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The teleological transitions in evolution: A Gántian view
Journal of Theoretical Biology 381 (2015) 55–60
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Journal of Theoretical Biology journal homepage: www.elsevier.com/locate/yjtbi
The teleological transitions in evolution: A Gántian view Simona Ginsburg a, Eva Jablonka b,n a b
Natural Science Department, The Open University of Israel, Raanana 43107, Israel The Cohn Institute for the History and Philosophy of Science and Ideas, Tel-Aviv University, Tel-Aviv 69978, Israel
H I G H L I G H T S
Approaching Aristotelian teleological systems from an evolutionary perspective. Describing Gánti's strategy for the study of minimal life. Discussing Gánti's transition marker for life: unlimited heredity. Applying Gánti's strategy to the evolutionary transition to minimal consciousness. Suggesting a transition marker for consciousness: unlimited associative learning.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 March 2015 Received in revised form 5 April 2015 Accepted 7 April 2015 Available online 15 April 2015
We discuss Gánti's approach to the study of minimal living organization, and suggest that his methodology can be applied to the study of the two other major teleological systems described by Aristotle: minimal consciousness (sentience, experiencing) and rationality. We start by outlining Gánti's strategy for the case of life: listing the basic characteristics that any living system capable of open-ended evolution must satisfy, developing a dynamic model that instantiates these characteristics (the chemoton), and identifying a capacity of the system (unlimited heredity) that allows the system to dynamically persist over evolutionary time and to be used as a marker of the evolutionary transition to life. We apply Gánti's explanatory strategy to the evolutionary transition to minimal consciousness, suggest a transition marker (unlimited associative learning) and discuss the wider evolutionary and philosophical implications of this approach. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Chemoton Consciousness Origin of life Transition marker
1. Introduction Gánti's contribution to the study of minimal life is now well recognized, and many of the papers in this issue show his longlasting influence on research in the fields of systems-chemistry and the origin of life. However, what we want to show is how Gánti's approach to the study of minimal-life can be extended and used more generally for studying the origins of the two other great teleological systems: basic animal consciousness (which is our focus here), and human rationality and symbolic values. The analysis of living systems in terms of their goal-directedness has deep roots in Western philosophy. In On the Soul, Aristotle carved the living world at its teleological joints and suggested that the “soul” (psyche) is a principle of living organization that has three hierarchically-ordered incarnations. The first and most basic, which is manifested even in plants, is the reproductive or nutritive soul,
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Corresponding author. E-mail addresses: [email protected] (S. Ginsburg), [email protected] (E. Jablonka). http://dx.doi.org/10.1016/j.jtbi.2015.04.007 0022-5193/& 2015 Elsevier Ltd. All rights reserved.
which is characterized by growth and generation and has the goal of survival and reproduction. The second incarnation is the sensitive soul, the soul of animals, which is built on the nutritive one and is characterized by sensation, movement, desire and motivation (and in some animals also imagination); its teloi (goals) are the satisfaction of felt needs and passions. The third, the rational soul (in mortal humans), is built on the previous two, and is characterized by rational thinking and striving for abstract symbolic teloi: for moral and esthetic values like the good and the beautiful. One can look at these Aristotelian goal-directed systems from an evolutionary point of view, seeing their origins in terms of evolutionary transitions from one state to another. The transition to Aristotle's nutritive soul is the transition to the first living system(s), which is the research topic to which Gánti contributed most directly; although studying the origin of life from the inanimate still presents great challenges, it has ceased to be a conceptual mystery (at least to most scientists and many philosophers). The second transition is the transition to consciousness, the evolutionary origin of Aristotle's sensitive soul; its study is shrouded in more conceptual fog and is only just beginning to gain momentum. The third is the transition to rationalizing-symbolizing animals, to
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Table 1 Representative lists of characteristics of minimal living systems [Gánti's list is highlighted]. Author
Characteristics
Emphasis
Lamarck (1809)
1. Individuality; 2. Birth and development; 3. Special flux (electricity and caloric) dynamics; 4. Nutrition and controlled growth; 5. Manufacturing components of self; 6. Reproduction and multiplication; 7. Mortality 1. Inherent unity; 2. Metabolism; 3. Inherent stability; 4. Information-carrying sub-system; 5. Program control; 6. Growth and multiplication; 7. Hereditary system enabling open-ended evolution; 8. Mortality 1. Individuality (closure); 2. Self-production; 3. Responsiveness; 4. Regulation and selectivity
Self-organization, metabolism Self-organization; evolution Metabolism, autopoeisis
1. Functionally complex organization; 2. Natural selection can occur; 3. Replication of a genetic material; 4. Information for specifying the living system stored in stable chemical molecules 1. Complexity and organization; 2. Chemical uniqueness (living organisms are composed of large polymers); 3. Quality (some relations between aspects of the living world can only be described qualitatively); 4. Uniqueness and variability; 5. Possession of a genetic program; 6. Historical nature; 7. Natural selection can occur; 8. Indeterminacy (biological systems have emergent properties) 1. Manufacturing its own constituents; 2. Extracting energy and converting it to work for the system; 3. Catalyzing system's reactions; 4. Having information systems enabling re-production; 5. Closure (individuality); 6. Regulation; 7. Multiplication 1. Self-organization; 2. Autonomy; 3. Emergence; 4. Development; 5. Adaptation; 6. Responsiveness; 7. Evolution; 8. Reproduction, growth; 9. Metabolism
Information, evolution
Gánti (1971, 1987) Maturana and Varela (1973) Orgel (1973) Mayr (1982)
De Duve (1991)
Boden (2009)
Evolution
Metabolism
Information, autopoiesis, evolution
Aristotle's rational (human) soul; this is one of the hottest topics in present-day evolutionary-cognitive biology, although its study goes all the way back to Darwin. Although all of Aristotle's goal-directed systems are the products of chemical and biological evolution, the way they are organized and how they evolved are major questions for evolutionary biologists and philosophers. To show how the way in which Gánti approached the study of living organization has not only shed light on the transition to life but can also provide a framework for understanding other teleological transitions, we start by outlining Gánti's strategy in accounting for living organization. We then show how adopting this strategy can shed light on the study of animal consciousness.
