Introduction and Objectives

Biology considers various evolutionary patterns, but biology involves life at every level. In biology, life comes from life. However, it is believed that life is the result of the chemical evolution, in which abiotic matter transitioned to biotic. This is the central theme of our paper.

In this article we address selected important milestones of chemical evolution that led to life (e.g. Mason 1991; Brack 1998; Schopf 2002; Hazen 2005). The first such milestone could be achieved by Oparin’s model, which accounts for the early stages of chemical evolution (Oparin 1924, 1968, 1969). These occurred at the dawn of development of primitive chemical systems that were pre-RNA. Oparin’s model consists of spontaneous formation of coacervates that encapsulate chemical matter, undergo primitive self-replication, and provide a pathway to a primitive metabolism. We review the experimental updates of his model from our laboratory (Kolb et al. 2012) and discuss types of selection that could have occurred in these primitive systems. Another major milestone in chemical evolution is the transition from abiotic to biotic. This has presumably occurred later, after the RNA world evolved, together with a more sophisticated metabolism, notably characterized by a chiral selection (e.g. Schopf 2002; Hazen 2005). A controversy of what life is interferes with the efforts to elucidate this transition. Thus, we present various definitions of life, some of which specifically include the requirements and mechanisms for this transition (e.g. Popa 2004, 2010, 2012, 2015; Pályi et al. 2002; Trifonov 2011; Szostak 2012; Koonin 2012). Self-replication is one of the major requirements for life. In this context we re-examine the question if viruses, which do not have capability to self-replicate, are alive (Villarreal 2004; Kolb 2007, 2010; Liesch and Kolb 2007; Kolb and Liesch 2008). This is important especially because of the role of viruses in the origin and evolution of life (e.g. Jalasvuori and Bamford 2015; Villarreal 2015, and the references therein). We draw on philosophy of Hegel, Aristotle, Rescher, Priest, and Fry to guide us in our endeavors. Specifically, we apply Hegel’s law on quantity-to-quality transition (Hegel 1975; Engels 1960) to abiotic-to-biotic transition (Kolb 2005), Aristotle’s philosophy to definitions of life (Kolb 2007), Priest’s dialetheism (Priest 1995) to the question if viruses are alive or not (Kolb 2010), Fry’s philosophy to the beginning of natural selection in chemical evolution (Fry 2011), and Rescher’s philosophy (Rescher 1999) to the possible cognitive bias for simple definitions of life.

Chemical Origins of Life: Oparin’s Model for Primitive Self-Replication and Our Update of His Model

Oparin has proposed in 1924, thus almost 100 years ago, a chemical model of so-called coacervates, which have the ability to spontaneously form primitive cell-like structures, encapsulate chemical matter, undergo primitive self-replication, and provide a chemical pathway to a primitive metabolism (Oparin 1924). He and his co-workers have developed the coacervate model and have performed various experiments to support it (Oparin 1924, 1967, 1968, 1969, 1994; Oparin and Gladilin 1980; Gladilin et al. 1978; Evreinova et al. 1973, 1974, 1975, 1977).

Coacervates are made of aqueous colloidal macromolecular species. They are initially composed of droplets, which upon standing separate into two layers. These are the colloid-rich layer, so-called coacervate, and the colloid-poor layer, known as the equilibrium liquid or supernatant. The two layers, both of which are aqueous, are immiscible (Coacervate, Wikipedia; Menger and Sykes 1998).

Typical macromolecular components of Oparin’s coacervates are gelatin (a mixture of peptides and proteins) and gum Arabic (a mixture of mostly polysaccharides). The coacervate droplets made from these materials resemble amoebas in their appearance, when visualized under microscope. These droplets change shape, form “vacuoles”, release the “vacuole contents”, flow, merge, and divide, as some examples of life-like properties. They form a boundary with the aqueous environment, a cell-like property, and thus may be used as models for proto-cells. At the time of Oparin’s proposal the DNA has not been discovered yet and life was thought to be protein based. Among the most studied features of coacervates is their ability to grow and to mimic self-reproduction, by splitting into “daughter cells”.

