A COMMON DYNAMICAL THREAD.
The fact that there are spontaneous inorganic processes that generate macroscopic order is seen by many as a missing link between living and non-living processes. Even the simplest life forms are remarkably complex in their microphysical structure and chemical dynamics, and all forms of life exhibit the uncanny ability to resist the relentless eroding influence of thermodynamics. So, demonstrating that structural and dynamical regularity can arise spontaneously in the absence of life provides some hope that the life/nonlife threshold could be understood in terms of a special chemical self-organizing (morphodynamic) process.
Indeed, there are many who believe that life is essentially a highly complex form of self-organizing (i.e., morphodynamic) process. The question that will occupy this chapter is whether life is nothing but complex morphodynamics, or whether instead there is something more to life than this, an additional emergent transition. As the t.i.tle of this chapter suggests, I will argue the latter, but like the transition from thermodynamics to morphodynamics, this additional emergent transition turns out to be dynamically supervenient on morphodynamics and therefore also on thermodynamics. Explaining this doubly emergent dynamical logic is not just relevant to life, however. As we will see below, this additional emergent dynamical transition is necessary to account for ententional phenomena in general. Morphodynamical processes generate order, but not representation or functional organization, and they lack any normative (or evaluative) character because there is nothing like a self to benefit or suffer.
I will call this particular way of organizing causal processes teleodynamics, because of the characteristic end-directedness and consequence-organized features of such processes. By describing the emergence of this mode of dynamical organization from the simpler modes of thermodynamic and morphodynamic processes, and its dependency on them, we will build the base foundation upon which the emergence of more highly differentiated forms of ententional relationship can be understood, including even human consciousness.
Evidence that life involves morphodynamic processes comes from two obvious attributes that are characteristic of all organisms. First, organisms are incessantly engaged in processes of creating and maintaining order. Their chemical processes and physical structures are organized so that they generate and maintain themselves by continually producing new appropriately structured and appropriately fitted molecular structures. Second, to accomplish this incessant order generation, they require a nearly constant throughput of energy and materials. They are in this respect dissipative systems. Together, these two characteristics give life its distinctive capacity to persistently and successfully work against the ubiquitous, relentless, incessantly degrading tendency of the second law of thermodynamics. Individual organisms do this via metabolism, development, repair, and immune response. Lineages of organisms do it by reproduction and evolution. In this chapter, I will argue that these are all products of a common dynamical logic.
Though life is characterized by its success at circ.u.mventing the near inevitability of thermodynamic degradation, this does not mean that the global thermodynamic trend is reversed-only that living processes have created protected local domains in which the orthograde increase in entropy is effectively reversed by virtue of contragrade processes that generate order and new structural components at the expense of a net entropy increase in their surroundings. But living processes are not just local pockets of resistance against entropy increase. They also persistently decrease it, within themselves and their progeny over the course of evolution, by developing and evolving complex supportive correlations between structures and processes for maintaining bodies and ecosystems. They do this in the context of specific and often variable environmental conditions. This is the feature of organisms that we describe as adaptation. In terms of thermodynamics, an adaptation can be defined as any feature of an organism or lineage of organisms that directly or indirectly plays a role in compensating for spontaneous entropy increase within organisms. This can be as specific and local as molecular repair and replacement processes within cells, or as general as organism behaviors that compensate for changes in essential resources or critical physical conditions present in the environment.
Without question, the most dramatic expression of the emergent nature of life"s distinctive dynamic is the generation of increasingly diverse and complex forms of organisms that have evolved during the past 3.5 billion years of Earth history and have adapted to an ever-increasing range of environmental conditions. In the general dynamical terminology that we have been using, this evolutionary process must be understood as an orthograde process because of the spontaneity of its dynamical asymmetry. In other words, although evolution depends on the work done by organisms resisting degradation long enough to reproduce, the global asymmetric dynamic of evolution (constantly adapting organisms to changing environments, creating and expanding into novel niches, and producing increasingly complex forms over time) is only an indirect higher-order product of this work. There is no work that forces this particular trend in contrast to the opposite trend, and indeed evolutionary degradation is common. The asymmetry of the evolutionary process is the result of formal asymmetries in the s.p.a.ce of options for adaptation that spontaneously tend to arise over time for living ecosystems. These options (niches) are like the formal features of the s.p.a.ce of opportunities for change that characterize orthograde processes in both homeodynamic and morphodynamic processes. Like the transition from thermodynamics to morphodynamics, the higher-order break in orthograde symmetry exemplified by the evolutionary process is one of the defining characteristics of an emergent dynamical transition.
The thermodynamically exceptional and mechanically counterintuitive reversal of the causal logic of natural selection stands out as one of the most significant dividing lines in natural science. Described in terms of thermodynamics, living processes superficially appear to exhibit mirror-image tendencies compared to what is common in the non-living world. On the non-living side, we find processes that (a) have wide generality in their dynamical tendencies; (b) are describable with good predictive power by fairly simple dynamical equations or statistical methods; (c) exhibit higher-order aggregate properties that can typically be extrapolated from properties of their components in interaction; and (d) exhibit a tendency to dissipate constraints, simplify complex interdependencies, and redistribute free energy in ways that decrease any capacity to do work. On the living side, we find processes that (a) consistently part.i.tion thermodynamic processes so that many component processes follow trajectories that run radically counter to global thermodynamic probabilities; (b) are highly heterogeneous in their structures and dynamics; (c) produce processes/behaviors that are so convoluted, divergent, and idiosyncratic as to defy compact algorithmic description; (d) generate and maintain aggregate systemic properties that are quite distinct from properties of any component; and (e) reflect the effects of deep historical contingencies that may no longer be existent in their present context.
