The Nature, Origin, and Evolution of Life: Part V Bringing It Together: Concepts, Constraints, and Closure

“An organized being the, has the property that the parts exist for and by means of the whole” - Immanuel Kant

“Life spirals laboriously upward to higher and even higher levels, paying for every step.”

Ludwig von Bertalanffy

“The nature and origin of coherent, controlled collections of elements remains then a central problem for any theory of life.”

Howard Pattee

Introduction

A common, albeit somewhat elusive, thread has run through previous editorials on conceptualization, language and symbol formation, cognition, consciousness as well as the fundamental nature, organization, development and evolution of life. The common thread, in its varied portrayals and nuances, has been the unavoidable conclusions that the properties of language, cognition, life and indeed, complexity itself, emerge from but cannot be defined, predicted or explained by the underlying physical world of subatomic particles, atoms, molecules, cells etc in hierarchical levels of reality (1–4). In the Kantian view, the composite whole of a functioning, replicating and evolving entity is more than simply the compilation of its component parts. Rather, out of it emerges an new, unexpected, higher-level set of properties emerge and gain meaning at each level within the context of the next higher level and the whole.

Beauty, meaning and all the properties of the world that we consider worthwhile, including life, our social, cultural and historical creations, and the true essence of existence are the product of those unanticipated wholistic properties of our world. What is needed for life, language, consciousness and all of these properties to emerge are constraints on the underlying dynamics including a controlled and directed flow of energy and collective closure or completeness of the underlying elements needed to sustain the whole and provide function or purpose within the whole. The function or meaning of any part emerges only because of its essential role within the functioning meaningful whole.

Functional hierarchies and controls in living matter

As Pattee has elegantly highlighted, finite sets of functional constraints are a fundamental property of all hierarchies and necessary for all languages in the broadest sense (2,5). As he has noted, time-dependent function is an essential characteristics of hierarchical organization of living systems, and requires variable or time dependent constraints on the individual elements imposed by a collective integrated system (5). As an example, he notes that an enzyme is a time-dependent constraint for a substrate which controls the collective interaction of many atoms so as to speed up the formation of a strong bond” (6).

Fundamentally, simplicity of collective integrated function emerges from more detailed complexity when an observer or a measuring device such as an enzyme imposes function resulting in an alternative description or record of the system’s elementary details. As Pattee also notes, the alternative description of the underlying details results from the classification of variables at the most detailed level resulting in fewer variables at the higher level (5). This requires rules or constraints for the simplification of the underlying details to form an upper level record or alternative description of those underlying details. Some of the system’s degrees of freedom must be constrained or ignored to impose collective and time-dependent behavior.

The fundamental physical requirement for all hierarchies, including languages, are fixed and finite sets of arbitrary, conditional (time-dependent) constraints. Life requires autonomous hierarchical constraints representing rules arising within and out of a collection of elements and influencing the individual elements. The collective constraints affecting individual elements always produce some integrated function or purpose within the collection. New constraints emerge within an aggregate of cells in the form of a message or information that modifies gene expression controlling the behavior of individual cells. Such hierarchical control results in some form of organized behavior or function within the whole system. Therefore, a coherent set of hierarchical constraints represents a language structure or grammar that enables a symbol or message read or understood by a measuring device or observer.

As noted by Pattee (5), properties of control hierarchies include 1) a collection of elements that obey the fundamental laws of physics while constraining behavior of elements of a collection to perform some coherent activity or function. Forces of constraint are not the detailed forces between individual particles but forces resulting from collective coherent action of particles; 2) The coherent activity of the hierarchical control system is simpler than the detailed activities of its elements implying that some detail is selectively lost in the operation of the constraint (the measurement or observation) when the constraint selects which details of the elements are relevant resulting in a new simplified higher level description; 3) Hierarchical constraints determine which dynamical details are ignored by a process of classification based on some physical change. The resulting alternative description or record demonstrates that some rule of classification of the elements has been applied as when an enzyme recognizes a substrate. 4) Both the selection of relevant or sensitive degrees of freedom and the mechanism which performs the selective activity appear largely arbitrary. Arbitrary but definite constraints correlate structure with an operation and represent the fundamental property distinguishing symbolic aspects of events with the actual physical event. 5) New hierarchical constraints can continue to appear at yet higher levels without destroying the existing constraints at the lower levels. 6) There are many physical structures that execute the same function and many descriptions of the same physical structure, e.g., the same enzymatic function can be achieved through equivalent structures.