Oparin proposed that coacervates have the ability to absorb from the outside small organic molecules that could react inside the coacervates. Such reactions could be catalyzed by larger protein-like molecules which could act as primitive enzymes. These molecules could also be absorbed from the environment. Coacervates which are able to utilize the organic materials from the environment more efficiently than others would grow faster. Eventually they would reach a size which would render them thermodynamically unstable, and they would split into “daughter cells”. Coacervates with the potential to grow would replicate more often. A primitive selection would then be established, which would favor such coacervates.

Eventually, the fast growing and replicating coacervates would exhaust the food supply, namely chemicals from a particular niche of the prebiotic soup. This would set another level of primitive selection. Only those coacervates which would develop chemical pathways to make the food themselves would survive. This process would result in a primitive metabolism.

Self-replication of coacervates ensures that the entire chemical system within the coacervate is transmitted to the daughter cells. This provides a way to preserve chemical composition of the coacervate. However, such a way is inferior to that which is governed by a genetic system.

Oparin believed that the “biological law” of natural selection began to operate when the organic material in the environment became exhausted and the system acquired primitive metabolism that was characterized by the internally organized enzymatic activity (Fry 2000). For Oparin, the first life was therefore protein-based. Oparin wrote his major work on the origin of life when “genes” as bearers of hereditary material were still theoretical concepts. When the genetic system was discovered in 1953, Oparin also acknowledged its role in the origin-of-life theory. Still, he believed that that a metabolic system is a necessary condition for the development of nucleic acids and the genetic code. Thus, Oparin started the “protein-first” view, which is in contrast with later-developed gene-first theories introduced by scholars such as Gilbert (1986), Joyce and Orgel (2006), among others (listed in e.g. Brack 1998; Fry 2000; Schopf 2002; Hazen 2005). Today, the genetic system is a key to all known life forms. How such a system evolved from the primitive metabolism of Oparin is not known.

Many scholars (Fox and Dose 1977; Margulis and Fester 1991, Kauffman 1986, 1993) have argued that if such a “protein first” phase of life existed, it was exempt from natural selection. A recent advocate is Iris Fry, who in her paper “The role of natural selection in the origins of life” specifically addressed Oparin’s coacervates and has proposed that natural selection did not occur before the appearance of RNA polymers (Fry 2011). One can visualize an early chemical selection in Oparin’s coacervates, as described above, before the genetic system became part of it. Only in a later stage/transition of evolution, when coacervates acquired a genetic system, would these coacervates become a subject to Darwinian natural selection. It is not clear that such advanced systems would still need to be coacervates, since a different mode of replication could be implemented. Also, while coacervates provide a natural boundary with their aqueous surroundings, other ways of separating chemical systems, such as primitive membranes, may have been implemented by then. It should be pointed out that the applicability of Darwinian principles to early prebiotic evolution, before the genetic systems, has not been resolved (Perry and Kolb 2004). In this paper we use the term “early chemical selection” in Oparin’s coacervates as opposed to Darwinian selection, since most people believe that the latter started with the appearance of the RNA polymers (e.g. Fry 2011).

Our interest in Oparin’s model is to the extent that we can test some of its features experimentally. Since prebiotic chemistry has substantially advanced since Oparin’s time, we have recently performed experiments that test his model against such advancements (Kolb et al. 2012).

As we stated earlier Oparin’s coacervates are composed from gelatin, a mixture of peptides and proteins, and gum Arabic, a mixture of mostly polysaccharides. The protein/peptide part is prebiotically possible if substituted by protenoids. The latter can be plausibly made by a thermal condensation of prebiotic amino acids (Fox and Harada 1958; Fox 1964), among other means. Prebiotic amino acids would be available on early Earth either by delivery by meteorites of by synthesis via Miller’s experiments (Miller 1953). In contrast, polysaccharides, which are a necessary component of Oparin’s coacervates, are not prebiotically feasible, since they have not been found on meteorites and cannot be prepared experimentally under the simulated prebiotic conditions.