The transition from physical systems exhibiting mechanical/thermodynamical regularity to living systems exhibiting adaptive and self-sustaining features therefore seems almost like an inversion of the most basic underlying physical tendencies of nature.2 Many of these features exhibit the signature of morphodynamic processes, and indeed, many theorists have equated living processes with such dissipative processes. A focus on the far-from-equilibrium dynamics of living systems was highlighted by Erwin Schrodinger"s effort to bring attention to their unusual thermodynamic tendencies, and it was a significant motivating factor in the pioneering studies of cyclic chemical processes by Manfred Eigen and of dissipative structures by Ilya Prigogine.3 Prigogine"s demonstration that dissipative systems are characterized by a tendency toward a maximum entropy production rate set the stage for the development of a quite sophisticated understanding of the augmentation of cla.s.sical thermodynamic theory, which was needed to explain chaotic and morphodynamic processes, as well as non-linear dynamical processes in general.
Living systems are characterized both by far-from-equilibrium thermodynamics and order production-the hallmarks of morphodynamics. So it is not surprising that living processes have often been equated with these processes. This has led to a widespread tendency to equate organisms with non-linear dissipative processes exhibiting merely morphodynamic features, and to a.s.sume that a dynamical systems theory account framed in these terms provides a sufficient explanation for living dynamics. This identification of life with self-organization has proved to be both a major step forward and yet also an impediment to developing a conception of living processes sufficient to account for their ententional characteristics.
This view has been eloquently articulated by a number of theorists. Thus Roderick Dewar argues that "Maximum entropy production is an organizational principle that potentially unifies biological and physical processes,"4 while A. Kleidon argues that "biological activity increases the entropy production of the entire planetary system, both living and non-living,"5 and Rod Swenson claims that "evolution on planet Earth can be seen as an epistemic process by which the global system as a whole learns to degrade the cosmic gradient at the fastest possible rate given the constraints."6 As we will see shortly, this last caveat ("given the constraints") is a critical qualification that ultimately becomes the tail wagging the dog, so to speak, in that it entirely undermines the universality of this claim when applied to life.
As we saw in the last chapter, it is well established that morphodynamic processes develop in persistent far-from-equilibrium conditions because the increase in internally generated dynamical constraints more efficiently (requiring less work) depletes the energetic and/or material gradient that is driving the system away from equilibrium. In this way, morphodynamic processes accelerate the destruction of whatever gradient is responsible for generating them. They are, in this respect, self-undermining, and are only maintained when this gradient is constantly replenished by some extrinsic source. This principle is eloquently stated by two major proponents of the view, E. D. Schneider and J. J. Kay, in an influential paper arguing for the relevance of maximum entropy production in characterizing organic and evolutionary processes. They state that As systems are removed from equilibrium, they will utilize all avenues available to counter the applied gradients. As the applied gradients increase, so does the system"s ability to oppose further movement from equilibrium. . . . No longer is the emergence of coherent self-organizing structures a surprise, but rather it is an expected response of a system as it attempts to resist and dissipate externally applied gradients which would move the system away from equilibrium.7 Living systems do indeed incorporate morphodynamic processes at nearly every level of their organization, from complex cycles of catalytic molecular reactions to the embryonic cellular interactions which determine the elaborate theme-and-variation organization of plant and animal body architecture. And yet in many respects organisms as whole dynamical systems, evolving lineages, or embedded within ecosystems also exhibit properties that differ radically from those characterizing morphodynamic processes. These include at least four ways that organisms invert the logic of morphodynamics: 1. Organisms depend on and utilize energetic and material gradients in their environment in order to perform work to sustain the constraints of their persistent, far-from-equilibrium dynamics, and to maintain constraints that are critical for countering the tendency toward thermodynamic decay.
2. Organisms actively reorganize their internal dynamics and relationships to the environment in ways that specifically counter or compensate for any depletion of the gradients that is necessary to maintain their dynamical integrity and their capacity to so respond.
3. Many organisms have evolved means of gradient a.s.sessment and spatial mobility that enable them to antic.i.p.ate and avoid conditions of depleted gradients and to seek out more optimal gradients.
4. Organisms and ecosystems evolve toward forms of organization that increase the indirectness of the "dissipation-path length" of energy and material throughput in order to extract more work from the available gradients.
In general, the ways that these processes all serve to maintain the capacity for self-repair and self-replication exemplify a clear inversion of the most typical features of morphodynamic systems. This indicates that dynamical systems approaches limited to morphodynamic and chaotic non-linear dynamics are insufficient to account for living dynamics. Life"s paradoxical dependence on morphodynamics, but its inversion of its most characteristic consequences, suggests that an additional dynamical inflection separates living processes from morphodynamic processes. This phase change thus exemplifies a further emergent transition (summarized in Figure 9.1).
Described in these general terms, we can begin to define the signature of this common higher-order dynamical logic. It is a dynamical form of organization that promotes its own persistence and maintenance by modifying this dynamics to more effectively utilize supportive extrinsic conditions. Importantly, such a dynamical organization is not identifiable with any particular const.i.tuents, or even any const.i.tuent morphodynamic process. It is this higher-order dynamical organization itself that is organized with respect to its own persistence, and precisely because it is not bound to specific material substrates or component dynamical process.