2. Gánti's strategy: the list, the dynamics, and the transition marker In his seminal book, The Principle of Life, Gánti (1971, 1987) described his chemical model of minimal life. He started by listing the basic characteristics that any living system capable of openended evolution must satisfy. As Table 1 shows, his list in many ways is similar to those of others. However, Gánti's major interest was not to characterize life in the abstract, but to describe the minimal system that can instantiate the formal and functional properties of life on earth. Gánti constructed an abstract chemical dynamical model, the chemoton (Fig. 1), which instantiated the eight criteria of life that he considered to be essential; five of them (1–5) are “absolute”, in the sense that life cannot exist without them; and three of them (6–8) are “potential”, which means that living forms having these properties can undergo open-ended evolution leading to the emergence of extant, complex, life forms. The ability to generate the vast number of hereditary variations on which the capacity for open-ended evolution rests is the hallmark of all the forms of life we know, and depends on all the other criteria in Ganti's list. It is what we call the transition marker for life. Although not himself involved in prebiotic geochemistry research, Gánti suggested that his list of criteria and his chemoton model could be used to constrain and guide the construction of concrete, geochemicallyinformed scenarios of the early processes on earth that led from chemistry to biology. In spite of the many questions left open by the chemoton model [discussed by Griesemer and Szathmáry in their commentaries on the later edition of Gánti's book (Gánti, 2003)], in the decades since it was constructed it has proved to be a useful guide for theoretical and empirical approaches to the origin of life (see papers in this issue). It is an example of what Maturana and Varela (1973) called an autopoietic system: a system whose
Fig. 1. Gánti's chemoton is made up of three tightly coupled subsystems: the autocatalytic metabolic cycle (abcde cycle), the informational cycle that generates the polymer, and the membrane-forming subsystems. [Based on Gánti, 2003, Fig. 1.1, p. 4), Maynard Smith and Szathmáry (1995, p. 20–23) and the modification of this figure in Jablonka and Lamb (2006, Fig 1, p. 237).]
persistent spatial and temporal identity is realized through the recursive reactions that generate the components that re-produce the system, including the boundary that separates it from the external environment (for example, a membrane). This idea of an autopoietic system, introduced shortly after the publication of Gánti's book, is a more abstract version of Gánti's explicitly chemical model of minimal life. In his chemoton system, Gánti showed how the three coupled autocatalytic subsystems (the autocatalytic abcde cycle, the membrane subsystem, and the information polymer cyclical subsystem) that form the unified chemoton system generate a minimal living system (Fig. 1). The autocatalytic subsystem uses substances from the external environment, transforms them into components for its own reproduction and for the production of the other two subsystems, and exudes waste materials. The membrane system incorporates, through self-assembly, components of the autocatalytic cycle into the membrane that forms the boundary between the chemoton and the external environment. The informational polymer system, which in this version of the chemoton is a linear double-stranded polymer grows and reproduces by the templatebased addition of other metabolic by-products (Maynard Smith and Szathmáry, 1995, p. 23). Template-based polymerization occurs only when the units that are components of the polymer reach a critical concentration: the original doubles-stranded
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polymer then separates into two single structures, and the polymer components are consumed as they join to form new double structures. When the membrane reaches a critical size, for physical reasons it becomes deformed, and this leads to fission, to reproduction. The chemoton satisfies Gánti's list of life-criteria: it metabolizes, is stable, there is simple regulation of its general size and rate of growth, it has a subsystem carrying information about the system as a whole, its system-properties are emergent (non-additive), and its destruction is irreversible (it is therefore “mortal”); the system also grows and multiplies, and displays heredity; finally, chemotons can heritably vary – they can have different chemical metabolic cycles leading to different rates of production of components, or to chemically different membrane components that affect the timing of fission, or to differentlength linear polymers – and hence, selection among them is inevitable. The most important source of hereditary variation in the chemoton is the length of the linear polymer, because this is the only subsystem in which variation involves only a change in organization and control (Gánti, 2003, p. 44; Maynard Smith and Szathmáry, 1995, p. 23). Variations in the length of the polymer that occur during its replication would allow several hereditary variants differing in growth rates, whereas variations in the chemical cycle and membrane components would be more constrained by the special reactions carried out through these subsystems. Gánti showed that the constraints that limit heritable variability in the model shown in Fig. 1 are overcome if the linear polymer is made up of two types of units rather than one, and it is its sequence, rather than its length, that controls reproduction. In principle, with two polymer units, the variations among chemotons can be practically unlimited, allowing open-ended evolution. “Unlimited” is to be understood not in the mathematical sense, but as unlimited with regard to the number of different types of individuals in the population. Maynard Smith and Szathmáry (1995) took up, generalized and sharpened Gánti's ideas about the importance of the capacity of a system to generate hereditary variation. They described systems that can have only very few hereditary variants as limited heredity systems. When the number of the hereditary variations in such systems becomes vast (practically unlimited) they become unlimited heredity systems; they are fully mature and unambiguously identifiable living systems. The transition from complex chemical systems to systems with the capacity for open-ended evolution that is conferred by unlimited heredity is implemented by a complex system of coupled reactions, something like an autopoietic chemoton system. It is the distinction between limited and unlimited heredity systems that enables the identification of systems that, although different from an extant mature living system, could have led to the transition to living. Such a system has the minimal properties necessary for it to be considered a minimal living system. Gánti was not a philosopher of biology, but since his chemoton model sheds light on the emergence of functional organization, it also sharpens our conceptualization of the notion of function. When a system becomes organized in a way that leads to its longterm self-maintenance, its parts and the processes it generates can be said to have functions. Biological function is defined as the role that a part, a process or a mechanism plays within an encompassing system, a role that contributes to the goal-directed behavior of that system (see discussion in Jablonka (2002)). Paradigmatic goaldirected systems are living beings that reconstruct themselves and their parts, systems designed by living creatures (e.g. human houses, termite mounds), and even parts and processes in much simpler autopoietic systems, including limited-heredity chemotons that reside in the gray area between chemistry and biology (Keller, 2011). The most basic goal-directed behavior of living organisms is self-maintenance (survival) and, in the long-term, reproduction. Function is therefore not a new high-level chemical
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process or trait. In Aristotelian terms, it is an attribute of a teleological system, of a system that can be described in terms of a goal, “that for the sake of which” it exists.