We thus proposed a different coacervate, as one of many possible examples that are prebiotically feasible. Our coacervate is based on AOT, which structure and chemical names are given in Fig. 1. The AOT molecule has functional groups and chemical bonds that have ample precedent in prebiotic chemistry. AOT coacervates have been studied extensively for purpose of learning about the basic science of coacervates, notably by Menger and his research group (Menger and Sykes 1998; Menger et al. 2000; Menger 2002, 2011). These literature resources provided us with a well-tested preparation of AOT coacervate and a detailed knowledge of coacervate properties and behavior. The details of our study are published elsewhere (Kolb et al. 2012).

Fig. 1
figure 1

Structure of AOT, dioctyl sodium sulfosuccinate

Full size image

For comparison, we have also made Oparin’s coacervates, based on preparation by Flammer (http://www.indiana.edu/~ensiweb/lessons/coacerv.html).

At this point we had both types of coacervates available. In the next step we tested if these coacervates can serve as chemical reactors, which is a central part of the Oparin’s model. For this purpose we have chosen a prebiotically feasible multicomponent Passerini reaction. This reaction occurs in water and gives a product in a form of a white precipitate. The reaction occurs fast at room temperature and gives a quantitative yield (Hooper and DeBoef 2009). We were able to demonstrate that the reaction occurred inside coacervates by the visualization of the white precipitate, followed by its removal, chemical analysis and identification.

The reaction scheme for the Passerini reaction is shown, in Fig. 2, together with the chemical names of the starting materials and product.

Fig. 2
figure 2

The aqueous Passerini reaction which was performed inside the AOT and Oparin’s coacervates (Kolb et al. 2012)

Full size image

The Passerini reaction occurred in both types of coacervates. In Fig. 3 we show the photographs of the AOT coacervate which we have prepared in a form of two layers (rather than the droplets) and the AOT coacervate with the white product inside. The Oparin’s coacervates with or without the product look similar, except that they are colored due to the addition of mold inhibitor, which is necessary to preserve the coacervates.

Fig. 3
figure 3

Left photograph of AOT coacervate (the coacervate layer is on the bottom and the equilibrium layer is on the top). Right photograph of the same coacervate with the white product from the Passerini reaction inside

Full size image

Thus, with some updates based on the recent developments in prebiotic chemistry, Oparin’s coacervates represent a likely step and an important milestone in chemical evolution towards life. We conclude that Oparin’s coacervate model surpasses its historic value.

Another major milestone in chemical evolution is the transition from abiotic to biotic. It is believed to have occurred much later than the Oparin’s milestone, only after the RNA world evolved, together with a more sophisticated metabolism, notably characterized by a chiral selection (e.g. Schopf 2002; Hazen 2005). A controversy of what life is interferes with the efforts to elucidate this transition. We thus address definitions of life in the next section. Some such definitions include the ideas about the mechanism for abiotic to biotic transition.

Definitions of Life

Numerous definitions of life, some of which specifically include the requirements and mechanisms for abiotic-to-biotic transition are published in the literature (e.g. Popa 2004, 2010, 2012, 2015; Pályi et al. 2002; Trifonov 2011; Szostak 2012; Koonin 2012). No definition is accepted universally. One rather prominent philosophical view is that life cannot be defined, since we do not understand it sufficiently to allow for a definition (Cleland and Chyba 2002). Another prominent view is presented by NASA in its working definition of life, which extends Darwinian evolution to chemical systems: “Life is a self-sustained chemical system capable of undergoing Darwinian evolution” (Joyce 1994, 2002 as cited in Popa 2004). We have reviewed various aspects of possible applicability of Darwinian principles to chemical evolution that led to life (Perry and Kolb 2004). A lively discussion of definitions of life continues, with new ideas, definitions, and interpretations (e.g. Trifonov 2011; Popa 2012; Szostak 2012; Koonin 2012).