As we will see below, this fundamentally open and generic nature of living processes also means that they can additionally entrain and a.s.similate any number of intermediate supportive components and processes. This generic openness is what allows new functions and (in more complex organisms) new end-directed tendencies to evolve. By giving this general dynamical logic the name teleodynamics, we are highlighting this consequence-relative organization.
FIGURE 9.1: The nested hierarchy of the three emergent levels of dynamics; their typical exemplars; and their emergence (e) from subvenient dynamical processes.
LINKED ORIGINS.
It is a central hypothesis of this argument that the threshold zone between life and non-life corresponds to the fundamental boundary between teleodynamic processes and the simpler regimes of morphodynamic and thermodynamic processes. This does not necessarily mean that the origin of life is the only threshold leading to teleodynamics, or that only life can be teleodynamic. However, although the nature of this dynamical transition might prove to be quite generic-i.e., achievable in many ways in diverse kinds of substrates-there are good reasons to believe that the simplest (and perhaps the only) way that this threshold could be spontaneously crossed likely involves a simple molecular system; a first precursor to life as we know it.
So, although explaining the emergence of teleodynamics and investigating the origin of life are not the same enterprise, they are likely to inform one another. The non-life/life transition was both a critical threshold marking a fundamental phase change in dynamical organization, and yet must also have involved only a small number of const.i.tuent structures and processes, given that their synergistic coalescence occurred "accidentally." Being both fundamental and yet necessarily simple at the same time makes this a promising point of entry for explaining the origins of teleodynamic processes. Explaining the origins of life may actually be a more difficult task. Rather than focusing on the component structural or functional features of organisms per se, we can instead turn our entire attention to the dynamical problem itself, irrespective of particular planetary conditions and molecular specifics.
This is helpful because with respect to the origin of life, the specific molecular and geochemical details are daunting. Many of the dozens of essential molecular components of simple living cells have been considered as promising prerequisites to the formation of life, including nucleic acids, amino acids, phospholipids, sugars, purines and pyrimidines, and many mineral complexes and ions, such as involve phosphorus, iron, sulfur, calcium, chlorine, sodium, and so on. For this reason, it is often quite difficult to decide which few of these could be most primitive, and which should rather be considered acquired components that became essential only later in the evolution of life on Earth. More problematic is the fact that the most critical molecular const.i.tuents of even the simplest organisms are chiefly large complex molecules-polymers-that do not easily form spontaneously, and are easily broken up. Their production in cellular metabolism requires some of the most complex combinatorial molecular processes in existence.
Discerning the essential primitive dynamics of life is similarly clouded by life"s current complexity, and because the evolutionary process has likely erased most traces of life"s earliest, minimally sufficient precursors. Indeed, because of this necessary simplicity, the first molecular systems able to spontaneously achieve the dynamical basis for a quasi-evolutionary process inevitably lacked many of the characteristics found in contemporary life forms, and yet they would need to be teleodynamic.
Definitions of life based on generalizations derived from functional features found in all living creatures typically cite molecular replication, cell division, energy metabolism, semi-permeable membranes, and the maintenance of far-from-equilibrium chemical processes as minimal characteristics, with perhaps a few others. Because the probability of the serendipitous chance coalescence of even a few of the molecular types and dynamic interdependencies necessary to produce these effects is vanishingly small, scenarios for the origins of life have had to envision ways that a much smaller set could be spontaneously a.s.sembled, often utilizing aspects of life that show some degree of self-a.s.sociation and ancillary environmental support (lipid "bubble" formation, the catalytic-template possibilities of clays, etc.).
The explosive plurality of dynamic features and molecular species to choose from has led to quite diverse scenarios and contrived arrangements between presumed early terrestrial environments and molecular processes. It is not even clear what criteria could be used to rank the plausibility of these alternatives.
Finally, organisms are both components and products of the evolutionary dynamic in much the same way as biomolecules are both components and products of the synthetic network that const.i.tutes a cell. For the same reason, organisms and the evolutionary process are not separable. Explaining life requires explaining its evolutionary predisposition, because it must have emerged coextensive with whatever form of molecular teleodynamic process characterized the dawn of life. These conditions necessarily created a persistent natural selection dynamic that enabled the acc.u.mulation of additional supportive molecular processes. So, identifying the minimal, spontaneously probable, molecular conditions for life should also provide the minimal conditions for natural selection.
This more abstract focus on its distinct dynamical properties will enable us to ignore many incidental features of biology and molecular chemistry. Instead of attempting to discover what attributes of living cellular chemistry are dispensable, without losing essential living functions, or what environmental conditions were the most likely to have given rise to the first living systems, we can focus attention on the more general problem of accounting for the phase change in dynamical organization that necessarily occurred with the origins of life, irrespective of any specific molecular details.
Consider again the basic teleological glosses given to processes in even the simplest life forms. Living organisms are integrated and bounded wholes, const.i.tuted by processes that maintain persistent self-similarity. These processes are functions, not merely chemical reactions, because they exist to produce specific self-promoting physical consequences. These functions are adaptive and have evolved with respect to certain requirements in their environment that may or may not obtain. And these adaptations exist for the sake of preserving the integrity and persistence of these integrated systems and the unbroken chain of ancestral forms for which they are the defining links.
In other words, as Stuart Kauffman has emphasized, organisms are spontaneously emergent systems that can be said to "act on their own behalf" (though "acting" and "selfhood" must be understood in a minimal and generic sense that will be developed further below).8 Since they may incidentally encounter favorable or unfavorable environments, organisms must embody a tendency to generate structures and processes that maximize access to the former and minimize exposure to the latter, in such a way that these capacities are preserved into the future. By virtue of these properties that we easily recognize in organisms, we see the most basic precursors of what in our mental experience we describe as self, intention, significance, purpose, and even evaluation. These attributes, even in attenuated form, are significantly unlike anything found spontaneously in the non-living world, and yet they inevitably emerged in their most basic form first in systems far simpler than the simplest known organisms-systems characterized by an unprecedented form of dynamical organization.