3. Minimal consciousness and its evolutionary origins While the nature of minimal life and the origin of life are considered to be very difficult but fully scientific questions (Fry, 2000), the problem of the nature and origin of consciousness or subjective experiencing – the ability to feel, perceive and think rather than merely to process information – is regarded by some philosophers as a problem that defies current scientific approaches. In his article “What is it like to be a bat?” Thomas Nagel discussed the subjective experiencing of species that perceive the world in ways different from ours (such as a bat navigating using sonar), and pointed to our inability to have subjective understanding of the bat's consciousness through a detailed, third-person scientific knowledge of the bat's neural mechanisms (Nagel, 1974). Joseph Levine accepted Nagel's point, claiming that there is an explanatory (epistemological) gap between mechanisms and functions on one hand, and subjective experiencing on the other (Levine, 1983). David Chalmers called bridging this explanatory gap the “hard problem” of consciousness, and suggested that consciousness needs to be explained in terms of a new physical primitive (like mass or electric charge) which would render a theory of consciousness more similar to elegant physics than to “messy biology” (Chalmers, 1995, 1997). In a recent book, Nagel extended his initial position, claiming that the failure of science to account for consciousness renders the current, generally accepted theory of evolution questionable: not only the evolution of consciousness, but also the evolution of life and of complex adaptations like the genetic code cannot, he claimed, be explained by existing materialist evolutionary theory. This supposed failure suggested to Nagel that basic physics is in dire need of foundational enrichment. To fully explain the appearance of mentality, life and human reason, Nagel argued that one has to assume intrinsic mentality that pervades all matter, in conjunction with a teleological law of nature (Nagel, 2012). Although Nagel's position is not the majority view among philosophers of mind (for a critique see Jablonka and Ginsburg (2013)), it does reflect a general dissatisfaction with current naturalistic-evolutionary notions of consciousness. We believe that a fruitful alternative view may emerge if the approach Gánti used to the problem of the origin of life is applied to the problem of the origin of consciousness. If we think in terms of minimal consciousness, several components of the Gántian approach are already in place, and putting them together should indicate the kind of work that needs to be done for consciousness studies to progress. We first look at lists of characteristics of consciousness compiled by philosophers and neuroscientists, and give an example of a scheme describing the dynamics sketched by a neuroscientist, which is based on mammalian nervous systems. We then suggest a transition marker that characterizes biologically conscious organisms and an evolutionary scenario that is based on this notion. Table 2 compares three lists of attributes of basic consciousness (the basic ability to perceive and feel). The first list is compiled from philosophical analyses; the second list is extracted from the studies of leading neurobiologists, and the third (right column) by one particular neuroscientist, Edelman (2003), who more than a decade ago offered a detailed list of the characteristics of mental states. There are, of course, many differences among the opinions of the scholars from whose detailed studies Table 2 has been extracted, just as there are important differences of opinion among the origin-of-life researchers listed in Table 1. Our purpose here, as in the previous section, is to highlight the many overlaps and similarities among the
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Table 2 Lists of defining characteristics of basic consciousness. a
Characteristics of mental states
Mental states according to philosophers
Subjective experiences, values
Include subjective feelings, perception, thoughts, Values, emotions and goals evaluations and moods
Mental states according to neurobiologists
b
Unity, diversity Diverse yet unified states, with a qualitative and Self “feel”; felt as “owned” by the subject, leading to the feeling that there is a unified owner, a “self”
Global activity and dynamically changing and differentiated brain states. Binding and unification, leading to both specific qualitatively distinct experiences and an experience of “self”
Attentional modulation Gestalt, plasticity and temporal thickness Selection Intentionality, transparency
Modulated by attention
Attentional modulation
Characterized by spatial and temporal gestalt structures that organize perception and affect into qualitatively distinct spatial wholes, having temporal “thickness”, or presentness
Show plasticity, metaplasticity and temporal thickness
Embodiment and situatedness
Involve selection dynamics in the brain Involve neural selection processes Intentional [they are about something, directed Are goal directed towards objects and state of affairs]; refer to and project the effects of neurophysiological states onto internal bodily states and onto the external world, leading to the “transparency” of the world and the naïve self-evidence of the self Are embodied and situated Depend on the dynamic organization of the embodied nervous system
Mental states according to Edelman (2003)
Reflect subjective feelings, qualia, phenomenality, mood, pleasure, and unpleasure. Give rise to feelings of familiarity or its lack Are unitary, integrated, and constructed by the brain. They can be enormously diverse and differentiated; are temporally ordered, serial, and changeable. Reflect a binding of diverse modalities Subject to attentional modulation, from focal to diffuse Have constructive properties: gestalt, closure, and the phenomena of filling in. Have widespread access and associativity. Have center periphery, surround, and fringe aspects Neural Darwinism processes are involved Show intentionality with wide-ranging contents
Are concerned with situatedness and placement in the world
a Based on the views of Block (2007), Churchland (1989), Churchland (2002), Clark (2008), Dennett (1991), Gallagher and Zahavi (2012), Metzinger (2009), Searle (2004) and Thompson (2007). Humphrey (2011), a psychologist, and Hofstadter (2007), a cognitive scientist, are included because they have discussed these characteristics from a philosophical point of view. b Based on Crick and Koch (2003), Damasio (1999, 2010), Dehaene et al. (1998), Edelman and Tononi (2000), Freeman (1991) and Llinas et al. (1998).
lists of characteristics of consciousness. Any viable model of consciousness must not only be compatible with these defining features, it must also presuppose them (Bronfman, Ginsburg and Jablonka, submitted). Just as the chemoton model embodies and instantiates all the criteria in Gánti's list (and in the inventories of others), a good model of minimal consciousness would instantiate the defining characteristics outlined in Table 2. At present there is no conceptual–biological model of minimal consciousness equivalent to the Gántian model of minimal life. Existing neurophysiological models describe important interactions that conscious systems exhibit, such as recurrent back-andforth interactions between neuronal groups, multiple feedbacks, and both top-down and bottom-up relations between different brain regions, but they do not generate or instantiate the defining features of consciousness, such as subjectivity or transparency. Fig. 2 shows an example of a schematic model by the neurobiologist Freeman that depicts some salient features of consciousness; it was constructed on the basis of his studies of perception in mammals, especially olfactory perception in rabbits (Freeman, 2000). We chose this scheme because it includes not only the brain but also the rest of the body and the environment. Freeman's “intentional arc”, like the “dynamic core” of Edelman and Tononi (2000), and the “global workspace” of Baars (1997) and Dehaene et al. (1998), captures some features of the dynamic interactions that occur during the generation of consciousness. However, like all schemes for describing consciousness dynamics, it too fails to instantiate sentience (minimal consciousness), and does not go beyond a re-description of some of the necessary conditions for its occurrence. Why does it fail? Is the reason empirical, the result of the scarcity of relevant data? Is it the result of the type of model chosen (e.g. a static two-dimensional network rather than a robot)? Or is it, as we suggest, conceptual, due to the lack of a systematically explored scheme of minimal consciousness?
Body
Sensory Systems
Entorhinal Cortex
Motor Systems
Hippocampus
Receptors
Environment
Exploration
Fig. 2. Freeman's “Intentional Arc” (intentionality is the hallmark of consciousness in Freeman's opinion). Based on Freeman (2000, Fig. 2, p. 305).
