning, and others of which have more or less cooperative relations with the whole system or important subsystems. And humans are probably as close as one could get to a traditional biological object with sharp boundaries. In general, it seems increasingly plausible that there is no unique way of distinguishing biological things from the multiple higher and lower processes by which they are sustained. I take this as evidence for the hypothesis that the ontology of biological things is less fundamental than that of living processes.
Does this very abstract issue matter to our understanding of biology? Of course part of the answer is just that we would like to know how things are. Metaphysics has value in its own right. But I also believe that adopting a process-centred approach can make a difference to quite practical questions in biology and beyond. I shall briefly sketch some examples to illustrate this claim.
My first example is the understanding of the nature of the genome. One of the deepest problems in biology is to explain development, the process by which organisms reliably grow into organisms of the right kind. Dogs give birth to puppies not snakes or cabbages. Preformationism, a solution to this problem often illustrated by quaint seventeenth-century pictures of tiny babies squatting in the head of a sperm is an attractive solution to this problem: the structure of the adult is there from the beginning. The seventeenth-century version does not, of course, look plausible today, but not long ago genomes were widely seen as offering a sophisticated version of such a solution. The actual structure of the adult was not there from the start, to be sure, but in the genome we could find a programme or a blueprint from which the organism could be constructed. Dogs give birth to dogs because they pass this blueprint to their puppies. Not coincidentally, the genome on such a view was often interpreted as providing the essence of the organism in which it resided.
This interpretation of the genome sees the genome as a stable thing with remarkable properties that somehow encode or represent the future organism. But it is now clear that the genome is, on the contrary, itself an entity in constant flux, a process, I would say, rather than a thing. Although nucleotide sequence is a highly stable feature of genomes, even this is maintained as such by a range of editing and repair processes. Moreover, the function of the genome is constantly sensitive to interactions with a variety of molecules in the cell which, in turn, change the physical structure of the system in ways that determine what genes are expressed. The same genome as well as giving rise to a huge variety of different cells in the same organism, can be involved in the production of many very different organisms, a phenomenon studied under the rubric of phenotypic plasticity. The genome, in short, is a fully interactive participant in cellular processes. The failure of the idea of genome as blueprint is no longer very controversial among well-informed scientists, though it appears to persist with little change in the wider public.
A second issue that is potentially transformed by a processual perspective on living systems is the distinction between structure and function. It is common to think of biological objects having particular structures that enable them to perform particular functions. But if these “objects” are in fact constantly fluid and evolving processes, this perspective can be misleading. Structure and function are intertwined aspects of process. A good example of a phenomenon that illustrates such a view is plant development. The growing meristem of a plant is typically an opportunistic growth process capable of producing a variety of structures – leaves, flowers, roots – in response to the environment it encounters. These putative structures are traditionally understood as distinguished in virtue of the particular functions – photosynthesis, attraction of pollinators, absorption of nutrients – they serve. But even the attempt to distinguish sharply between these traditional morphological elements is often problematic. One often encounters claims such as that the colourful bracts of Bougainvillea, or the spines of a cactus, are really leaves. But given the totally unrelated functions and structures of these entities, and the general plasticity of plant development, it is hard to make sense of such claims. Better, perhaps, to say with J S Haldane in his 1931 book, The Philosophical Basis of Biology, “[s]tructure and functional relation to environment cannot be separated in the serious scientiﬁc study of life, since structure expresses the maintenance of function, and function expresses the maintenance of structure”; or with the founder of General Systems Theory, Ludwig von Bertalanffy, functions are fast processes and structures are (relatively) slow processes.
In the world of molecular biology, proteins are the paradigmatic examples of biological entities for which structure is assumed to determine function. However, this simple structure/function analysis of proteins has had increasing difficulty as it has been found that many proteins serve a range of functions (“moonlighting” proteins); that many or most proteins do not have a fully determinate structure (“intrinsically disordered” proteins); and that the interaction between an enzyme and the molecule with which it interacts, does not really fit the traditional “lock and key molecule”, but rather involves a considerable amount of mutual configuration. All of these phenomena fit better into the view of the protein molecule as a dynamic entity, the causal powers of which are constantly being reconfigured in relation to the processes in which it participates, than into the classical model of a thing with a fixed nature that determines once and for all what it is and what it can do.
A processual perspective on biology has implications for philosophy that go well beyond the philosophy of biology proper, most obviously for questions that bear on our understanding of the human. Consider, for instance, the topic of personal identity. Recently there has been a move to challenge traditional Lockean accounts that ground the persistence of a person in psychological continuity, most importantly mediated by memory, with so-called “animalism” the idea that persons persist just as long as does the human animal with which the person is associated (by identity, spatio-temporal coincidence, causal dependence, or whatever). I find this idea appealing. However, its successful elaboration will depend, obviously enough, on an adequate account of what it is for an animal to persist; and this, I have suggested, is a more difficult question than is often supposed.
The process normally identified as a human individual is certainly one that can easily enough be distinguished from both the lower and the higher level processes that sustain its continued existence and development. The point is not to encourage scepticism about the existence of human animals, but rather to point out that the notion of this we typically assume is to some degree optional. In a different and perhaps simpler kind of social organisation we might see the family, or the village as more fundamental than the individuals that at any time compose these larger groups. In our contemporary more atomistic and anomic societies, it is easy to forget the extent to which the individual is a process only made possible by an enormous web of connections with other individuals. Process philosophy of biology has powerful resources for challenging the radical individualism that is so widely taken for granted in contemporary views of the social.
Perhaps even more controversial implications arise in connection with what the philosopher of medicine Elselijn Kingma characterises in ongoing work as the metaphysics of pregnancy. We often think of a foetus as a kind of thing in a box; vulgarly, as a bun in the oven. But suppose we think rather of the mother and foetus as two profoundly intertwined processes, gradually diverging from one another? This divergence, incidentally, is far from complete at the moment of birth as the processes of mother and child continue to be deeply interdependent. This picture, more coherent with the biological reality I would argue, has profound implications. One might argue, for instance, that abortion is better seen as a kind of elective amputation than as the termination of an independent entity.
As a committed pluralist, I am reluctant to assert dogmatically that the world is composed of processes not things. Sceptics about the possibility of drawing metaphysical conclusions from empirical facts may prefer to interpret my observations as offering only (at best) an illuminating alternative framework for thinking about living systems. However, I am confident that a process ontology (or framework) does provide a generally more illuminating view of the living world, and certainly something similar seems true of contemporary physics. At the very least the question whether things or processes provide a better framework for interpreting science is one that should be a central concern for anyone interested in the metaphysics of science. And perhaps it is a question that matters beyond just getting to the truth. As Whitehead wrote in Process and Reality: “There is urgency in coming to see the world as a web of interrelated processes of which we are integral parts, so that all of our choices and actions have consequences for the world around us.”