COMPOUNDED ASYMMETRIES.
As we have seen, both orthograde and contragrade processes are asymmetric processes of change, irrespective of whether cast in thermodynamic or morphodynamic terms. Living and mental processes are problematic not only because of their causal asymmetry, but also because of the unusual nature of their particular asymmetries. Their orthograde tendencies are triply complicated compared to the orthograde asymmetry of thermodynamic processes. This is what provides their final causal character.
Consider, first, the end-directed processes a.s.sociated with life. Even the simplest organisms exhibit organizational features for which there are no non-living counterparts. They tap external energy sources to do work to transform raw materials from their surroundings into the components to construct their own bodies, and they involve far-from-equilibrium chemical reactions that collectively oppose thermodynamic degradation by continually maintaining critical boundary conditions and by synthesizing and replacing components that have degraded.
H. Maturana and F. Varela, focusing on the generative nature of the process, have called this process autopoiesis, which literally means "self-forming."9 Mark Bickhard, focusing on the stabilization of dynamical self-similarity, called this form of dynamical organization recursive self-maintenance, to distinguish it from the simpler self-maintenance exhibited by non-equilibrium processes that persist in a similar dynamic state because of deviation-minimizing boundary conditions. Bickhard"s paradigm example of simple self-maintenance is a candle flame because the heat of the flame melts and vaporizes a limited volume of wax so that it is capable of ignition to create heat, and so forth.10 Stuart Kauffman has additionally highlighted the fact that maintenance of systemic self-similarity const.i.tutes an autonomous individual, or as he terms it, an autonomous agent.
Teleodynamics is not identical with any one of these. Each in a slightly different way attempts to characterize in abstract terms the dynamical characteristics distinctive of life, with an eye toward their possible wider application. Teleodynamics can also be understood as characterizing the distinguishing dynamics of life. However, rather than being an abstract description of the properties that living processes exhibit, it is a specific dynamical form that can be described in quasi-mechanistic terms. Although it is the distinguishing characteristic of living processes, it is not necessarily limited to the biological domain. Teleodynamic processes can be identified with respect to the specific end-directed attractor dynamics they develop toward. And they are characterized by their dependence on and emergence from the interactions of morphodynamic processes. Teleodynamics is the dynamical realization of final causality, in which a given dynamical organization exists because of the consequences of its continuance, and therefore can be described as being self-generating. Specifically, it is the emergence of a distinctive realm of orthograde dynamics that is organized around a self-realizing potential, or-to be somewhat enigmatic-it is a consequence-organized dynamic that is its own consequence.
As we discovered in the last chapter, the signature of an emergent transition is the appearance of an unprecedented form of higher-order orthograde change-a pattern of asymmetric change that occurs spontaneously, due to the amplification of interaction constraints at a lower level producing a discontinuous break from the lower-order orthograde asymmetries that contribute to it. This is doubly true of teleodynamics. Not only do we observe the emergence of living dynamics and the functions that const.i.tute it, but also this gives rise to the emergence of natural selectionlike processes. So, while individual organisms may be doing local work with respect to their own survival and reproduction, these spontaneous processes do not lend their asymmetric character to the larger evolutionary dynamic. The process of evolution, rather than merely maintaining and reproducing dynamical form, exhibits a spontaneous tendency for its dynamics to diversify and complexify these forms, both intrinsically and in their relationships to their contexts. Thus evolution is neither pushed by intrinsic forces of development nor pulled toward a goal of greater complexity and efficiency. It effectively "falls" in these directions. It is, as noted above, an orthograde process.
Both Varela"s notion of autopoiesis and Kauffman"s characterization of autonomous agency are exemplified by self-repair and self-reproduction. As we will see, these are not independent processes, but two sides of the same dynamic. The synthesis of replacement components and the stabilization of system organization are critical to both organism self-maintenance and reproduction. Together, they const.i.tute the crucial counterdynamics to the relentless tendency toward thermodynamic degradation. To resist this spontaneous degrading influence requires work. The maintenance of non-equilibrium conditions is thus essential, both for stabilization and for the generation of replacement components, a.n.a.logous to the constant effort that is required to keep an office in order or an engine running despite constant use and wear and tear. For this reason, the need for constant repair is the inevitable predicament of life in general. And the work required is not merely energetic. The incessant need to replace and reconstruct organism components depends upon synthetic form-generating processes, not merely resistance to breakdown.
For this reason, teleodynamic processes are inevitably dependent on morphodynamic processes for their form-generating capacity. As we"ve seen, morphodynamic processes are dependent on the maintenance of far-from-equilibrium thermodynamic conditions. So the dependence of teleodynamics on morphodynamics and morphodynamics on thermodynamics const.i.tutes a three-stage nested hierarchy of modes of dynamics, which ultimately links the most basic orthograde process-the second law of thermodynamics-with the teleodynamic logic of living and mental processes. That being said, it remains to be shown exactly how this additional phase transition in causal dynamics is accomplished. Just as we have traced the logic of the transition from thermodynamic to morphodynamic processes, it is now necessary to do the same from morphodynamic to teleodynamic processes.