Gánti's model of minimal life provided a conceptual framework for the analysis of living organization. Gánti showed how a system with the capacity for unlimited heredity and open-ended evolution fulfills all his criteria for life. It has to be organized as a highly complex system, which we call an “enabling system” that carries out the many processes that render unlimited heredity (the transition marker) possible (complex metabolic pathways, closure, high level of functional plasticity, and so on). A modern cell is clearly such an enabling system, and we can assume that it was preceded by precursor enabling-systems that occupied the gray area that preceded life as we know it. The idea that the unlimited heredity that confers the capacity for open-ended evolution is a marker of full blown life, emerged from Gánti's chemoton model, but it is a general criterion for life on earth, and can be applied to other models of minimal life (for example, an RNA network), and can even be derived from theoretical principles. Finding a
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comparable transition marker that characterizes basic consciousness and is compatible with existing neurophysiological data, would help to reveal how consciousness is constructed and point to the evolutionary trajectories leading to it. We suggest the transition marker that characterizes consciousness is unlimited associative learning (UAL), which evolved in animals from a state of limited learning. In animals with limited learning, most learning is non-associative, mainly learning by sensitization and habituation. When associations do form, the number of relations between different stimuli and between stimuli and responses that can be learned and recalled during the lifetime of an animal is very small. Consequently, the number of sensory categorizations that can be assigned a value that the animal is capable of forming is also small. In contrast, with UAL the number of associations between features of objects and between motor action and reinforcements that can be learned and recalled within and between modalities during the ontogeny of an individual far exceeds those that actually form during its lifetime, and also far exceeds the number of individuals in a population (for an operational definition that presupposes the list and the existing models see Bronfman, Ginsburg and Jablonka, submitted; for examples of compound associative learning in invertebrates see Perry et al., 2013). There are, of course, many constraints on UAL in any learning animal (including humans), but nevertheless, the number of possible learned associations is vast, and learningbased plasticity is never fully exhausted. In animals capable of UAL, sensory categorization is both rich and persistent, and the integrated sensory states that are generated act as internal guides and selectors of new neural relations, new actions, and new ends. For UAL to exist, animals need to have a sophisticated enabling system: a central nervous system, a highly innervated body integrated at different levels, multiple feedback relations between sensory categorization programs, exploratory motor programs, and flexible values systems (for more detailed arguments see Ginsburg and Jablonka, 2007a, 2007b, 2010a; Perry et al., 2013). In fact, UAL presupposes a complex enabling system having all the characteristics suggested as crucial for conscious activity (Bronfman, Ginsburg and Jablonka, submitted). We need to stress that just as unlimited heredity is not synonymous with life, but is a marker of organic-chemistry-based life in evolved complex biological systems, so too UAL is not equivalent to consciousness. It is, we suggest, a reliable marker, an indicator of recognizable consciousness in evolved animals. As with the transition to life, we assume that there is a large gray area that defies clear definition, which, in the case of the transition to consciousness, is inhabited by animals with limited learning. Once a transition marker for consciousness is defined, evolutionary scenarios can be suggested and evolutionary questions can begin to be addressed: what were the necessary building blocks that enabled the transition to full blown UAL? When did it originate? What were the ecological contexts in which it occurred? If the presence of UAL is taken as a reliable marker of consciousness, the evolution of UAL becomes fundamental to consciousness studies. Since the molecular correlates of learning (specific synaptic proteins and epigenetic regulatory factors) are far easier to pinpoint than the molecular correlates of consciousness, the evolution of UAL can be followed and the evolutionary transition to UAL can be tracked by using the comparative method. We have suggested that associative learning (AL) that led to UAL evolved during the Cambrian in several animal groups in parallel, and that it drove the great evolutionary diversification that occurred during this period. Once AL appeared on the evolutionary scene, it enabled animals to exploit new niches and promoted new types of relations among them, leading to adaptive responses and new morphologies that became fixed through genetic accommodation processes (Ginsburg and Jablonka, 2010b).
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We believe that a Gántian approach provides a conceptual framework for studying consciousness, opening up new avenues in the study of biological enigmas such as the evolution of consciousness and helping to disentangle thorny conceptual issues in the philosophy of mind. In his famous argument for granting consciousness a special status, David Chalmers maintained that the problem of consciousness is very different from the problem of life, which he agreed is amenable to standard materialistic evolutionary explanations in terms of specific functions and adaptations. With life, says Chalmers, all one needs to do is to explain functions such as reproduction, metabolism and the way that the system self-organizes (1997, p. 6), but in the case of consciousness, a list of the functions (e.g. decision making, attention focusing) and structures related to it is insufficient. With consciousness, he argued, the question about why having these functions entails the ability to experience (perceive, feel, think) remains. We agree with Chalmers's argument that explanations in terms of adaptive operational functions alone are not sufficient for explaining consciousness, but we think that he is wrong in assuming that consciousness (subjective experiencing) is a new high-level biological trait. Just as life is not a merely new high-level chemical process or trait but rather a reproductive teleological system, and just as the function of a part or a process is an attribute entailed by a goal-directed system, so consciousness should be seen as a new teleological system, the teloi of which are the fulfillments of feelings, needs and desires (Jablonka and Ginsburg, 2013). Subjectively felt experiences are entailed by this teleological system, just as functions are entailed by a living system. We agree with Chalmers' claim that we need a new theory, or a new theoretical framework that can enable us to figure out how subjective experiencing can emerge from certain biological functions, structures and mechanisms. But we think that the required theory is more like Gánti's chemoton theory (linked to a sophisticated evolutionary account) than a new theory of fundamental physics, as Chalmers suggested. As we hope to have shown, Gánti's approach to life is an inspiring heuristic that can be used for the systematic study of one of the great challenges for the 21st century biologists. Although we have not discussed it here, the same heuristic can be applied to the structure and evolution of human reasoning and human symbolic values, where the system is the social–cultural system in which humans are embedded, and the transition marker for it is unlimited symbolic representation and communication that lead to open-ended cultural evolution. An analysis of human culture and its biological enabling conditions is part of an ongoing research program in many disciplines in the biological and social sciences today. We would like to end by drawing attention to Gánti's call for the creation of theoretical biology, which can provide models of biological entities and, as he noted at the end of his book, should be driven by human responsibility (Gánti, 1987, p. 191). This call is even more urgent if we include in our theoretical biology the study of consciousness and of human values.