Philosophical approaches are important in search for a universal definition of life. Thus, holism (or generalism) is considered as opposed to reductionism (or minimalism), dialectical materialism as opposed to vitalism (Popa 2010), and also probability (or chance) as opposed to causality (or determinism) (Popa 2015). Holism (or generalism) considers life to be a collective property, and thus is not present in its individual parts. To illustrate this view Popa cites Olomucki: “Nothing is alive in a cell except the whole of it” (Olomucki 1993, as cited by Popa 2015). In contrast, reductionism (or minimalism) attempts to explain life from properties and interactions of its individual parts. Dialectic materialism believes that life is the inevitable result of the evolution of matter, and that such evolution is a subject to Hegel’s laws of logic (Hegel 1975), as applied to matter (Engels 1960). These laws are: the law of the transformation of quantity-to-quality and vice versa, the law of the interpenetration of opposites, and the law of the negation of the negation. Progress of matter towards life is guaranteed by these laws via Hegel’s triad, consisting of thesis, antithesis and synthesis (Engels 1960). Vitalism is the medieval belief that life is caused by an esoteric force, called a vital force, which is beyond comprehension (Popa 2015). It was revived in 1907 by Bergson’s book “Creative Evolution” in which he introduced “élan vital” (vital impulse) as an original common impulse which explains the creation of all living species (Bergson 1998). Popa (2015) points out that modern science has not completely eliminated vitalism. Instead, it may have rephrased the terms vitalism and élan vital so that they sound more rational, but still may not able to explain the new terms fully. We cite Popa’s example: “…scientists now propose that causality (in various forms such as physical driving forces, cause-effect deterministic relationship and derived properties) was important for the origin of life”. Probability (or chance) views life as the outcome of random chance circumstances, such as rare but plausible set of environmental conditions which are conducive to rare chemical events. Causality (or determinism) is a view that life is due to underlying causes, which are more important than chance. An interesting angle on determinism versus chance is taken by Prigogine (Prigogine and Stengers 1984; Prigogine 1997). He investigated complex systems that exchange matter and energy with their environment. Such complex systems go through periods of stability and predictability. However, these periods are interrupted by chance events of bifurcation. The latter are caused by the presence of fluctuating subsystems, in which a single fluctuation or a combination of fluctuations can become very strong as a result of a positive feedback. Such fluctuations force the system into a far-from-equilibrium condition and threaten its structure. They cause a “bifurcation point” in which the system takes a new direction. The latter is not predictable in advance. The system may disintegrate into chaos. Alternatively, it may give a new order or organization, termed “dissipative structures”. Such structures require more energy to sustain them, as compared to the simpler structures they replace. Once the new path is taken, determinism takes over, until the fluctuations force the next bifurcation point. These processes can be applied to abiotic-to-biotic transition (e.g. Perry and Kolb 2004; Kolb 2012).

Popa (2015) analyzes various definitions of life and concludes “…we do not define life, we describe it; we do not accept a definition of life, we understand it; and we are not told what life is, we are taught about it”.

We present in Table 1 a small number of selected definitions of life, in no particular order, just to illustrate a variety of views. These definitions are taken from Popa’s book (2004), which has many more definitions, listed in chronological order.

Table 1 Selected definitions of life, as cited by Popa (2004)
Full size table

The last definition in Table 1 is ours. It explains the emergence of life from the abiotic chemical system, by a Hegelian quantity-to-quality transition (Hegel 1975) as applied to matter (Engels 1960; Kolb 2005). We provide a brief summary of this view.