There are reasons to suspect that this additional emergent phase transition exhibits features that are a.n.a.logous to those involved in the transition from thermodynamic to morphodynamic processes. The orthograde dynamics that characterize a morphodynamic process emerge from thermodynamic processes that are in effect pitted against one another, in complementary ways. In the case of Benard cells, for example, continuous heating constantly undermines the increase in entropy of the fluid medium and its tendency to destroy this heat gradient. So, although the spontaneous thermodynamic orthograde process never ceases, it can never converge toward its attractor: equilibrium. Like Sisyphus in Greek mythology, who finds himself doomed to continually roll a boulder uphill, or Alice and the Red Queen in Lewis Carroll"s Through the Looking-Gla.s.s, who must run fast just to stay in the same place, the conditions underlying this new orthograde attractor are in a delicate balance. This a.n.a.logy suggests that the transition to teleodynamic organization is likely the result of a higher-order balance between persistent morphodynamic tendencies arranged in some kind of opposing but complementary relationship with respect to one another-one that also keeps both from ever reaching their ultimate thermodynamic end state.
The simplest systems we know of that exhibit teleological properties are simple organisms, like bacteria. It might seem prudent to look to the simplest life forms for clues to how such complex convoluted dynamics might form. But living organisms are immensely complex. The organisms currently living are the end products of 3.5 billion years of evolution, in which there have been vast changes to almost every aspect of their molecular components and functional organization, as well as ma.s.sive complexification. The differences between physical systems lacking these key features of life and even the simplest living organisms are immense.
As we have also noted, a spontaneous transition from chemical interactions lacking these features to an integrated chemical system const.i.tuted by them cannot have involved even dozens of the hundreds of specialized interdependent molecules and chemical reactions that currently play the core roles in simple organisms. This ill.u.s.trates an important point.
Although the transition from a non-teleological chemical dynamic to the first teleodynamically organized molecular system const.i.tuted a fundamental transition in the cosmic history of causality (on Earth or wherever else it also occurred), it necessarily involved a simple combination of molecular processes. It is not the complexity of the transition that was critical, but the appearance of a fundamentally different orthograde dynamical organization. The initial crossing of the dynamical threshold to a primitive form of teleodynamics should therefore not be beyond our current scientific tools, though it may involve overcoming certain tacit a.s.sumptions.
SELF-REPRODUCING MECHANISMS.
A core feature of life that in many respects exemplifies the most basic ententional properties is its self-reproductive capacity. Indeed, it will turn out that in a more completely a.n.a.lyzed form, this capacity is one of the defining features of a teleodynamic process. But reproduction in this sense is not merely pattern replication or copying. It is rather the construction of a dynamical physical system which is a replica of the system that constructed it, in both its structural and functional respects, though not necessarily a faithful replica in every detail. Self-reproduction is thus an end-directed dynamic in which the end is only a potential general form represented within the dynamical system that produced it, but which is a physical system with the same general properties of its progenitor.
One of the first formal a.n.a.lyses of the physical requirements for a mechanism to be considered capable of self-reproduction came from the work of the mathematician John von Neumann, a pioneer of modern computer design. In a short 1966 monograph, he explored the logical and physical problem of machine self-reproduction. His explorations of the logical requirements of self-reproduction followed the insights of the then-new DNA genetics by conceiving of reproduction as an instruction-based process that could be modeled computationally. He argued that a device capable of constructing a complete replica of itself (that also inherits this capability) must include both a.s.sembly instructions and an a.s.sembly mechanism capable of using these instructions to a.s.semble a replica of itself, including the tokens encoding the instructions. In simple terms, his criterion for self-reproduction is that the system in question must be able to construct a copy of itself, that also possesses this constructive capability. But specifying how to construct a mechanism with this capability turns out to be much more difficult than this simple recipe might suggest.
Von Neumann and subsequent researchers explored the formal requirements of self-reproduction almost exclusively via simulation-for example, in cellular automata-because it was quickly recognized that specifying what he called a "kinetic" model of self-reproduction with autonomous means for substrate acquisition and structural a.s.sembly adds highly problematic material constraints and energetic demands that rapidly expand the problem into the realms of physics, chemistry, and mechanical design. He envisioned the process as involving two distinct components: a universal constructor and a universal description. As he outlined the process, the universal constructor would somehow read off instructions for building another constructor device and then transfer a copy of the instructions to the new mechanism. The description could therefore be embodied in a pa.s.sive artifact, like a physical pattern. But while he was able to specify the self-replication process in formal terms (laying the groundwork for how one would construct an algorithm capable of replicating itself within a computer) the design of the kinetic constructor was another story. Indeed, von Neumann considered the problem of the material basis of this process to be far more critical than its formal implementation.11 In the decades since von Neumann outlined the problem, many software simulations of natural selection processes have been developed. The field that has grown up around this work is often described as artificial life (or A-Life). But the goal of physically implementing machine self-reproduction-von Neumann"s kinetic self-reproducing machine-as opposed to merely simulating it, has not been achieved. So, while the field of A-Life has had an explosive and productive growth in the decades since his death, little progress has been made toward implementing this idea in kinetic terms. The big difference is, of course, that the production of computer code is entirely parasitic on the physical work done by the computer mechanism. Issues of component synthesis, access to free energy and substrates, and translating the instructions into actions can thus be entirely bracketed from consideration. Of course, these material-energetic entailments are what critically matter. Without them, instructions are merely inert physical patterns.