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Ginsburg, S., Jablonka, E., 2010a. Experiencing: a Jamesian approach. J. Conscious. Stud. 17, 102–124. Ginsburg, S., Jablonka, E., 2010b. The evolution of associative learning: a factor in the Cambrian explosion. J. Theor. Biol. 266, 11–20. Hofstadter, D.R., 2007. I Am a Strange Loop. Basic Books, New York. Humphrey, N., 2011. Soul Dust: The Magic of Consciousness. Princeton University Press, Princeton, NJ. Jablonka, E., 2002. Information: its interpretation, its inheritance and its sharing. Philos. Sci. 69, 578–605. Jablonka, E, Ginsburg, S., 2013. The major teleological transitions in evolution: why the materialistic evolutionary conception of nature is almost certainly right. J. Conscious. Stud. 20 (9–10), 177–189. Jablonka, E., Lamb, M.J., 2006. The evolution of information in the major transitions. J. Theor. Biol. 239, 236–246. Keller, E.F., 2011. Self-organization, self-assembly, and the inherent activity of matter. In: Gissis, S.B., Jablonka, E. (Eds.), Transformations of Lamarckism: from Subtle Fluids to Molecular Biology. MIT Press, Cambridge, MA, pp. 357–364. Lamarck, J.B., 1809. Philosophie Zoologique. Hafner, New York (Translated into English as Zoological philosophy by H. Elliot in 1914). Levine, J., 1983. Materialism and qualia: the explanatory gap. Pac. Philos. Q. 64, 354–361. Llinas, R., Ribary, U., Contreras, D., Pedroarena, C., 1998. The neuronal basis for consciousness. Philos. Trans. R. Soc. Lond. B 353, 1841–1849. Maturana, H., Varela, F., 1973. Boston studies in the philosophy of science. In: Cohen, R.S., Wartofsky, M.W. (Eds.), Autopoiesis and Cognition: The Realization of the Living, 42. D. Reidel Publishing Co., Dordecht, Holland. Maynard Smith, J., Szathmáry, E., 1995. The Major Transitions in Evolution. Oxford University Press, Oxford, UK. Mayr, E., 1982. The Growth of Biological Thought. Harvard University Press, Cambridge, MA. Metzinger, T., 2009. The Ego Tunnel The Science of the Mind and the Myth of the Self. Basic Books, New York. Nagel, T., 1974. What is it like to be a bat? Philos. Rev. LXXXIII 4, 435–450. Nagel, T., 2012. Mind and Cosmos. Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False. Oxford University Press, New York. Orgel, L.E., 1973. The Origins of Life: Molecules and Natural Selection. John Wiley & Sons, New York. Perry, C.J., Barron, A.B., Cheng, K., 2013. Invertebrate learning and cognition: relating phenomena to neural substrate. WIRE Cogn. Sci. 4 (5), 561–582. Searle, J., 2004. Mind: A Brief Introduction. Oxford University Press, New York. Thompson, E., 2007. Mind in Life: Biology, Phenomenology, and the Science of Mind. Harvard University Press, Cambridge, MA.
Contents lists available at ScienceDirect
Journal of Theoretical Biology journal homepage: www.elsevier.com/locate/yjtbi
The teleological transitions in evolution: A Gántian view Simona Ginsburg a, Eva Jablonka b,n a b
Natural Science Department, The Open University of Israel, Raanana 43107, Israel The Cohn Institute for the History and Philosophy of Science and Ideas, Tel-Aviv University, Tel-Aviv 69978, Israel
H I G H L I G H T S
Approaching Aristotelian teleological systems from an evolutionary perspective. Describing Gánti's strategy for the study of minimal life. Discussing Gánti's transition marker for life: unlimited heredity. Applying Gánti's strategy to the evolutionary transition to minimal consciousness. Suggesting a transition marker for consciousness: unlimited associative learning.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 March 2015 Received in revised form 5 April 2015 Accepted 7 April 2015 Available online 15 April 2015
We discuss Gánti's approach to the study of minimal living organization, and suggest that his methodology can be applied to the study of the two other major teleological systems described by Aristotle: minimal consciousness (sentience, experiencing) and rationality. We start by outlining Gánti's strategy for the case of life: listing the basic characteristics that any living system capable of open-ended evolution must satisfy, developing a dynamic model that instantiates these characteristics (the chemoton), and identifying a capacity of the system (unlimited heredity) that allows the system to dynamically persist over evolutionary time and to be used as a marker of the evolutionary transition to life. We apply Gánti's explanatory strategy to the evolutionary transition to minimal consciousness, suggest a transition marker (unlimited associative learning) and discuss the wider evolutionary and philosophical implications of this approach. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Chemoton Consciousness Origin of life Transition marker
1. Introduction Gánti's contribution to the study of minimal life is now well recognized, and many of the papers in this issue show his longlasting influence on research in the fields of systems-chemistry and the origin of life. However, what we want to show is how Gánti's approach to the study of minimal-life can be extended and used more generally for studying the origins of the two other great teleological systems: basic animal consciousness (which is our focus here), and human rationality and symbolic values. The analysis of living systems in terms of their goal-directedness has deep roots in Western philosophy. In On the Soul, Aristotle carved the living world at its teleological joints and suggested that the “soul” (psyche) is a principle of living organization that has three hierarchically-ordered incarnations. The first and most basic, which is manifested even in plants, is the reproductive or nutritive soul,
n
Corresponding author. E-mail addresses: [email protected] (S. Ginsburg), [email protected] (E. Jablonka). http://dx.doi.org/10.1016/j.jtbi.2015.04.007 0022-5193/& 2015 Elsevier Ltd. All rights reserved.
which is characterized by growth and generation and has the goal of survival and reproduction. The second incarnation is the sensitive soul, the soul of animals, which is built on the nutritive one and is characterized by sensation, movement, desire and motivation (and in some animals also imagination); its teloi (goals) are the satisfaction of felt needs and passions. The third, the rational soul (in mortal humans), is built on the previous two, and is characterized by rational thinking and striving for abstract symbolic teloi: for moral and esthetic values like the good and the beautiful. One can look at these Aristotelian goal-directed systems from an evolutionary point of view, seeing their origins in terms of evolutionary transitions from one state to another. The transition to Aristotle's nutritive soul is the transition to the first living system(s), which is the research topic to which Gánti contributed most directly; although studying the origin of life from the inanimate still presents great challenges, it has ceased to be a conceptual mystery (at least to most scientists and many philosophers). The second transition is the transition to consciousness, the evolutionary origin of Aristotle's sensitive soul; its study is shrouded in more conceptual fog and is only just beginning to gain momentum. The third is the transition to rationalizing-symbolizing animals, to
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Table 1 Representative lists of characteristics of minimal living systems [Gánti's list is highlighted]. Author
Characteristics
Emphasis
Lamarck (1809)
1. Individuality; 2. Birth and development; 3. Special flux (electricity and caloric) dynamics; 4. Nutrition and controlled growth; 5. Manufacturing components of self; 6. Reproduction and multiplication; 7. Mortality 1. Inherent unity; 2. Metabolism; 3. Inherent stability; 4. Information-carrying sub-system; 5. Program control; 6. Growth and multiplication; 7. Hereditary system enabling open-ended evolution; 8. Mortality 1. Individuality (closure); 2. Self-production; 3. Responsiveness; 4. Regulation and selectivity
Self-organization, metabolism Self-organization; evolution Metabolism, autopoeisis
1. Functionally complex organization; 2. Natural selection can occur; 3. Replication of a genetic material; 4. Information for specifying the living system stored in stable chemical molecules 1. Complexity and organization; 2. Chemical uniqueness (living organisms are composed of large polymers); 3. Quality (some relations between aspects of the living world can only be described qualitatively); 4. Uniqueness and variability; 5. Possession of a genetic program; 6. Historical nature; 7. Natural selection can occur; 8. Indeterminacy (biological systems have emergent properties) 1. Manufacturing its own constituents; 2. Extracting energy and converting it to work for the system; 3. Catalyzing system's reactions; 4. Having information systems enabling re-production; 5. Closure (individuality); 6. Regulation; 7. Multiplication 1. Self-organization; 2. Autonomy; 3. Emergence; 4. Development; 5. Adaptation; 6. Responsiveness; 7. Evolution; 8. Reproduction, growth; 9. Metabolism
Information, evolution
Gánti (1971, 1987) Maturana and Varela (1973) Orgel (1973) Mayr (1982)
De Duve (1991)
Boden (2009)
Evolution
Metabolism
Information, autopoiesis, evolution
Aristotle's rational (human) soul; this is one of the hottest topics in present-day evolutionary-cognitive biology, although its study goes all the way back to Darwin. Although all of Aristotle's goal-directed systems are the products of chemical and biological evolution, the way they are organized and how they evolved are major questions for evolutionary biologists and philosophers. To show how the way in which Gánti approached the study of living organization has not only shed light on the transition to life but can also provide a framework for understanding other teleological transitions, we start by outlining Gánti's strategy in accounting for living organization. We then show how adopting this strategy can shed light on the study of animal consciousness.
