“…First, to understand what life is, we must understand how we identify it. Evolutionary psychologists claim that we distinguish living and non-living things only because it confers a genetic advantage. Animals need to know what to count as predator or prey – they cannot afford to waste time running away from rocks. The human tendency to err on the side of caution – the coats in the cupboard become a terrifying monster – is a throwback to our evolutionary heritage when failure to recognize sleeping lions as alive could be fatal. Because of the obvious survival-advantage of life-recognition, psychologist Steven Pinker argues that we possess a ‘folk biology,’ analogous to folk psychology:
“The distinction between living and non-living things is appreciated early, perhaps before the first birthday. The cut originally takes the form of a difference between inanimate objects that move around according to the rules of billiard ball physics and objects like people and animals that are self-propelled.”
Experiments by psychologist Frank Keil demonstrate that toddlers shown a toy bird being covered in real feathers and filled with ‘avian-insides’ always say it is still non-living. Despite lifelike cosmetic changes, it still lacks a critical something to make it a real bird. We can conclude that in the same way that we think of other humans as possessing minds, we think of other living things as possessing some quality which makes them living. This, I believe, is the origin of Haldane’s intuition.
The philosophy of Vitalism values this intuition as the best tool to define life, arguing that every life-form is made living by a something special, an ‘oomph,’ which we cannot reduce to mechanical laws. Haldane himself said: “It is life we are studying in biology, and not phenomena which can be represented by the causal conceptions of physics and chemistry.” Life, being self-propelled, was somehow beyond physics – this idea led philosopher Henri Bergson to posit a new vital-force of life located in the cell cytoplasm. In the early twentieth century, however, cytoplasm was revealed to be governed by the same laws as any chemical – no magical ‘oomph’ was ever found. And no wonder! It is an easy explanation which explains nothing; a hazy tautology – vital-force is the thing that makes living things living – designed simply to justify our intuitions.
Ultimately Haldane came to reject Vitalism, preferring to see life as a multifaceted phenomenon. This appealed to philosopher Henry Woodger who urged scientists to abandon the word life, instead sticking to listing the properties of living organisms. The laboured definition has now become paradigmatic, turning biologists away from the big philosophical questions concerning life. This is seen in the introduction to most biology textbooks.
But the problem with the listing method is that it pretends to tell us what life is, but really only gives us a shopping list of things to look for in living things, ignoring the deeper question of how these properties make things living. Furthermore, lists almost always disagree, being dependent on the author’s personal prejudices. Hiding behind our intuition, Steven Pinker says, is a subjective tick-box of properties which the professional biologist merely couches in technical language. The most important of these properties is the idea that each life-form, besides being self-propelled, contains an essence – a caterpillar may change into a chrysalis, and then into a butterfly, but despite these huge anatomical changes we feel it is still the same animal. Non-living objects lack this essential identity which goes unchanged during the life-cycles of living things.
Taxonomist Ernst Mayr believes that Essentialism is just as dangerous as Vitalism when defining life. He blames Plato’s Perfect Forms and their overbearing influence on Western philosophy. We divide organisms into broad taxonomic categories, specifying the ideal (average!) ant or panda – knowledge we can then use to generalize and make predictions about nature. But therein lies the rub: Mayr says “generalizations in biology are almost invariably of a probabilistic nature.” Science, as a product of our essentialist intuitions, has been dominated by the search for strict definitions and universal laws. When defining life, however, we must embrace what Mayr calls ‘population thinking.’ We must see each individual in the population as unique, rejecting the idea of the typical tiger.
Because “variation is attributed to the imperfect manifestation of the underlying essences,” many intuitive essentialists struggle to accept evolution by natural selection. Consider the creationists’ mocking demands for a ‘fronkey’, halfway between frog and monkey – they see species as inviolate categories. They imagine evolutionary change as being a Pokémon-like transformation from the essential-Frog to the essential-Monkey. But all life-forms are perfectly capable of breeding with their children, and with their grandchildren – they are ‘essentially’ the same animal. Once we increase the genetic distance to the thousands of generations, however, life-forms diverge, and become ‘essentially’ different. Nevertheless, neo-Darwinism necessitates that there can be no moment when one species turns into another. Species are nothing more than convenient spatial categories which divide reproductively-isolated populations, descended from a common ancestor.
So if our sharp essentialistic categories are mistaken, why not the jagged vitalistic dichotomy which splits living from non-living? When ethologist Richard Dawkins popularizes evolution as a River Out of Eden – Eden being the beginning, or origin, of life – we must extend the metaphor and ask where does the river begin? A river’s source can be an underground spring. Yet the source of the spring is the water table, the source of the water-table is seeping water, whose source in turn is snow, and so on ad infinitum. A geographer could define any of these points as the source, yet his definition would ultimately be arbitrary. By the same token, the moment in time when non-living matter became living matter is itself an arbitrary point.
The chemist Manfred Eigen argues in his book Steps Towards Life that the origin of life was instead itself an evolutionary process. The title is telling: he posits no jump from non-living to living, but a gradual evolution from silicate-based molecules to self-replicating carbon crystals and thence to single-celled organisms. The insight is not in the chemical details but in the process described. Pre-biotic molecules, Daniel Dennett says, can be called ‘macros’: “bare, minimal self-reproducing mechanisms.” Basically non-parasitic viruses, they are a phenomenon reducible to chemistry, but which also carry self-replicating information in the form of RNA. Natural selection can operate on that information favouring in the end the development of cell-walls and all the paraphernalia of life: “macros gradually built up [the] ‘molecular toolkit’ that living cells used to recreate themselves, while also building around themselves the sorts of structures that became, in due course, the protective membranes of the first prokaryotic cells.”
This theory – or at least the underlying mechanism – chemists say, is our best plausible explanation of the origin of life. For philosophers investigating life, however, the interesting fact is that evolution by ‘macros’ is purported to have taken almost one billion years. Thus we have a huge temporal fuzzy zone between matter we would definitely call non-living and prokaryotes we would certainly call living. Dennett calls the macros ‘quasi-living’ – but are they 99%, 50% or 20% living? The question is absurd. Yet, if we take Vitalism seriously, we are obliged to ask it – if living things are driven by pure ‘oomph,’ quasi-living things must have some fraction of that ‘oomph!’ The evolutionary model of the origin of life says that there is no exact cut-off from non-living to living, implying that whatever defines life cannot have just appeared; it must have evolved. The consequences of this for our understanding of life are enormous. If we can’t clearly separate living and non-living matter in time, why should we be able to do it in space? This calls for a far looser concept of life, derived from those pre-biotic macros.”