Cats don’t actually have nine lives.
Of course, you probably already knew that. Cats, like all biological beings, have only one biological life. It’s unique and discrete, and when it comes to an end, that’s it: kaput. That, at least, is how we typically think about lives: every organism has one and only one of them – there are no back-ups.
And since humans are biological beings, what’s true for cats is true for us as well. I have one life. You have one life. You may “lead different lives”, but that’s just a turn of phrase. I may have a “secret life” or a “private life”, but those are turns of phrase as well. Maybe you believe in an “after life”? Fine – but the clue’s in the name: whatever that is, it’s not a life, it’s something else, which comes after. The sad reality is that when your biological life ends there are no seconds. Sorry.
Furthermore, there are depressingly myriad ways for these lives of ours to stop: asphyxiation, bombs, cannibals… death, in short. There are many changes that biological beings like you and I simply cannot suffer. And this is worrying because, for many of us, there’s a sneaking suspicion that the continuity of our biological lives is of great importance to our continuity. Losing a life is not like losing one’s hair; the former seems to prejudice against one’s survival, the latter does not. As noted, some theists believe we can survive our deaths in non-corporeal form – but many of us think that the end of our biological life marks the end of our existence.
It’s not surprising, therefore, that throughout human history a considerable amount of time and effort has been spent trying to preserve lives, and to prolong them. In the last hundred years or so, scientists have made great strides in this endeavour (in humans, at least). In the UK, where the benefits of the latest medical technology are widely enjoyed, the average life-expectancy has increased from around 70 to 80 in the last forty years. Drug therapy has contributed to this. So has transplantation; if a valve in your heart stops working, you can take “spare parts” from another human, or a non-human animal like a pig. Similarly, “life-support” machines can now sustain patients in “vegetative” states, aiding respiration and other vital functions.
Yet oddly, these advancements – ostensibly aimed at lengthening life – have begun to put pressure on exactly what we mean when we talk about “life” and its partner concept, “death”. We mightn’t agree with them, but we understand people who, when looking at patients in persistent vegetative states, say, “That’s not living”: they’re expressing a concern about a technological intrusion into a singular, and singularly important, biological process. The thought is that whatever is being supported by so-called “life-support” machines is not life as we normally understand it.
But how do we normally understand it?
Technological interferences encourage us to reassess apparently commonsensical thoughts about what it means to be “living” – and sometimes our views end up changing to accommodate scientific revelations. We find a clear example of this at the medico-legal level, with the relatively recent nomenclature of “brain death”. Until the twentieth century, medical and legal communities thought of death as the permanent loss of certain central biological functions, like heartbeat and respiration – but following the advent of life-support machines and cardio-pulmonary resuscitation the criteria have changed. For medico-legal purposes, an individual is now deemed dead when examination shows complete and irreversible absence of brain function. (In the UK it is specified that death is determined by the irreversible absence of brain stem function, not just the cessation of activity in the cerebrum (“cerebral death”).)
When we train our attention more closely on our concepts of life and death, they become strangely blurred. It’s hard to articulate them. And yet it’s hard not to try to pin them down, not simply as a dry, academic exercise, but because we have a special, vested interest in these notions. We – you and I – are living beings; many of us think our survival depends on the continuity of our biological lives, so it matters, on a very personal level, what counts as the cessation of a life. In the idiom of Anglophone philosophy we find questions borne from the philosophy of biology (“What is biological life?”, “What is an organism?”) intersecting with questions of “personal identity” (“What constitutes my persistence?”, “What, fundamentally, am I?”). Academic philosophy is often found to be far removed from our everyday concerns, but in these two areas at least, it seems it may help articulate and answer questions and worries situated firmly in the non-academic sphere. We care about what it means for us to stop existing.