Physically embodied (rather than simulated) self-reproduction requires one physical system to construct another like itself. This requires physical work to modify physical materials, which requires a mechanism able to access free energy, a mechanism to use this energy to manipulate substrates to transform them into self-components, a mechanism that organizes and a.s.sembles these components into an appropriately integrated system, and a means to maintain, implement, and replicate the constraints that determine this integrated organization. And if the system is to be capable of evolving, it must also be sufficiently tolerant of structural-functional degeneracy to allow some degree of component replacement and dynamical variation without losing these most basic capacities.
This is, of course, only a list of what must be accomplished by a kinetic self-reproduction process. It is not an account of how it can be physically accomplished. And this, as we have seen, is the real problem: explaining how living processes do their end-run around the ubiquitous second law of thermodynamics. Knowing what has to be accomplished is a first step; but it is far from knowing how to do it, or even whether it is physically possible. In the biological world (in contrast to the virtual world of computer simulations), life requires the constant acquisition of energy and raw materials from its environment, and an incessantly active, tightly orchestrated use of these to stay ahead of the ravages of thermodynamic decay.
Only in the abstract can we ignore how reproduction is accomplished and focus on the forms being copied. Artificial life simulations, for example, can simply a.s.sume the availability of an a.s.sembly mechanism and resources to supply the material and energy to reproduce their representations, as all these physical details are built into the computer"s most basic operations of copying and modifying memory register patterns from one location to another. Although it should be possible for a simulation to take the computer"s energetic usage, storage s.p.a.ce requirements, and the physical features of the medium into account in determining differential replication-features that might be useful for software designers-these physical correlates of computing are not generally of interest to modelers of evolutionary processes. Moreover, the specific relevant thermodynamic features of interest (food, protection from predation, etc.) can themselves be represented in data form, as can energy use and development. Even so, all the physical attributes of the computing process itself are ignored. Even though thermodynamic requirements and ecological resources can be incorporated into a model, this crucial feature makes a simulation less than reproduction and evolution. What is most fundamental to these processes is that they are at base thermodynamically grounded. In the course of evolution, any incidental physical attributes of the mechanisms that embody these operations and substrates can become subject to selection, and thus part of what must be represented and reproduced.
For example, although the redness of hemoglobin is not critical to its oxygen-ferrying capacity, and is merely a side effect of this being done using an iron atom, if the redness of blood became a feature that a deadly parasite used to locate its victims, there would almost certainly be selection to alter or mask this color. In this way, evolution constantly transforms incidental physical attributes of organism dynamics into functionally relevant information that must be pa.s.sed from generation to generation. This is a fundamental feature that distinguishes biological evolution from evolution modeled in silico-a distinction that is lost when only focusing on the information side of evolution. Ignoring this energetic-material-formative half of the explanation effectively traps us in a dualistic conception of life.
WHAT IS LIFE?.
Erwin Schrodinger is the physicist responsible for the equation that describes the statistical logic of quantum mechanics: a wave function of probability that effectively marks the doorway between quantum and cla.s.sical physics. But he is also responsible for a very different and equally revolutionary insight in another science-biology-though he would never have claimed to be a biologist. In the early 1940s, he gave a series of lectures that resulted in a small book with the t.i.tle What Is Life? In it he asked two quite general and interesting questions about the physical nature of life, and offered some general speculations about what sort of answers might be expected.
The first question concerned the energetics of life. Living organisms, individually and in the grand sweep of evolution, appear to make an end run around one of the most fundamental tendencies of the universe, the second law of thermodynamics. From a physicist"s point of view, this ubiquitous feature of life is more than just curious. It demands an explanation of how such a counterintuitive trick is performed by the chemistry of organisms, when chemistry by itself seems to naturally follow the thermodynamic law to the letter.
The second question was indirectly linked to the first. How could the chemistry of life embody the information necessary to instruct the development of organisms and maintain them on a path that defends against the incessant increase of entropy? In other words, what controls and guides the formation and repair of organism structures to compensate for the ravages of thermodynamics and just plain accident, and what makes it possible for living processes to be organized with respect to specific ends, such as survival and reproduction?
Schrodinger"s general answer to the first question was that living chemistry must somehow be continuously performing work to stave off the pressures of thermodynamic decay, and to do this it needs to feed off of sources of free energy available in the outside world that he enigmatically called "negentropy," or sources of order. His general answer to the second question was that there must be a molecular storage medium available to organisms, which embodies a chemically arbitrary and interchangeable but functionally distinguishable molecular pattern that can be preserved and copied and pa.s.sed to succeeding generations. He envisioned a medium that he metaphorically described as an "aperiodic crystal." He speculated that at the heart of every organism, and indeed every living cell, there must be something akin to a crystal, because it would have to have repeatable units, and yet it would have to be non-crystalline in another way, since these units need to be slightly varying, unlike mineral crystals, which are highly regular. He reasoned that in order to be able to store information, each unit cell of this crystallinelike molecule would need to exhibit one of a number of structurally different but energetically equivalent states, not unlike the way that the typographical characters of this sentence are interchangeable.
This turned out to be a remarkably prescient generic description of the properties of DNA molecules. And not surprisingly, Watson and Crick"s account of DNA structure, described a few years later, was influenced by this vision. Though many biologists proclaimed that the discovery of DNA and its chemistry "solved" the riddle of life, or const.i.tuted the "secret of life," this was only half the mystery that Schrodinger had envisioned. It did not address the thermodynamic problem.