2. Gánti's strategy: the list, the dynamics, and the transition marker In his seminal book, The Principle of Life, Gánti (1971, 1987) described his chemical model of minimal life. He started by listing the basic characteristics that any living system capable of openended evolution must satisfy. As Table 1 shows, his list in many ways is similar to those of others. However, Gánti's major interest was not to characterize life in the abstract, but to describe the minimal system that can instantiate the formal and functional properties of life on earth. Gánti constructed an abstract chemical dynamical model, the chemoton (Fig. 1), which instantiated the eight criteria of life that he considered to be essential; five of them (1–5) are “absolute”, in the sense that life cannot exist without them; and three of them (6–8) are “potential”, which means that living forms having these properties can undergo open-ended evolution leading to the emergence of extant, complex, life forms. The ability to generate the vast number of hereditary variations on which the capacity for open-ended evolution rests is the hallmark of all the forms of life we know, and depends on all the other criteria in Ganti's list. It is what we call the transition marker for life. Although not himself involved in prebiotic geochemistry research, Gánti suggested that his list of criteria and his chemoton model could be used to constrain and guide the construction of concrete, geochemicallyinformed scenarios of the early processes on earth that led from chemistry to biology. In spite of the many questions left open by the chemoton model [discussed by Griesemer and Szathmáry in their commentaries on the later edition of Gánti's book (Gánti, 2003)], in the decades since it was constructed it has proved to be a useful guide for theoretical and empirical approaches to the origin of life (see papers in this issue). It is an example of what Maturana and Varela (1973) called an autopoietic system: a system whose
Fig. 1. Gánti's chemoton is made up of three tightly coupled subsystems: the autocatalytic metabolic cycle (abcde cycle), the informational cycle that generates the polymer, and the membrane-forming subsystems. [Based on Gánti, 2003, Fig. 1.1, p. 4), Maynard Smith and Szathmáry (1995, p. 20–23) and the modification of this figure in Jablonka and Lamb (2006, Fig 1, p. 237).]
persistent spatial and temporal identity is realized through the recursive reactions that generate the components that re-produce the system, including the boundary that separates it from the external environment (for example, a membrane). This idea of an autopoietic system, introduced shortly after the publication of Gánti's book, is a more abstract version of Gánti's explicitly chemical model of minimal life. In his chemoton system, Gánti showed how the three coupled autocatalytic subsystems (the autocatalytic abcde cycle, the membrane subsystem, and the information polymer cyclical subsystem) that form the unified chemoton system generate a minimal living system (Fig. 1). The autocatalytic subsystem uses substances from the external environment, transforms them into components for its own reproduction and for the production of the other two subsystems, and exudes waste materials. The membrane system incorporates, through self-assembly, components of the autocatalytic cycle into the membrane that forms the boundary between the chemoton and the external environment. The informational polymer system, which in this version of the chemoton is a linear double-stranded polymer grows and reproduces by the templatebased addition of other metabolic by-products (Maynard Smith and Szathmáry, 1995, p. 23). Template-based polymerization occurs only when the units that are components of the polymer reach a critical concentration: the original doubles-stranded
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polymer then separates into two single structures, and the polymer components are consumed as they join to form new double structures. When the membrane reaches a critical size, for physical reasons it becomes deformed, and this leads to fission, to reproduction. The chemoton satisfies Gánti's list of life-criteria: it metabolizes, is stable, there is simple regulation of its general size and rate of growth, it has a subsystem carrying information about the system as a whole, its system-properties are emergent (non-additive), and its destruction is irreversible (it is therefore “mortal”); the system also grows and multiplies, and displays heredity; finally, chemotons can heritably vary – they can have different chemical metabolic cycles leading to different rates of production of components, or to chemically different membrane components that affect the timing of fission, or to differentlength linear polymers – and hence, selection among them is inevitable. The most important source of hereditary variation in the chemoton is the length of the linear polymer, because this is the only subsystem in which variation involves only a change in organization and control (Gánti, 2003, p. 44; Maynard Smith and Szathmáry, 1995, p. 23). Variations in the length of the polymer that occur during its replication would allow several hereditary variants differing in growth rates, whereas variations in the chemical cycle and membrane components would be more constrained by the special reactions carried out through these subsystems. Gánti showed that the constraints that limit heritable variability in the model shown in Fig. 1 are overcome if the linear polymer is made up of two types of units rather than one, and it is its sequence, rather than its length, that controls reproduction. In principle, with two polymer units, the variations among chemotons can be practically unlimited, allowing open-ended evolution. “Unlimited” is to be understood not in the mathematical sense, but as unlimited with regard to the number of different types of individuals in the population. Maynard Smith and Szathmáry (1995) took up, generalized and sharpened Gánti's ideas about the importance of the capacity of a system to generate hereditary variation. They described systems that can have only very few hereditary variants as limited heredity systems. When the number of the hereditary variations in such systems becomes vast (practically unlimited) they become unlimited heredity systems; they are fully mature and unambiguously identifiable living systems. The transition from complex chemical systems to systems with the capacity for open-ended evolution that is conferred by unlimited heredity is implemented by a complex system of coupled reactions, something like an autopoietic chemoton system. It is the distinction between limited and unlimited heredity systems that enables the identification of systems that, although different from an extant mature living system, could have led to the transition to living. Such a system has the minimal properties necessary for it to be considered a minimal living system. Gánti was not a philosopher of biology, but since his chemoton model sheds light on the emergence of functional organization, it also sharpens our conceptualization of the notion of function. When a system becomes organized in a way that leads to its longterm self-maintenance, its parts and the processes it generates can be said to have functions. Biological function is defined as the role that a part, a process or a mechanism plays within an encompassing system, a role that contributes to the goal-directed behavior of that system (see discussion in Jablonka (2002)). Paradigmatic goaldirected systems are living beings that reconstruct themselves and their parts, systems designed by living creatures (e.g. human houses, termite mounds), and even parts and processes in much simpler autopoietic systems, including limited-heredity chemotons that reside in the gray area between chemistry and biology (Keller, 2011). The most basic goal-directed behavior of living organisms is self-maintenance (survival) and, in the long-term, reproduction. Function is therefore not a new high-level chemical
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process or trait. In Aristotelian terms, it is an attribute of a teleological system, of a system that can be described in terms of a goal, “that for the sake of which” it exists.