Life represents an elegant example of a multilayer hierarchy resulting from a set of autonomous constraints represented by internal coherent or integrated functional behavior of the underlying particles/atoms/molecules/cells/organismic details. The living substance can thus be thought of as a higher-level alternative description of the underlying dynamical details resulting from the internal coherent behavior of an arbitrary set of functional constraints that fulfill conditions of a living language.

Basic properties of language and living control Hierarchies (5)

Like language, control hierarchies can be described physically as coherent collections of constraints limiting the freedom of individual elements of the collection. Living control hierarchies must also have evolutionary potential establishing new levels of function and control changing continuously without, at any point, losing grammatical structure which defines the meaning or consequences of its descriptions (5).

In summary, living control hierarchies require that a collective group of elements performs some coherent activity or function which is simpler than the underlying elements through classification or ignoring of some of the dynamical detail within the system according to arbitrary but fixed distinguishing rules or constraints that select which degrees of freedom are effective in the operation of the constraints (5). Following classification there must be a record or alternative description (symbolic representation) to show the rule has been applied. A coherent set of constraints (integrated and functional) must exist within the system. In conclusion, life and language are parallel and inseparable concepts. The evolution of the many hierarchical levels uniquely characteristic of living organisms depends on corresponding levels of alternative descriptions operating within a living language system.

Constraint closure, work cycles and autocatalytic tasks

Despite decades of research and speculation on the nature and possible origin of life, a cohesive and comprehensive understanding of how life started and how it increased in complexity has been lacking. Stuart Kauffman has proposed that the missing intellectual and experimental elements may be found in in the concept of ‘constraint closure’ highlighted in recent work of Mael Montevil and Mateo Massio (7,8). The concept of constraint closure, as proposed here relates to how a complex system is capable of creating its own constraints. In living organisms, this requires a set of constraints on the controlled release of energy through thermodynamic work cycles enabling them to reproduce themselves (8).

The construction of constraints discussed previously requires work to be done which, in turn, requires constraints on an energy source. Without a constraint controlling the flow of energy, work is not done, and energy is dissipated as heat and not useful work. In physics, work is considered the product of a force over a specified distance with the assumption that constraints or boundary conditions already exist. However, it is essential to our understanding of work that it requires not only the release of energy but constraints on that energy allowing a controlled release of the energy toward accomplishing a specific action or task. If the energy is released suddenly as in an explosion or heating of a gas in the open without constraints, no work is accomplished. A perfect example, cited by Kauffman, is a steam engine with the heating of a gas within a cylinder which is fixed on all side except a piston that is pushed by the expanding gas. That motion or kinetic energy can then perform work. The constraints channel the release of energy into work. Needless to say, not all energy is perfectly converted into work with heat also released increasing the overall system entropy despite work being done. Entropy still increases but more slowly.

Uniquely, living systems are capable of constructing their own constraints on the release of energy bringing closure to the thermodynamic work cycle. In this setting, the work accomplished is the production of new constraints through an enzyme which constrains the motions of the atoms by forming molecular bonds as in a redox reaction discussed previously (9,10). A set of enzymes that catalyze a complete series of steps in a the closed chain discussed above provides catalytic task closure or a collective autocatalytic set (8,10). These catalyzed steps may involve the formation of peptide bonds linking peptide chains to form proteins for structure or new enzymes for further catalysis enabling various metabolic pathways.

Finally, for life to emerge, an autocatalytic processes is needed whereby each element in a set is capable of catalyzing the development of others with the chain looping back and catalyzing the initial element closing or completing the loop (8). Therefore, the entire set, as a whole, catalyzes itself and all of the catalytic tasks collectively complete the required reactions to sustain the process. Closure, in this setting, is a collective property. Experimental work has demonstrated that, given the necessary conditions and ingredients, autocatalytic sets can arise spontaneously (8).

More generally, for a biological unit to have a function within the whole, it must contribute to and perhaps be essential to the existence and survival of the whole. The unit may do other things or have other effects, but its function is such that the whole depends upon it for producing a specific essential effect. In a living system, the function of a peptide is to catalyze some other peptide as an essential functional part of the whole organism (8). Such functional entities exist above their detailed atomic elements by virtue of their role in the whole living organism. Its function in a collective autocatalytic set is to sustain the functional whole. Kauffman argues that what emerges above the level of the atoms includes new, unforeseen and unpredictable functional entities that come into existence and persist because they enable the existence and survival of the whole.

