The swarming, ever-changing character of the living world challenges our deepest assumptions about the nature of reality.
If philosophy is a tree, metaphysics and epistemology are its two main branches. Epistemology asks how we can know about the world; metaphysics tries to figure out what the world is, at its most fundamental level. If our tree fell down in a forest and no one was around, the epistemologist would set about examining the quality of the evidence for what happened; meanwhile, the metaphysician would wonder if it made a sound.
Philosophers of science (like me) usually take the existence of things and events for granted. We do epistemology: we focus on knowledge, not the thing itself. We ask ourselves questions such as: why is science so successful at finding stuff out, if indeed it is? Is there a method that underlies this success? How do values shape scientific enquiry? Mainstream metaphysics keeps us in our place, generally saying that the scientific endeavour is just too narrow to address profound questions about existence, being and reality.
But I’d argue science is precisely where we should start to answer these questions – in particular, with the weirdness and complexity of biology and biochemistry. From the origins of cancer to the nature of personal identity, the life sciences do not merely provide us with ever-greater numbers of disconnected facts. They also offer us the best data for putting together a broader picture of what the world is really like, a picture that confounds many common assumptions about what things are and where they come from.
When we first pull a fish out of the sea, we might wisely remain agnostic about how such an unusual entity got to be there. After thousands of fish of many different kinds, we are entitled to infer that there is a whole strange, living world down there under the waves. Similarly, since science aims to discover truths about the world, surely it should tell us something about the very deepest levels of our reality, which is to say, metaphysics.
This project of science-based metaphysics, sometimes referred to as ‘naturalistic metaphysics’, has been surprisingly controversial. The philosophers James Ladyman at the University of Bristol and Don Ross at the University of Cape Town offered a forceful defence in their book Every Thing Must Go (2007). As that book illustrates, the debate can be technical and vitriolic. Consequently, I won’t defend naturalistic metaphysics from its critics so much as show you how it helps us inch towards an answer to one of the oldest chestnuts in the history of philosophy: is reality made up of things that somehow change over time, or are things just temporary shapes that our perception plucks out from a flux of unruly, unfolding processes?
A good place to begin is with the question of essentialism. An ancient philosophical tradition dating back to Plato and Aristotle sought to discover essences, the defining properties of things – ‘the being of any thing, whereby it is, what it is’, as the philosopher John Locke put it in An Essay Concerning Human Understanding (1689). Locke doubted whether we would ever be able to discern such essences, lacking the necessary ‘microscopical eyes’ to discover them, although he did not doubt that they were real.
But is there really some inner nature that makes a frog a frog, and something else that makes a toad a toad, and an unbridgeable gulf in nature between the two? Or are these just words that make more or less pragmatic divisions among the denizens of the natural world, divisions that might equally well have been made in substantially different ways? For naturalistic metaphysicians, this is a question that must in the end be answered from empirical experience, or science.
We can make the stakes of essentialism more concrete by looking at the case of proteins. These are the worker-bees of the organic world, responsible for everything from ferrying signals between cells to kickstarting chemical reactions. They’re made up of long molecules known as amino acids, strung together in chains and folded into fiendishly complex shapes.
So just what is a protein? Scientists used to think that they could define each kind of protein by figuring out its sequence of amino acids, mapping the structure or form, and observing how the combination of these properties allowed the protein to serve its specific physiological function. Unfortunately, things aren’t quite that simple. A well-worn metaphor is that a protein (in the form of an enzyme) works like a ‘lock and key’, fitting just-so into whatever it’s acting on. Yet increasingly it looks as if the two actually accommodate one another, less a key in a lock than a negotiation on the fly. Moreover, various types of proteins can ‘moonlight’, doing different things in different situations. Their abilities often depend on their context.
Phosphoglucose isomerase is best known for its role in the process that releases energy inside cells, for example – but when outside the cell, it can perform at least four distinct functions, such as promoting nerve growth. Worst of all for categorical purists was the discovery of ‘intrinsically disordered proteins’, shapeshifting macromolecules that rapidly switch from one form to another. Current estimates suggest that 40 per cent of eukaryotic proteins could behave this way, and 10 per cent of proteins overall.
Evolution tells us that, if we take a wide enough perspective, there are no sharp lines between species