In comparison to his contribution to the search for the informational basis for genetic inheritance, Schrodinger"s attention to the thermodynamic riddle of life, and his intuition that these two mysteries must be intrinsically linked, fell into the background of biological discussion, to be followed up by a comparatively small group of theoretical biologists. In the generations since Schrodinger, the exploration of the riddle of life has mostly been characterized by parallel and often non-interacting threads of research in these two domains; and the progress has been mostly one-sided. For the most part, the vast majority of evolutionary and molecular biologists have followed the trail of molecular information, while a much smaller cadre of physicists and physical chemists have followed the trail of far-from-equilibrium thermodynamics. This is ultimately an untenable segregation, because information turns out to be dependent on thermodynamic relationships. An explicit effort to reunite these two theoretical domains will have to wait until chapters 12 and 13; but even without an explicit theory of information, the relationship of these processes to the origins of teleodynamics can be explored in some detail.
What Schrodinger"s questions do not approach is how this physically atypical state of affairs came about, and why they must be linked. Exploring this riddle will provide the first steps toward reconstructing the bridge leading from the non-living, non-feeling, non-knowing world to the world of life and mind.
FRANKENCELLS.
One way to approach the question of what is minimally necessary to define life is to start with what we have, and then subtract features until the removal results in failure to function. Attempting to produce artificial exemplars of minimal living cells has currently relied on two general approaches. Laboratory-based approaches to identify the minimal conditions for life are generally distinguished as top-down approaches. Top-down approaches attempt to extrapolate backwards, theoretically and experimentally, from current organisms to simpler precursor organisms. Prominent in this paradigm is the attempt to describe and produce "minimal cells" by stripping a simple bacterium of all but its most critical components.12 Though considerably simpler than naturally occurring organisms, these minimal cells still contain hundreds of genes and gene products,13 and so turn out to be vastly more complex than even the most complex spontaneously occurring non-living chemical systems, implying that they cannot be expected to have formed spontaneously.
The alternative bottom-up approach attempts to generate key system attributes of life from a minimized set of precursor molecular components. An increasing number of laboratory efforts are underway to combine molecular components salvaged from various organisms and placed into engineered cellular compartments called protocells.14 The intent is to produce an artificial "cell" with the capacity to maintain the molecular processes necessary to enable autonomous replication of the entire system. To accomplish this, protocells must obtain sufficient energy and substrates and contain sufficient molecular machinery to replicate contained nucleic acid molecules and to produce the protein molecules comprising this machinery from these nucleotide sequences-and probably much more. Though vastly simpler than what is predicted for a minimal bacterial cell, even the most complex protocell systems fall considerably short of the goal of achieving persistent autonomous reproduction, even though they incorporate dozens of complex biomolecules (nucleic acids, complex proteins, nucleotides, phospholipids, etc.). In most cases these molecules are already organized into working complexes (such as ribosomes) by the living systems from which they have been removed. Given that they are composed of cellular components that accomplish the relevant functions in their sources, it is expected that protocell research will accomplish its goal as more complex protocells are constructed. However, even the simplest protocells currently imagined are sufficiently complex to raise doubts that such systems could coalesce spontaneously from pre-organic substrates.
An implicit a.s.sumption of the great majority of these approaches is that replication and transcription of molecular information, as embodied in nucleic acids, is a fundamental requirement for any system capable of autonomous reproduction and evolution. This is a natural a.s.sumption since nucleic acidbased template chemistry is the most ubiquitous attribute of all known forms of life. But despite its intuitive attraction and laboratory accessibility, a.s.suming the spontaneous appearance and both the replicative and protein template functions of nucleic acids brings with it impossible demands.
First, including nucleic acid replication in an artificial cell is extremely demanding in terms of critical support mechanisms. In order to replicate nucleic acid sequences and transcribe them into protein structure, some of life"s most complex multimolecular "machines" are required. Each of the macromolecular complexes supporting the various aspects of this process (replication, translation, transcription, etc.) typically consists of over a half dozen different interlocking and synergistically interacting molecules. The precise stereochemical demands placed on the major protein units of these complexes are reflected in the highly conserved gene sequences for each, which have undergone little change since before the epoch of eukaryotic cells. They are almost certainly the product of long evolutionary fine-tuning for this function. Though some of these complications may be avoided by molecules serving multiple functions, such as the capacity for RNA to also exhibit catalytic functions,15 an impressive number of these complex molecular structures and interactions must still be provided to support such processes. For this reason, protocells based on these known core molecular processes of life provide valuable test beds for exploring how subsets of these molecular mechanisms contribute to replication. But we should be wary of using this approach to model the earliest forms of life.
If the goal is to engineer life as we currently understand it, then building a protocell capable of reproducing itself const.i.tutes success, no matter how its parts are obtained. But engineered cells built from molecules found in living organisms are likely to provide a rather misleading model for studying how life began. Before life got a foothold in our solar system, few if any of these components were present, and of course there were no engineers to select the critical molecules and appropriately a.s.semble them into working complexes within a cellular container. Stripped-down, modified viruses are already in widespread use in biomedical research, and artificial bacterial protocells are almost certainly just around the corner. Creating a stripped-down artificial bacterium or protocell that can reproduce itself will certainly provide important insights about life in general. It is quite likely that such cells could provide useful vehicles for replicable nanomachines functioning at a cellular scale. But protocells are unlikely to be useful models for the missing link between physics and biology.
Protocells are Frankencells, like the unfortunate "monster" of Mary Sh.e.l.ley"s now prophetic tale of a revivified cadaver. They are reconstructed by recombining components extracted from once-living cells, in the hopes of revivifying the experimental combination. But like the cadaver pieces st.i.tched together by the fictional Dr. Frankenstein, these cellular components were the product of billions of years of evolutionary fine-tuning for their respective interdependent roles. Starting with these end products is like using computer components to explain the construction of the first abacus.