Theseus’s Paradox

An important but often overlooked corollary to constraints and constraint closure relates to what we might call the identity problem resembling the thought experiment often called Theseus’s Paradox originally formulated by Plutarch and reformulated by Thomas Hobbes (11). The essence of a constraint is not so much the substance (atoms or molecules) constituting the material aspect of a constraint or boundary such as a membrane or enzyme. Rather it is best thought of as the associated force imposing the constraining influence on the underlying dynamics of matter or energy. As Kauffman has pointed out, collectively autocatalytic sets may consist of proteins, DNA, RNA or other polymers with similar constraint properties (12).

Recent studies have demonstrated that the atoms in our body are replaced every 5–10 years and upwards of 98% are replaced every year and yet we consider ourselves the same conscious person and the world around us to be the same world. It goes without saying that if those atoms or molecules were magically replaced by equivalent material objects exerting the same force or by a force field with the same effect, the resulting constraint would be the same even though the ‘material substance’ of the constraint was completely different. As the organism develops and eventually evolves, the wholistic completeness of life’s collectively catalytic constraints must persist without interruption over time even as the atoms and molecules are individually replaced or even improved through natural selection. The continuity of an organism though the developmental process or a species throughout evolution is and must be maintained through the continuity of the relationships and processes needed to maintain constraint, work and catalytic closure even though the physical components may be completely replaced.

While we think of the living substance or organism as a collection of physical entities, it is their functional effects and associated forces that constrain the release of energy and catalytic effects and not the associated substance. This can be and has been illustrated by connected graphs where the physical units are represented by a symbol and the interactions between them by lines representing the effects of forces exerted on these such as catalysis which speeds up reactions (12). When more connections or interactions take place, a rapid escalation in the interconnectedness of the elements of such a system emerges increasing the potential for(catalytic) closure and a sustainable ‘wholeness’ (13).

The emergence of life: When the whole becomes more than the sum of its parts

As we have seen, life requires constraints or boundary conditions, such as membranes and enzymes, on the storage and constrained release of energy such that it can do the work of molecular building and replication. Constraint closure reflects the ability of the constrained release of energy or work to construct a new set of constraints by virtue of a collective set of thermodynamic work tasks resulting in work task closure. When all of this is accomplished through a collectively integrated network of catalytic reactions, catalytic task closure is realized. If such a system is capable of reproduction, it has achieved the functionality of a living system subject to natural selection and evolution. Life requires an integrated and internally complete network of molecules capable of catalysis such that the production of each molecule is catalyzed by one of the other molecules which in turn catalyze other steps. Each molecule is thus catalyzed by one of the other molecules in the system and, in turn, itself catalyzes another molecule. Therefore, “The set as a whole mutually catalyzes the formation of all the members of the set. This property is not present in any single molecule but distributed throughout the set” (8).

The principle takeaway message from all of this is that the functionality of living matter is based on cohesive and collectively complete interactions and processes none of which is alive based on its own merit. Life emerges from the integrated whole where each process is dependent upon and sustains the others. Life exists only by virtue of the whole capable of constructing constraints on the release of energy and the replication of the very constraints as a functional whole.

While the focus of this discussion has been on the origin, development and evolution of life, much of this can be generalized to cognitive, conceptual and symbolic processes including language and consciousness as well as to social and other higher-level groupings of living systems evident within the biosphere. Much like a symbol only has meaning within the larger context of experiences and memories or a word has meaning within the larger context of grammar and a language or perhaps even consciousness exists above the larger context of the entirety of mental (neurons, senses, memories etc) and social (historical, cultural etc) context within which we exist over time, the organism exists and is sustained by the whole of its collectively integrated functional parts.

In the words of Pattee, “The integrated records, descriptions, and instructions in cells are no less a language system because we know the molecular structure of some of their coding devices and symbol vehicles. The full necessity of an authentic language system for the very existence of life is seldom recognized. In biological studies at all levels of organization we find the same implicit recognition of language-constrained behavior, such as references to hormones, chemotactic substances, and controllers of genetic expression as message molecules… However there is almost no discussion of why a particular chemical reaction is regarded as a message or an instruction. All the attention is on the chemical structure of the message vehicle and its interactions with its target, or on the formal, mathematical modeling of this process. What we need to know is how a molecule becomes a message.” (14)

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.