Both Hegel and Engels were very knowledgeable in chemistry. It is now recognized that Hegel’s chemical knowledge has helped him in formulation of his logic. Engels applied Hegel’s laws to matter. A brief example from Engels illustrates a quantity-to-quality transition in chemistry. A combination of three atoms of oxygen gives ozone, which does not resemble oxygen in its quality. Although we now understand the chemical process involved, and are able to actually predict its outcome, there are more examples of quantity to quality transitions that we are still not able to explain. We have suggested that one of the universal features of the quantity-to-quality change is the organization of the system, which brings about novelty. In the ozone example it would be the change in the spatial arrangements of the atomic nuclei involved, and the new configurations of electrons. We could similarly explain all other examples given by Engels (formation of oxide of nitrogen called laughing gas by combination of oxygen and nitrogen, etc.) as well as many chemical examples that we could come up with today. Based on such chemical examples, one can hypothesize that at the advanced stages of chemical evolution, when primordial soup was rich with complex chemicals, life emerged as a new quality which is characterized by its novel organization. The problem at this time is that our ability to predict the outcome of the law of the quantity-to-quality transition is limited to much simpler examples, which may draw criticism that we actually do not know if such law is universal or not.

Trifonov (2011) sought a minimalistic definition of life. He analyzed the vocabulary of 123 definitions of life with the objective of finding the most frequently used terms. Such terms, he hoped, would reflect the most important points that are shared among the definitions. Trifonov also considered that a minimalistic definition could be the most general one, and thus would apply to any form of life, including the putative extraterrestrial life. Trifonov came up with the definition of only two terms:

“Life is self-reproduction with variations”, and understood this as Darwinian because it involves variations.

This came very close to Oparin’s definition: “Any system capable of replication and mutation is alive”.

Trifonon’s paper drew lively and interesting responses (e.g. Popa 2012; Szostak 2012; Koonin 2012), some of which we describe below.

Szostak (2012) comments: “Attempts to define life are irrelevant to scientific efforts to understand the origins of life. Why is this? Simply put, the study of the ‘origin of life’ is an effort to understand the transition from chemistry to biology”.

Szostak further comments that the attempts to define life are usually biased by the research focus of the scientist. Thus, chemists, physicists and biologists often draw different lines between life and non-life.

Koonin’s response is different: “In my view, although life definitions are metaphysical rather than strictly scientific propositions, they are far from being pointless and have potential to yield genuine biological insights” (Koonin 2012). Koonin states that a necessary condition for life to evolve is “replication with an error rate below the sustainability threshold”.

We now present an argument against seeking minimalistic definitions of life, followed by some additional ideas about definitions of life. These come from our paper “On the applicability of the Aristotelian principles to the definition of life” (Kolb 2005). We give a brief summary of points relevant here. First, we have described the problems with the definitions of life that are too basic. Most definitions of life try to capture the essentials of life that are applicable to all living organisms. Such an approach, by necessity, considers only the lowest common denominator of life. Thus, we would not be able to adequately describe higher organisms using only criteria by which we describe bacteria. This point argues against approach by Trifonov. We also addressed two ways of defining life, as a phenomenon and as a set of characteristics of an individual. Life as a phenomenon is often associated with the population of its entities, and not with an individual. In Table 1 we cite definition of life by Maynard-Smith (1975), which makes this explicit: “We regard as alive any population of entities which has the properties of multiplication, heredity and variation”. We focused on defining life via a set of characteristics of an individual, mostly to bring up the point that an individual may be alive without reproducing. As a follow up of this list of characteristics, we sought inspiration from Aristotle. He may have been the first thinker to consider a living thing by reference to a list of characteristic “life-functions”. Although the list varies in his texts, it usually has a selection from the following: self-nutrition, growth, decay, reproduction, appetite, sensation or perception, self-motion, and thinking. Aristotle also developed classification of existing things, in which he placed an individual living organism higher in the classification than its species or genera. He stated that the individual substance does not lose its qualities when it becomes part of a species or genera, but that the opposite is not true. Thus, the manhood, which would be a generic description of the properties of all men in the species, is not contained in an individual man. General is not present in specific, and abstract is not present in the real. Thus, Aristotle attached a special importance to an individual, whom he considered a primary substance. We believe that this view needs to be considered in defining life via a set of characteristics, as it cautions us against seeking the “essence” of life which would be in common to all living beings since this may not be the case even for the living beings within a species. This again argues against basic, minimalistic definitions. Aristotle’s views imply that an individual man is a real, observable biological entity, while “species” or “genus” are abstract concepts that have merit on a theoretical level. The question if species are real persisted until about 1930s, when the movement which established that species are indeed real started (e.g. Eldredge 1999). As one example relevant to this discussion, species may also be considered as real biological individuals because they are bounded in space and time and have a beginning, lifespan and ending, that can become documented.