There is a question, of course, about whether our survival really does depend on the continuity of biological life. From the seventeenth century onwards, the Anglophone “personal identity debate” has been dominated by the view that our persistence has less to do with biological activity than with psychological continuity. The locus classicus for this thought is John Locke’s Essay Concerning Human Understanding. In Book II of that text, he asks what it takes for us to persist through time and space; his influential answer is that since we are persons – thinking, intelligent, self-conscious beings – it is continued consciousness that constitutes our survival. We survive so long as our consciousness does. The thought has proven to be an incredibly durable one, and neo-Lockeanism remains the majority view in contemporary discussions of personal identity. When faced with canonical thought experiments, like “the Brain Transplantation case”, most Analytic philosophers say that psychological continuity trumps biological persistence. Individuals can survive such procedures (having one’s brain put into another individual’s body), though the organism does not.
There are, however, a growing number of philosophers who reject Locke’s analysis, and neo-Lockeans, or “psychological theorists”, are often contrasted with “biological theorists” or “animalists”. Animalists deny that we are fundamentally persons. They hold instead that we are fundamentally human animals, and that our persistence conditions are those of the human animals that we are. Whether or not we survive depends, not on a psychological relation, but on the continuation of biological life. One compelling reason for thinking this is the commonplace thought that you and I are not always conscious, and have not always been self-conscious beings, so we cannot be self-conscious entities fundamentally. At some point, for example, you were a foetus, and charming as such things are, they do not think, nor identify themselves as themselves; they are not persons. Instead, the animalists say, we are fundamentally animals, which survive as long as our biological lives persist.
Whether or not one subscribes to neo-Lockeanism or animalism, the notion of “life” is central to the personal identity debate in general – and it remains profoundly puzzling. Consider again, the case of the foetus (which the animalist says we once were), and the start of biological life. Technological advances allow us to peer into the workings of the human body – and the closer we look the more confusing things become. When exactly does life start? When the sperm meets the egg? When the zygote can no longer divide? When the infant can survive independent from its mother? The last surely relates to the skill of medical professionals, and the effectiveness of their equipment in sustaining premature babies, and this is constantly changing. Does this mean the limits of biological life are constantly changing too? Is it up to us to set these limits? Again, it’s important to note that these questions extend beyond the rarefied fields of Analytic philosophy, into very pressing discussions about abortion, for example, and the use of foetuses in medical testing.
How can we precisify this discussion? How do we say exactly what life is? Numerous answers have been offered to this latter question, from a variety of disciplines and traditions – but not least among them is the one proposed by the physicist Erwin Schrödinger in a now famous series of lectures he gave at Trinity College, Dublin, in the early 1940s. These lectures (unironically entitled “What is Life?”) were aimed at answering the question by analysing the biological activity realised by organisms in physico-chemical terms – and the answer he advanced therein has profoundly influenced generations of philosophers and scientists alike.
Schrödinger’s approach was to turn to physics and chemistry to explain biological life, and his aim in those lectures was to articulate the idea of an organising molecule, which carries genetic information and issues biological directives for organic growth and development. The talks were not particularly original (the notion of an “aperiodic crystal” had been doing the scientific rounds for some time), but they were rendered well enough to make them mainstream. The organising molecule that Schrödinger discussed is the conceptual ancestor of the now ubiquitous notion of DNA.
It is in the wake of Schrödinger’s lectures that James D Watson and Francis Crick discovered the helical structure of DNA, theirs being perhaps the most well-known and best celebrated scientific discovery of the twentieth century. At the time, and since, their research was touted as the “discovery of the secret of life” (to quote a 1953 BBC news report). The secret of life: it makes a catchy headline, and suggests that an answer had been found to the titular question of Schrödinger’s lectures.
The answer, in broom-broad brushstrokes, is roughly that life is nothing more than a collection of tiny things interacting in certain ways, according to organisational directives laid out by human DNA. According to Schrödinger, and those who followed him, biological life can be exhaustively explained in physico-chemical terms. This seems, incidentally, to be the account of biological life that underlies animalist discussions of the matter. The general impression one gets from reading texts like Eric Olson’s The Human Animal or Peter van Inwagen’s Material Beings, is that molecular biologists can, ultimately, furnish philosophers with an uncontroversial account of what a human animal is, and what conditions need to be met for it to persist, by examining the genetic “blueprint” or “instruction manual” contained within human DNA. The implication we find in these texts is that by consulting this genetic “plan” we can learn about what it means to come into and go out of existence. By consulting the human genome we (or rather biologists) can find out what biological life is.