3. Minimal consciousness and its evolutionary origins While the nature of minimal life and the origin of life are considered to be very difficult but fully scientific questions (Fry, 2000), the problem of the nature and origin of consciousness or subjective experiencing – the ability to feel, perceive and think rather than merely to process information – is regarded by some philosophers as a problem that defies current scientific approaches. In his article “What is it like to be a bat?” Thomas Nagel discussed the subjective experiencing of species that perceive the world in ways different from ours (such as a bat navigating using sonar), and pointed to our inability to have subjective understanding of the bat's consciousness through a detailed, third-person scientific knowledge of the bat's neural mechanisms (Nagel, 1974). Joseph Levine accepted Nagel's point, claiming that there is an explanatory (epistemological) gap between mechanisms and functions on one hand, and subjective experiencing on the other (Levine, 1983). David Chalmers called bridging this explanatory gap the “hard problem” of consciousness, and suggested that consciousness needs to be explained in terms of a new physical primitive (like mass or electric charge) which would render a theory of consciousness more similar to elegant physics than to “messy biology” (Chalmers, 1995, 1997). In a recent book, Nagel extended his initial position, claiming that the failure of science to account for consciousness renders the current, generally accepted theory of evolution questionable: not only the evolution of consciousness, but also the evolution of life and of complex adaptations like the genetic code cannot, he claimed, be explained by existing materialist evolutionary theory. This supposed failure suggested to Nagel that basic physics is in dire need of foundational enrichment. To fully explain the appearance of mentality, life and human reason, Nagel argued that one has to assume intrinsic mentality that pervades all matter, in conjunction with a teleological law of nature (Nagel, 2012). Although Nagel's position is not the majority view among philosophers of mind (for a critique see Jablonka and Ginsburg (2013)), it does reflect a general dissatisfaction with current naturalistic-evolutionary notions of consciousness. We believe that a fruitful alternative view may emerge if the approach Gánti used to the problem of the origin of life is applied to the problem of the origin of consciousness. If we think in terms of minimal consciousness, several components of the Gántian approach are already in place, and putting them together should indicate the kind of work that needs to be done for consciousness studies to progress. We first look at lists of characteristics of consciousness compiled by philosophers and neuroscientists, and give an example of a scheme describing the dynamics sketched by a neuroscientist, which is based on mammalian nervous systems. We then suggest a transition marker that characterizes biologically conscious organisms and an evolutionary scenario that is based on this notion. Table 2 compares three lists of attributes of basic consciousness (the basic ability to perceive and feel). The first list is compiled from philosophical analyses; the second list is extracted from the studies of leading neurobiologists, and the third (right column) by one particular neuroscientist, Edelman (2003), who more than a decade ago offered a detailed list of the characteristics of mental states. There are, of course, many differences among the opinions of the scholars from whose detailed studies Table 2 has been extracted, just as there are important differences of opinion among the origin-of-life researchers listed in Table 1. Our purpose here, as in the previous section, is to highlight the many overlaps and similarities among the
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Table 2 Lists of defining characteristics of basic consciousness. a
Characteristics of mental states
Mental states according to philosophers
Subjective experiences, values
Include subjective feelings, perception, thoughts, Values, emotions and goals evaluations and moods
Mental states according to neurobiologists
b
Unity, diversity Diverse yet unified states, with a qualitative and Self “feel”; felt as “owned” by the subject, leading to the feeling that there is a unified owner, a “self”
Global activity and dynamically changing and differentiated brain states. Binding and unification, leading to both specific qualitatively distinct experiences and an experience of “self”
Attentional modulation Gestalt, plasticity and temporal thickness Selection Intentionality, transparency
Modulated by attention
Attentional modulation
Characterized by spatial and temporal gestalt structures that organize perception and affect into qualitatively distinct spatial wholes, having temporal “thickness”, or presentness
Show plasticity, metaplasticity and temporal thickness
Embodiment and situatedness
Involve selection dynamics in the brain Involve neural selection processes Intentional [they are about something, directed Are goal directed towards objects and state of affairs]; refer to and project the effects of neurophysiological states onto internal bodily states and onto the external world, leading to the “transparency” of the world and the naïve self-evidence of the self Are embodied and situated Depend on the dynamic organization of the embodied nervous system
Mental states according to Edelman (2003)
Reflect subjective feelings, qualia, phenomenality, mood, pleasure, and unpleasure. Give rise to feelings of familiarity or its lack Are unitary, integrated, and constructed by the brain. They can be enormously diverse and differentiated; are temporally ordered, serial, and changeable. Reflect a binding of diverse modalities Subject to attentional modulation, from focal to diffuse Have constructive properties: gestalt, closure, and the phenomena of filling in. Have widespread access and associativity. Have center periphery, surround, and fringe aspects Neural Darwinism processes are involved Show intentionality with wide-ranging contents
Are concerned with situatedness and placement in the world
a Based on the views of Block (2007), Churchland (1989), Churchland (2002), Clark (2008), Dennett (1991), Gallagher and Zahavi (2012), Metzinger (2009), Searle (2004) and Thompson (2007). Humphrey (2011), a psychologist, and Hofstadter (2007), a cognitive scientist, are included because they have discussed these characteristics from a philosophical point of view. b Based on Crick and Koch (2003), Damasio (1999, 2010), Dehaene et al. (1998), Edelman and Tononi (2000), Freeman (1991) and Llinas et al. (1998).
lists of characteristics of consciousness. Any viable model of consciousness must not only be compatible with these defining features, it must also presuppose them (Bronfman, Ginsburg and Jablonka, submitted). Just as the chemoton model embodies and instantiates all the criteria in Gánti's list (and in the inventories of others), a good model of minimal consciousness would instantiate the defining characteristics outlined in Table 2. At present there is no conceptual–biological model of minimal consciousness equivalent to the Gántian model of minimal life. Existing neurophysiological models describe important interactions that conscious systems exhibit, such as recurrent back-andforth interactions between neuronal groups, multiple feedbacks, and both top-down and bottom-up relations between different brain regions, but they do not generate or instantiate the defining features of consciousness, such as subjectivity or transparency. Fig. 2 shows an example of a schematic model by the neurobiologist Freeman that depicts some salient features of consciousness; it was constructed on the basis of his studies of perception in mammals, especially olfactory perception in rabbits (Freeman, 2000). We chose this scheme because it includes not only the brain but also the rest of the body and the environment. Freeman's “intentional arc”, like the “dynamic core” of Edelman and Tononi (2000), and the “global workspace” of Baars (1997) and Dehaene et al. (1998), captures some features of the dynamic interactions that occur during the generation of consciousness. However, like all schemes for describing consciousness dynamics, it too fails to instantiate sentience (minimal consciousness), and does not go beyond a re-description of some of the necessary conditions for its occurrence. Why does it fail? Is the reason empirical, the result of the scarcity of relevant data? Is it the result of the type of model chosen (e.g. a static two-dimensional network rather than a robot)? Or is it, as we suggest, conceptual, due to the lack of a systematically explored scheme of minimal consciousness?