The definitions of life that we have cited illustrate disparate views on this subject and do not offer much hope that the matter will settle any time soon. Popa (2010, 2012) expressed this view: “We may never agree on a definition of life, which will remain forever subject to a personal perspective: The measure of one’s scientific maturity may actually be his/her latest definition of life and the acceptance that it cannot be ultimate”.

It is striking that most definitions of life, the ones that we have cited, but many other as well, attempt to define life, a complex phenomenon, in as few words as possible and in as simple ways as possible. Why is that? This discrepancy may be due to the possible epistemic bias towards simple explanations (Rescher 1999).

In his book “The Limits of Science”, in a section “The Principle of Least Effort and the Methodological Status of Simplicity Preference in Science”, Rescher brings up a general problem that scientist have, namely an inclination to choose simple explanations over the complex ones (Rescher 1999). Rescher describes how scientists try the simplest explanations first, and maintain their cognitive commitments to them until there is a good reason to abandon them. Rescher further states how scientists prefer simple explanations because they are operationally more advantageous and they avoid unnecessary complications. Scientists prefer simplicity because it requires less cognitive labor. Thus, principle of simplicity, such as that of Occam’s Razor, is just a principle of managing complexity by economy of rational effort. We cite Rescher: scientists “opt for simplicity …in inquiry not because it is truth-indicative, but because it is teleologically more effective in conducing to the efficient realization of the goals of inquiry”.

We also see a tension between the desire for simple, linear descriptions and the reality of non-linear processes that characterize life. Attempts to describe non-linear processes by linear means ultimately prove to be inadequate and often lead to dead ends.

At the Boundaries of Life: Are Viruses alive?

In our paper “On the applicability of the Aristotelian principles to the definition of life” (Kolb 2007), we summarize the argument that self-reproduction as a criterion of life is problematic. Based on this criterion, sterile organisms, such as mule, worker ants, or organisms at the non-reproductive stages of their development, such as babies or old people, would not be considered alive. This is clearly not the case. Many more similar or related examples exist. Still, the most commonly accepted definitions of life include the requirement for self-replication, and also exclude viruses from the sphere of life, since they can reproduce only in host cells, by utilizing the host cell’s metabolic apparatus. This sort of reproduction could be considered as an assisted reproduction, and various other species use it. However, viruses are consistently singled out, based on their relatively simple structure.

In this section we address a question if viruses are alive, in conjunction with selected philosophical approaches.

The question if viruses are alive was discussed by Villarreal (2004), who proposed that viruses are in the twilight of the life zone. We have also addressed this question in our paper “Abiotic, biotic, and in-between” (Liesch and Kolb 2007), and also when considering viruses as life forms (Kolb and Liesch 2008). In these and numerous other sources it is stated that viruses are not considered alive by the criterion of their lack of the ability for self-replication, since they depend on their host for replication. However, an argument was given that viruses undergo assisted reproduction, namely reproduction with the help of the host, and thus could be considered alive. Role of viruses in the origins and evolution of life has been recognized (e.g. Jalasvuori and Bamford 2015; Villarreal 2015), and thus the question if viruses are alive or not is definitely very important.