So, in three respects, making sense of the spontaneous emergence of a teleodynamic molecular system from non-ententional antecedent conditions is more challenging than simply reverse engineering simple organisms. First, unlike approaches using complex biomolecules as building blocks, we cannot a.s.sume to take advantage of the products of prior evolutionary (and thus teleodynamic) processes to explain how the various components arose and came to work together. Second, the components we can consider must be synthesized by spontaneously occurring non-biological processes. And third, it is not enough to have components merely brought into proximity with each other; they must reciprocally produce one another and maintain their synergistic relationships. Merely collecting the critical molecular components of cells into a cell-like container will not suffice, even if they perform the chemical functions they would provide to a naturally evolved organism. This even applies to the self-replication of nucleic acids. In the absence of the synergistic co-production of all components, we have nothing more than an organic chemistry experiment carried out in a tiny lipid reaction vessel.
One difficulty in thinking about this issue more broadly derives from the lack of exemplars of extraterrestrial life for comparison. This limits our ability to discern essential from incidental features of life. Since many of the widespread or even universal features of living chemistry might well have been incidentally acquired due to unique features of the Earth environment, focusing too narrowly on the chemistry of specific biomolecules-even DNA-could overly limit the scope of the search. A related difficulty arises due to the absence of life forms that are more primitive than the simplest contemporary species (e.g., of bacteria). It is certain that even the simplest contemporary organism is far more complex than could form spontaneously. Over the course of 3.5 billion years of evolution on Earth, it is almost inevitable that innumerable early stages of life"s precursors have been replaced so that nearly all traces of these stages are gone. Finally, efforts to produce artificial systems with these properties, but composed of const.i.tuents not found in organisms, are still in their infancy. So the range of possible alternative mechanisms for the key properties of living systems remains largely unexplored.16 These limiting circ.u.mstances make the deconstruction of living organisms for clues about the earliest transitional stages unlikely to succeed.
Ultimately, the cosmos must have achieved this transition with a system of molecular processes that is far simpler than anything resembling life as we know it today. As will be discussed in chapter 12, the property that is usually considered most central to life-information-is unlikely to be a primary player in this early transition, and as we will further develop the concept of information in chapters 13 and 14, it will become apparent that information in the full sense of the term (which is both about something and has normative characteristics) is not a primary property of matter, but is dependent on underlying teleodynamic processes. Moreover, DNA-based processes are far too complex to have appeared spontaneously and fully developed. The possibility that molecular structure could be information about something (e.g., the chemical dynamics of a cell with respect to its likely environments) is necessarily a higher-order emergent function abstracted from and dependent on more basic teleodynamic processes. To put this in terms of Schrodinger"s dual characterization of life as a marriage between transmission information and non-equilibrium thermodynamics, the informational functions of life are emergent from and dependent on more basic non-equilibrium dynamical processes.
Hints about how this might be possible have come from work by researchers exploring the physical chemistry of the synthetic and metabolic processes that ultimately support the replicative and informational functions of cells.17 Rather than thinking in terms of life"s current well-honed tool kit, these researchers ask what general dynamical operations are accomplished by these mechanisms? Generalizing the notions of metabolism and containment, respectively, we can describe these processes in terms of their roles in countering two thermodynamic challenges. First, there must be a mechanism that counters the incessant tendency for component elements of the system to degrade-either by repairing damaged components or by synthesizing new ones. And second, there must be a mechanism that resists the degradation of constraints on potential interactional relationships among components, such that the critical synthetic processes are reliably achieved. The compatibility of this approach with the goal of explaining the origins of teleodynamics is that both approaches a.s.sume that the informational functions of life emerge from simpler dynamical foundations.
10.
AUTOGENESIS.
. . . an organized natural product is one in which every part is reciprocally both end and means.
-IMMANUEL KANT"S PRINCIPLE OF "INTRINSIC FINALITY," 1790.
(ITALICS IN THE ORIGINAL)1.
THE THRESHOLD OF FUNCTION.
Even though there is a close interrelationship between them, investigating the mystery of the origins of life and the origins of teleodynamics requires quite different approaches. All current approaches to the origins of life on Earth begin from tacit and una.n.a.lyzed a.s.sumptions about the nature of the basic unit of life: an organism, with its physical boundedness, functional organization, and heritable information. These a.s.sumptions are typically glossed as though they can be defined by intuitively obvious physical-chemical properties such as containment in a lipid membrane, metabolic processes powered by ATP, and information intrinsically embodied in nucleic acids. These glosses allow us to a.s.sume what we should be explaining: why these same structures and relationships do not have intrinsic functional or informational character except when embodied in living dynamics. It is their interdependent contribution to const.i.tuting the dynamical system that is an organism, and not any of their intrinsic properties that matters.
So, even before the question of how these components collectively const.i.tute these properties, we need to understand the nature and origins of this form of collective organization itself. But whereas life demands an account of its molecular peculiarities, teleodynamics merely demands an account of its dynamical requirements. Instead of considering which compositional features matter, we can be somewhat agnostic about composition and begin to pay attention to this dynamical organization, and inquire into how it const.i.tutes this transition. In other words, to simply a.s.sume that ententional issues can be operationally ignored or a.s.sumed as given, so long as we have the right molecules, is to fall prey to the homunculus fallacy. These properties are not intrinsic to the material const.i.tuents of life. Ententional properties like function and information will only be explained when we can demonstrate how they emerge from non-ententional precursors, and so the teleodynamic processes that characterize life must be explained (though not reduced) by reference only to thermodynamic and morphodynamic precursors.