What is life: why do we ask?

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Why do we continue to ask ourselves what life is? Why, that is, despite the imperfections of our responses, which require constant readjustment, have we always considered the distinction between what is alive and what is not so important? The need to distinguish, from the very beginning of evolution, between those who are similar to us—capable of acting with intent, cooperating, or posing a threat—has driven our species to develop increasingly refined criteria for recognizing others as living agents. In the African savannahs, recognizing a predator or a companion could mean the difference between life and death, and the human brain has developed rapid mechanisms for identifying purposeful trajectories and behaviors. From the first months of life, newborns show a preference and greater interest in self-referential movements, which unfold as if obeying an internal intention, and similar processes are found in flocks of birds or herds of social mammals, where understanding who is acting "for themselves" and who is simply landscape is crucial for cooperation or defense.

This cognitive predisposition was later formalized in the great philosophical visions: Aristotle spoke of ψυχή as an internal principle of motion and perception, and the Neoplatonists saw life as participation in a universal soul. Seventeenth-century Cartesian thought, however, clearly separated mind and body, interpreting the latter as a mechanical automaton devoid of any intrinsic life principle; in reaction to this model, between the eighteenth and nineteenth centuries, vitalism emerged, which held that corporeal matter should be supplemented by a "breath" or vital force irreducible to mechanical laws. The two visions thus found themselves in open opposition: on the one hand, the mechanistic explanation of physiological and behavioral processes as pure movement of organs and fluids; on the other, the idea that no machine could ever exhibit the cohesion, purpose, and dynamism inherent in living organisms.

It was only with the birth of molecular biology and the deciphering of the genetic code that the notion of "vital force" was definitively set aside, making way for chemical-physical processes describable with precise formulas. However, this victory of molecular mechanics has not eliminated our urge to group complex functions under the label "life": we continue to invest categories such as organism, individual, and even ecosystem with meaning, even knowing that these are functional abstractions born for descriptive convenience. With the advent of studies on complex systems and emergent properties, attempts have been made to transcend the simple distinction between mechanical process and vitalism, introducing quantitative metrics drawn from studies of self-organization, complex systems theory, and non-equilibrium thermodynamics, as well as Maturana and Varela's criteria of autopoiesis. These theories seek to measure the autonomy and internal integration of a system, but end up reproducing the same basic evolutionary mechanism: recognizing in an entity that minimum level of cohesion and intentionality that reassures us of its "similarity" to us. Today, autonomous robotics and generative AI are pushing the threshold of what we define as an intentional agent even higher, while animist and posthumanist approaches remind us that every life–nonlife boundary is culturally constructed and historically variable.

Ultimately, "life" does not exist as a separate ontological entity, but as a dynamic continuum of complex organization, processes, and relationships. Each new metric of "similarity"—be it metabolic functions, adaptive learning capacity, or degrees of informational integration—unwittingly raises or lowers that threshold, demonstrating that the threshold for defining a system as living is a shifting parameter, shaped both by our conceptual categories and by the degree of similarity we choose to recognize in others. The need to establish that threshold as objectively as possible is not merely an epistemic problem, but the reverberation of an ancient evolutionary strategy: determining which, among the many objects we perceive in the world, deserves our recognition as a living agent, capable of intentions and complex interactions with us. Life, then, is a property we feel the need to attribute (and therefore define) because the ability to exercise this attribution has conferred a specific evolutionary advantage both to our species and to many others that distinguish at least some living organisms from the inanimate world, drawing the same advantages from them. But at this point, it's worth asking whether there might not be other constraints derived from our biology that have guided the way we classify living from nonliving.

To this end, we can examine a revealing point: regardless of our culture and society, we tend to rank living things on a different scale of value according to an anthropocentric principle, which privileges animals among living things, and among these, those capable of social and emotional exchange with us, to the point of identifying them as bearers of rights in some Western societies. The imprint of our biology as a social species is evident in this case: the more an organism is able to emotionally connect with us, that is, to ideally become part of our social group, the more we attribute value to that organism, regardless of its practical utility to us. We are not the only ones (since ancient Egypt) who become attached to cats, nor do we bond only with animals that, like them, are useful because, for example, they catch mice: talking parrots, monkeys or piglets raised as children in some remote tribes, pets of all kinds are present in all sorts of cultures and in different eras, all characterized by the ability to establish strong emotional and communicative bonds with the humans who care for them.

The lives of these animals, and by extension of individuals of their species, end up more or less consciously taking on greater value in our eyes: the reason we deem them worthy of greater protection is not because they suffer when mistreated, as is often said, but because they are able to channel our empathy better than other animals who equally suffer when mistreated but are unable to effectively communicate their suffering and thus trigger the kind of emotional responses that are essential to maintaining human social groups cohesive—responses based precisely on empathy. Moreover, dogs, cats, and other animals have adapted to increasingly exploit these types of responses; and our need to recognize a greater value in the lives of these animals, which, as I said, does not reside in their practical utility, is revealing of the very way we have shaped our concept of living things first and then of the scale of living things, placing pigs, for example, much further outside of "ours" than cats (even though there is no objective metric that can justify this emotional distance).

The need to identify and distinguish agents underlies our desire to identify what life is, and our social nature —also exploited by the evolution of certain domestic species—has driven us to create a scale of importance that, although disavowed by modern science, is the one we still apply when we kill a fly and feed a dog, and is the same one we codify in religion and law.

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