Nearly every era decries the anthropomorphizing definition of life assumed by previous periods. Definitions of life are often concerned with defining what is human: some historical periods assume a wider, others a narrower, scope for the term. In recent decades, debate over when human life begins, what rights inhere in it, and how it might end have seen life become a polarizing term in the public sphere.
According to the OED, the primary meaning of life is “animate existence.” Its medieval usage, however, was quite broad, encompassing a variety of material and immaterial meanings. It referred to the “vital spirit” that animated earthly bodies, as distinguished from the natural and the animate spirit often thought to reside in the heart as opposed to the brain. By extension, the word also referred to the material body as a whole. In medical and scientific treatises, lif could also refer to the material custom that shaped a body, diet, or a regime. In this sense, the term designated nurture rather than nature. But Middle English lif could also refer to purely spiritual, immaterial aspects of life, when it was used to translate L anima, “soul, breath.” Moreover, as the usual translation for L vita and oF vie, “lif ” designated, of a saint’s life, a moral example that provided a pattern for spiritual existence. When the drunken Miller of Chaucer’s Canterbury Tales announces that he will “telle a legende and a lyf / bothe of a carpenter and of his wyf,” (3141–2), he prepares us for a hagiographic satire that revolves around not a holy exemplar but around an adulterous wife, wily clerics, and a hard-done-to peasant. Medieval lif was simultaneously a thing (sustenance; a body or essence), a disciplinary practice, a mode of life, and a spiritual model. Its meanings fell along a finely graded continuum that ran from the utterly physical to the transcendent, including most points in between.
The broad and continuous nature of these meanings is reflected in medieval beliefs about what qualifies as “animate,” a definition that differs markedly from modern ones. In current usage, the OED defines life primarily as “human or animal existence, cf. soul.” This definition restricts it to these categories of being. In medieval scholastic philosophy, by contrast, lively existence and, indeed, soul were shared among many ontological categories. Following Aristotle, medieval nature was defined as anything that possessed self-motion. For example, rocks were thought to fall to the ground not on account of the law of gravity but because they followed their natural inclination to return “home” to their rightful place in the earth. In this way objects that moderns recognize as inanimate possessed quasi-animate powers of motion. Plants were thought to have souls in the sense that their motion was directed toward a particular end. The human soul contained within it vegetative and animal souls, in addition to the uniquely rational human one. Life was therefore a much broader category than we recognize today.
The definition of life narrowed considerably in the early modern period, when the word began to be restricted not just to those things that exhibited motion, but also to that immaterial nous that supplemented, rather than inhered in, matter. What had been an inner principle of growth and change was now outsourced: imagined as an exterior force that supplied the links between otherwise unrelated parts. The scientific innovations of Gassendi and Descartes led to the mind-body dualism that tightened the circle of life to include only intentionally conscious existence, leaving plant and animal alongside the inanimate rock in the shadows. A corollary of the mechanical philosophy saw the human as res cogitans (the thinking thing), while the rest of the world was lumped together into res extensa (the extended thing or corporeal substance). This definition famously led to animals being excluded from the charmed circle of life by Descartes, who concluded that since animals lacked consciousness and could suffer no pain or pleasure, they were, in effect, only machines or automata. What made this belief about animals possible was a new belief in the identity of soul and rational mind— an identity that excluded mere life.
In C19, discussions of life shifted away from the early modern emphasis on life as soul or consciousness. Darwin equated life with genetic adaptation, and in particular with reproduction rather than observable sentience or vitality. The scientific drive to redefine life as a physiological process that could be broken down into its respective parts—life as behavior rather than essence or soul—was the result of a long process that existed dialectically with an opposing conception of life that, following Spinoza, saw the world as a singular living being, disposed to isomorphism and homology in all its aspects. The effect is what the historian of evolutionary biology Robert J. Richards has called a “romantic conception of life,” tracing in the writings of Goethe, Schiller, and others an ideal that sought a holistic, cooperative conception of life without Aristotelian teleologies. This tension between the monist celebration of life and a particulate science is reflected in Mary Shelley’s Frankenstein, for instance, a work that long before Darwin had already raised the question of what our moral obligations are to living creatures, especially creatures to whom we have given life. Shelley’s Frankenstein also raised the specter of biohorror, the risks and consequences of life gone bad.
These poles continued to shape scientific definitions of life in subtle ways, for example in remediated form in attempts to define life in genetic terms in the work of physicists and molecular biologists such as Erwin Schrödinger, Freeman Dyson, and others. Their attempts to define what life is can be (no doubt simplistically) boiled down to the question: Is life guaranteed by relentless replication of the “selfish gene” (in Richard Dawkins’s phrase) or by the cooperative homeostasis necessary for maintenance of the genome as a whole (Dyson’s view)? Behind this question we can dimly perceive C19 terms: Is biological life holistic and communal (Spinozist) or ruggedly individualist (Darwinian)? What is significant is that whatever answer is chosen, both of these interpretations of life in terms of genetics are modelled on identifiable human behaviors. Whether we understand genes as essentially selfish or essentially cooperative, in both cases we understand them in terms of human agency.
Our contemporary understandings of life have been largely shaped by this disjunctive linguistic and philosophical inheritance. The particularly C19 tensions between biological and theological definitions outlined earlier subtend current public debates and educational policy regarding topics including evolution, abortion, capital punishment, euthanasia, and end-of-life care, since most of these debates center around how far certain rights can be said to inhere in life itself. Such ongoing mobilizations of life suggest that, as we consider the contemporary ethical and political implications of scientific innovation, it remains useful to look back to earlier moments where the line between the human and the natural was imagined in ways that continue to influence how we now understand what it means to be human.