We have addressed the question if viruses are alive in a more philosophically-oriented paper, on dialetheism (Kolb 2010). Here we give a summary.

Dialetheism is a branch of philosophy which was proposed and is practiced by Priest (1995, 2006). According to dialetheism, some contradictions may be true, typically at the limits of a system and during the transitions. It should be noted that dialetheism does not apply to any statement and its negation.

Dialetheism departs from the Aristotelian logic, in which a statement may be only true or false. Instead, dialetheism states that both statement and its negation could be true. The name dialetheism reflects this belief. It comes from Greek: aletheia = truth, and di-aletheia = a two-way truth. Priest gives a simple example of a dialetheism, by considering a person exiting the room through the door to go outside. As the person is passing through the open door, the person will be both inside and outside the room at some point of this transition.

We have applied dialetheism to answer the question if viruses are alive or not. Viruses may be considered not alive based on the criterion that they cannot reproduce on their own. The form of viruses which is non-reproducing would be their virion phase. However, when virions penetrate their host, they become capable of reproducing by making use of their host’s metabolism to make more viral copies. They would then be considered alive because they reproduce. Viruses thus can be considered both alive and not alive. While this would not be allowed by the Aristotelian logic, it is allowed by dialetheism. Viruses are clearly at the limits of life, when such contradictions are allowed. This reasoning is related to epistemological pluralism in philosophy of science, which expresses the view that at least some natural phenomena cannot be fully explained by a single theory or fully investigated using a single approach (e.g. Kellert et al. 2006). This is especially true for evolution for which the practice of epistemological pluralism is quite fruitful (Gontier 2012).

We bring up the need to apply philosophy of identity to the definition of life (Kolb 2010), this time to the virus reproduction. Let us consider another way of viral reproduction, the lysogenic stage (Carter and Saunders 2013). In this case virus gets incorporated into the host’ genome, it passively reproduces when the host reproduces, and thus gets incorporated into the daughter cells. Is this virus alive or not alive? Since it reproduces, although in a passive mode, it could be considered alive, but it has lost its original identity. Its identity in the lysogenic phase is inseparable from that of the host. Thus, one can claim that the virus as such is not alive. However, in the later stages of its residence in the host, the virus may separate from the host’s genome and then go to the lytic stage. This would result in virus gaining identity separate from its host. Such identity would help us relate it to the original virus. The identity dilemma of the virus in the lysogenic stage may be considered in light of Gallois’ occasional identity theory (Gallois 2003; Kolb 2009, 2010). We briefly summarize the identity issue here. The reader is referred to our original paper (Kolb 2010) for a detailed discussion of the identity problem. For each organism its identity will be in relation to itself. An individual organism is numerically the same (it is ‘one’), even though it exists over its life time in various life forms, which are qualitatively different. If the organism reproduces then each offspring would have its own numerical identity. The identity of life may be understood via a spatiotemporal succession of its life forms, which may assume identities which differ and hold only temporarily (occasional identities). Although the life forms change and the organism is in a flux, what remains constant is the numerical identity of the organism. Based on the identity criterion, we could say that virus is alive throughout its life cycle, in its non-reproducing stages and while reproducing, via lytic or lysogenic mode.

Dialetheism can also be applied to the abiotic to biotic transition. Earlier, we have proposed the existence of a transition zone to life (Perry and Kolb 2004) and have visualized the abiotic to biotic transition within it as a Hegelian quantity to quality change (Kolb 2005). However, with the acceptance of dialetheism, we can now describe the matter in the transition zone to life as both alive and not alive (Kolb 2010).

Summary and Conclusions

In this paper we have presented a selection of topics that are important for the chemical origins of life, and have explained how philosophical approaches can be useful in defining life and the abiotic to biotic transition to life. We have selected topics and approaches that appeal to us, which we have studied the most, and which we believe are important and fruitful, and have focused on them. More in-depth coverage of specifics is provided in the references. Our hope is that this overview will be useful to the readers.