Yet, in recent years, philosophers of biology have done much to demonstrate the failings of this kind of approach and the scientistic fetishism of human DNA. For one thing, they say, the biological processes that go on inside us emerge from the interactions between parts that exhibit massive genetic variation. Humans enjoy numerous, mutually beneficial relationships with vast numbers of endosymbionts – bacteria that line our guts and cover our skin. The processes that result from these collaborative relationships are far from unimportant (including digestion and immunological activity). The vital activities of our bodies are constituted by the cooperation between genetically diverse parts. (We see this even more dramatically in cases of colonial organisms, like slime moulds, corals, and medusae jellyfish, which are composed of colonies of genetically distinct polyp-like zooids.)
In addition to the ubiquity of symbiosis, philosophers of biology also point to the pervasiveness of genetic mosaicism and chimerism – where different parts of an organism have different genomes (for example, in calico and tortoiseshell cats). Much emphasis has also been put on the importance of epigenetic processes, and the heritable changes that occur that are not caused at the genetic level (e.g. methylation and histone modification). And all of this suggests that investigation into the human genome and its genetic directives is too narrow a focus. A human life seems to involve genetically various parts – and so the discussion of one genome cannot exhaustively explain the over-arching activity. The animalists cannot simply rely on geneticists.
Genetic heterogeneity is just one example of the puzzles that surround the concept of biological life, but there are many more. This apparently commonsensical notion is bewilderingly complex, and just as the microscope reveals innumerable beings inhabiting our bodies, so we find innumerable questions arising when we inspect biological life more closely. What do we think is essential to life, for example? Reproduction, metabolisation, an ability to self-repair? The natural realm is so astonishingly varied there are, more often than not, counter-examples to any definitive list of “vital” attributes. And what about the conceptual difference between “a life” and “life” (as in “life on Mars”) – can one conceive of one without the other? And what is the importance of our human conception of life? Is it problematically anthropocentric – do other creatures, with different perceptual abilities and different conceptual schemes, experience the natural world differently from us? Might life be better conceived as non-differentiable processes?
Faced with so many questions it’s easy to doubt the seemingly obvious everyday thoughts with which we started. How many lives do cats actually have? And how many lives make up your life? All of this obviously depends on what one means by “a life”, and in keeping with philosophical custom, my aim here has been to show that things are far more perplexing than at first appears without giving any answers. We normally think that lives possess determinate boundaries, but how can we find them? Biological investigation only makes things more confusing; we find that you and I may be composed of numerous different creatures – all of them possessed of what we would ordinarily think of as “a life” – yet at the same time each participates in some way in the great, orchestral symphony that we typically think of as our own life. Can lives overlap? Symbiosis seems to suggest they do.
We think that lives are natural occurrences; it is not – we say – up to us to define their boundaries, or to say how many lives different creatures possess. Yet technological advances – like life-support machines – also encourage us to question the naturalness of our concept of “life” and to interrogate exactly why we think about our existence in the way that we do. Are lives discrete events with natural limits, or is the concept of a life a human fabrication? Again, it’s not immediately clear.
Erwin Schrödinger proposed a reductionist programme by which we might be able to answer the question: what is life? Philosophers of biology are justly dubious about its all-encompassing explanatory power. It puts the cart before the horse; it tries to offer an explanation before accurately fixing on the explanandum. Genetic theory may tell us a huge amount about biological processes, but it won’t tell us how to define a life.
There’s another story that Schrödinger famously told – about a cat in a box that’s neither living nor dead. He used it to illustrate a point about quantum indeterminacy, but it illustrates another point just as well. What does it mean to have a life? What does it mean to lose it? It’s not clear in Schrödinger’s work, and it’s not clear in our everyday thought. Sometimes it’s not very easy to say whether something’s living or dead. And until we sort all this out, we’re going to have considerable difficulty finding determinate theoretical grounds for assessing claims about the lives of cats, let alone about our own.