Body
Sensory Systems
Entorhinal Cortex
Motor Systems
Hippocampus
Receptors
Environment
Exploration
Fig. 2. Freeman's “Intentional Arc” (intentionality is the hallmark of consciousness in Freeman's opinion). Based on Freeman (2000, Fig. 2, p. 305).
Gánti's model of minimal life provided a conceptual framework for the analysis of living organization. Gánti showed how a system with the capacity for unlimited heredity and open-ended evolution fulfills all his criteria for life. It has to be organized as a highly complex system, which we call an “enabling system” that carries out the many processes that render unlimited heredity (the transition marker) possible (complex metabolic pathways, closure, high level of functional plasticity, and so on). A modern cell is clearly such an enabling system, and we can assume that it was preceded by precursor enabling-systems that occupied the gray area that preceded life as we know it. The idea that the unlimited heredity that confers the capacity for open-ended evolution is a marker of full blown life, emerged from Gánti's chemoton model, but it is a general criterion for life on earth, and can be applied to other models of minimal life (for example, an RNA network), and can even be derived from theoretical principles. Finding a
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comparable transition marker that characterizes basic consciousness and is compatible with existing neurophysiological data, would help to reveal how consciousness is constructed and point to the evolutionary trajectories leading to it. We suggest the transition marker that characterizes consciousness is unlimited associative learning (UAL), which evolved in animals from a state of limited learning. In animals with limited learning, most learning is non-associative, mainly learning by sensitization and habituation. When associations do form, the number of relations between different stimuli and between stimuli and responses that can be learned and recalled during the lifetime of an animal is very small. Consequently, the number of sensory categorizations that can be assigned a value that the animal is capable of forming is also small. In contrast, with UAL the number of associations between features of objects and between motor action and reinforcements that can be learned and recalled within and between modalities during the ontogeny of an individual far exceeds those that actually form during its lifetime, and also far exceeds the number of individuals in a population (for an operational definition that presupposes the list and the existing models see Bronfman, Ginsburg and Jablonka, submitted; for examples of compound associative learning in invertebrates see Perry et al., 2013). There are, of course, many constraints on UAL in any learning animal (including humans), but nevertheless, the number of possible learned associations is vast, and learningbased plasticity is never fully exhausted. In animals capable of UAL, sensory categorization is both rich and persistent, and the integrated sensory states that are generated act as internal guides and selectors of new neural relations, new actions, and new ends. For UAL to exist, animals need to have a sophisticated enabling system: a central nervous system, a highly innervated body integrated at different levels, multiple feedback relations between sensory categorization programs, exploratory motor programs, and flexible values systems (for more detailed arguments see Ginsburg and Jablonka, 2007a, 2007b, 2010a; Perry et al., 2013). In fact, UAL presupposes a complex enabling system having all the characteristics suggested as crucial for conscious activity (Bronfman, Ginsburg and Jablonka, submitted). We need to stress that just as unlimited heredity is not synonymous with life, but is a marker of organic-chemistry-based life in evolved complex biological systems, so too UAL is not equivalent to consciousness. It is, we suggest, a reliable marker, an indicator of recognizable consciousness in evolved animals. As with the transition to life, we assume that there is a large gray area that defies clear definition, which, in the case of the transition to consciousness, is inhabited by animals with limited learning. Once a transition marker for consciousness is defined, evolutionary scenarios can be suggested and evolutionary questions can begin to be addressed: what were the necessary building blocks that enabled the transition to full blown UAL? When did it originate? What were the ecological contexts in which it occurred? If the presence of UAL is taken as a reliable marker of consciousness, the evolution of UAL becomes fundamental to consciousness studies. Since the molecular correlates of learning (specific synaptic proteins and epigenetic regulatory factors) are far easier to pinpoint than the molecular correlates of consciousness, the evolution of UAL can be followed and the evolutionary transition to UAL can be tracked by using the comparative method. We have suggested that associative learning (AL) that led to UAL evolved during the Cambrian in several animal groups in parallel, and that it drove the great evolutionary diversification that occurred during this period. Once AL appeared on the evolutionary scene, it enabled animals to exploit new niches and promoted new types of relations among them, leading to adaptive responses and new morphologies that became fixed through genetic accommodation processes (Ginsburg and Jablonka, 2010b).
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We believe that a Gántian approach provides a conceptual framework for studying consciousness, opening up new avenues in the study of biological enigmas such as the evolution of consciousness and helping to disentangle thorny conceptual issues in the philosophy of mind. In his famous argument for granting consciousness a special status, David Chalmers maintained that the problem of consciousness is very different from the problem of life, which he agreed is amenable to standard materialistic evolutionary explanations in terms of specific functions and adaptations. With life, says Chalmers, all one needs to do is to explain functions such as reproduction, metabolism and the way that the system self-organizes (1997, p. 6), but in the case of consciousness, a list of the functions (e.g. decision making, attention focusing) and structures related to it is insufficient. With consciousness, he argued, the question about why having these functions entails the ability to experience (perceive, feel, think) remains. We agree with Chalmers's argument that explanations in terms of adaptive operational functions alone are not sufficient for explaining consciousness, but we think that he is wrong in assuming that consciousness (subjective experiencing) is a new high-level biological trait. Just as life is not a merely new high-level chemical process or trait but rather a reproductive teleological system, and just as the function of a part or a process is an attribute entailed by a goal-directed system, so consciousness should be seen as a new teleological system, the teloi of which are the fulfillments of feelings, needs and desires (Jablonka and Ginsburg, 2013). Subjectively felt experiences are entailed by this teleological system, just as functions are entailed by a living system. We agree with Chalmers' claim that we need a new theory, or a new theoretical framework that can enable us to figure out how subjective experiencing can emerge from certain biological functions, structures and mechanisms. But we think that the required theory is more like Gánti's chemoton theory (linked to a sophisticated evolutionary account) than a new theory of fundamental physics, as Chalmers suggested. As we hope to have shown, Gánti's approach to life is an inspiring heuristic that can be used for the systematic study of one of the great challenges for the 21st century biologists. Although we have not discussed it here, the same heuristic can be applied to the structure and evolution of human reasoning and human symbolic values, where the system is the social–cultural system in which humans are embedded, and the transition marker for it is unlimited symbolic representation and communication that lead to open-ended cultural evolution. An analysis of human culture and its biological enabling conditions is part of an ongoing research program in many disciplines in the biological and social sciences today. We would like to end by drawing attention to Gánti's call for the creation of theoretical biology, which can provide models of biological entities and, as he noted at the end of his book, should be driven by human responsibility (Gánti, 1987, p. 191). This call is even more urgent if we include in our theoretical biology the study of consciousness and of human values.
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