The Daily Ant hosts a weekly series, Philosophy Phridays, in which real philosophers share their thoughts at the intersection of ants and philosophy. This is the twenty-eighth contribution in the series, submitted by Dr. Marc Lange.

Ants Are Alive

Ants are widely reported to be alive. These reports raise an obvious question: What is it for something to be alive?

By this, I do not mean to ask what makes something alive rather than dead. Only a thing that was once alive (or, at least, could have been alive) can be dead. A rock is not dead; it was not ever (and could not ever have been) alive. The question that I am asking is not what distinguishes a living human being from a corpse, when is the moment of death, or is there a moment of death. Rather, the question I am asking is what distinguishes living matter (of which an ant is one example) from non-living matter.

This is an important question for exobiology: the study of life elsewhere in the universe. What are scientists looking for when they are looking for extraterrestrial life? If a future space probe supplies evidence that there is extraterrestrial life somewhere, what will this be evidence for?

As late as the early twentieth century, some scientists believed that living matter is distinguished from non-living matter by what it is made of. According to “vitalism”, living matter contains a vital spark or fluid or some other kind of stuff that is absent from non-living matter. Vitalism was not as outlandish an idea as it might seem to us nowadays. Various subtle fluids were often invoked in nineteenth-century physics, as when heat was regarded as a fluid (caloric) that flows from hotter bodies to cooler ones. Various capacities of living things – e.g., to move, to synthesize various chemical compounds, to reproduce – had not yet been explained in terms of the capacities of ordinary matter. However, the prospect of giving these explanations has since then greatly increased, and as a result, vitalism has become less and less plausible.

Another option is to reject the question of what makes some matter living on the grounds that there is no non-arbitrary place to draw the line between living and non-living matter. Viruses famously seem like living things in some respects but not in others. They are not cellular but they can reproduce — but they cannot reproduce all by themselves. (Nor can I, of course.) They cannot move of their own accord, but some parts of them (such as their injectors) can. They require no nourishment and can essentially last forever if unmolested. Chemical evolution supplies another argument that there is a grey area between life and non-life. If living matter arose from non-living matter, presumably the boundary was not crossed at a particular moment. Rather, matter became increasingly alive.

But even if being living is not an all-or-nothing matter, it can still make sense to ask what it is for something to lie more towards the living end of the spectrum or more toward the non-living end. Even if vitality is a matter of degree, we should try to understand what features contribute toward vitality, placing some matter at some location on the spectrum. Being living or non-living can be like night and day, which also have intermediate stages.

There is another popular option (especially in the boilerplate opening chapters of biology textbooks, which often define biology as “the study of life” and then find themselves facing the uncomfortable question, “What is life?”). It is to go functionalist: some matter is alive to the degree that it can perform various “life functions”, such as reproducing, exchanging energy with its environment, responding to stimuli, organizing the matter that it assimilates into a new form, moving of its own accord, and so on.

Admittedly, many living things do many of these things. But of course, many non-living things do, too. A hurricane takes in matter from its environment and assimilates it into a new form, as does a water wave. They both move. A candle flame “reproduces” (given an unlit candle) and exchanges energy with its environment. A piece of iron responds to the stimulus of being in the presence of oxygen by rusting. The fact that these non-living things possess some of these capacities does not move them even a smidgen toward the living end of the spectrum. Likewise, there are many living things that lack some of these capacities. Yet a sterile “worker” or “soldier” ant is no less alive than its fertile colleagues.

Another problem with functionalism is that there does not seem to be anything that ties the various “life functions” together. They seem to form an arbitrary “laundry list” of capacities that (arguably) are more common among living than non-living things. What is it that makes a given capacity qualify as one of the “life functions”?

Nevertheless, functionalism seems like it might contain some kernel of truth. After all, in a famous Sesame Street sketch, Robin Williams uses functionalist grounds to argue that his shoe is not alive because it cannot eat, breathe, or grow.

Perhaps one step towards understanding what might be correct about functionalism is that the fact that a given thing is alive has sometimes been used to explain why that thing has the capacity to perform a given life function. In the history of science, we can find cases in which scientists explicitly debated whether or not some entity is alive, and the debates focused on whether or not its vitality is the most plausible explanation of some of its capacities. That the heavenly bodies move was once widely believed (even as late as Galileo’s time) to be best explained by their vitality. Likewise, until the mid-nineteenth century, scientists debated whether fungi are alive, and these arguments concerned whether fungi exhibit some “life functions” and, if so, whether the best explanation is that they are living. (It was long unclear, for instance, whether fungi grow, reproduce, or move.)

What would it take for a thing’s vitality to explain why it has various capacities? Perhaps it will turn out that all living things, when they perform their life functions, do so in an importantly similar way that is uncommon among non-living things with these capacities. Of course, this similarity would have to lie at a fairly deep, abstract level. One possibility is that living things perform these functions in a “bottom-up”, “self-organized”, “emergent” way. That is, roughly speaking, although each component (at a fairly basic level) of a living thing is governed by equations that determine its behavior given its environment, there is no such equation for the living thing as a whole. Its final state cannot be computed by some effective procedure, even given its initial state and its surroundings. There are cellular automata (see here) where each component’s next state is determined by a simple rule plus its neighbors’ current states, but where there is no way to predict the overall outcome except by stepping through a simulation of the system.

Perhaps what contributes toward making something living is not merely that it performs a life function, but that it does so emergently. Perhaps what puts a capacity among the life functions is that it can be performed emergently. Perhaps when vitality explains why a living thing can carry out various life functions, the explanation does not supply the precise causal mechanism that the living thing uses, but the explanation nevertheless specifies an important feature of the causal story: that the life function arises emergently.

On the other hand, perhaps there is nothing important that is common to the ways in which living things perform their life functions and that is uncommon among non-living things. Perhaps the notion of vitality is just an outmoded vestige that ultimately has no scientific work to do. Which of these options will prove to be the case is an open empirical question.

Dr. Marc Lange is the Theda Perdue Distinguished Professor at the University of North Carolina at Chapel Hill, as well as Chair of the UNC Department of Philosophy. Dr. Lange specialized in philosophy of science, metaphysics, and epistemology – check out his description of his own extensive work, in a display of extraordinary adjective diversity, here.