Piero Scaruffi

The Physics of Life (These are excerpts from, or extensions to, the material published in my book "The Nature of Consciousness") Life has three dimensions. One is the evolutionary dimension: living organisms evolve over time. One is the reproduction dimension: living organisms are capable of reproducing. One is the metabolic dimension: living organisms change shape during their life. Each dimension can be studied with the mathematical tools that Physics has traditionally employed to study matter. But it is apparent that traditional Physics cannot explain life. Life exhibits properties that rewrite Physics. The Origin Of Self-organization: life as negative entropy The paradox underlying natural selection (from the point of view of physicists) is that on one hand it proceeds in a blind and purpose-less way and on the other hand produces the illusion of more and more complex design. This continuous increase in information (i.e., the spontaneous emergence of order) seems to violate the second law of Thermodynamics, the law of entropy. Ludwig von Bertalanffy borrowed the term "anamorphosis" from the German biologist Richard Woltereck to describe the natural trend towards emergent forms of increasing complexity. Entropy is a measure of disorder and it can only increase, according to the second law of Thermodynamics. Information moves in the opposite direction. Most things in this universe, if left alone, simply decay and disintegrate. Biological systems, instead, appear from nowhere, then organize themselves, then even grow! This leads to the "two arrows of time": the behavior of inanimate matter pointing towards entropy increase and therefore disorder increase, and the behavior of biological systems pointing the other way by building increasingly complex structures of order. When you drop a sugar cube in your coffee, it dissolves: while no physical law forbids the recomposition of the sugar cube, in practice it never occurs, and we intuitively know that it cannot occur. Order is destroyed and cannot be recreated. That's a manifestation of the second law of Thermodynamics. On the other hand, a teenager develops into an adult, and, while no biological law forbids it, and as much as they would like to, adults never regress to youth. This is a manifestation of the opposite arrow of time: order is created and cannot be undone. Since organisms are made of chemicals, there is no reason why living systems should behave differently than inanimate systems. This is a paradox that puzzled not only biologists, but physicists too. The German physicist Ludwig von Boltzmann was possibly the first scientist to realize the importance of entropy for life. He reasoned that there is plenty of energy on Earth (air, water, minerals). Life is not driven by energy, or that would be no need for competition: life is driven by competition for entropy. Entropy (created by the transfer of energy from the hot Sun to the cold Earth) is much scarcer. The Austrian physicist Erwin Schroedinger, one of the founders of Quantum Mechanics, first proposed the idea that biological organization is created and maintained at the expense of thermodynamic order. Life displays two fundamental processes: creating order from order (the progeny has the same order as the parent) and creating order from disorder (as every living system does at every metabolic step, eating and growing). Living systems seem to defy the second law of Thermodynamics. In reality, they live in a world of energy flux that does not conform to the closed-world assumptions of Thermodynamics. An organism stays alive in its highly organized state by absorbing energy from the environment and processing it to produce a lower entropy state within itself. "Living organisms feed upon negative entropy": they attract "negative entropy" in order to compensate for the entropy increase they create by living. Life is "negentropic". The existence of a living organism depends on increasing the entropy of the rest of the universe. In 1974 the Hungarian biologist Albert Szent-Gyorgyi proposed to replace "negentropy" with the positive term "syntropy", so as to represent the "innate drive in living matter to perfect itself". This has a correspondent on the psychological level, "a drive towards synthesis, towards growth, towards wholeness and self-perfection". Life as Non-equilibrium In the 1960s, the Belgian (but Russian-born) physicist Ilya Prigogine (who would later be awarded the Nobel prize for his work in Thermodynamics) had a fundamental intuition: living organisms function as "dissipative structures" (a term first introduced by Ukrainian chemist Alfred Lotka). These are structures that form as patterns in the energy flow and that have the capacity for self-organization in the face of environmental fluctuations. In other words, they maintain their structure by continuously dissipating energy. Such dissipative structures reside permanently in states of non-equilibrium, unlike inanimate matter. Life maintains itself far from equilibrium: the form stays pretty much the same, while the material is constantly being replaced by new material, part of which comes from matter (food, air, water) and part of which comes from energy (sun). The flow of matter and energy "through" the body of the living organisms is what makes it possible for the organism to maintain a (relatively) stable form. In order to stay alive, they have to be always in this state far from equilibrium. Equilibrium is death, non-equilibrium is life. And here is the solution of the riddle. Equilibrium is the state of maximum entropy: uniform temperature and maximum disorder. A system that is not in equilibrium exhibits a variation of entropy which is the sum of the variations of entropy due to the internal source of entropy (which tends to increase towards equilibrium) plus the variation of entropy due to the interaction with the external world. The former is positive, but the latter can equally be negative. Therefore total entropy can decrease. An organism "lives" because it absorbs energy from the external world and processes it to generate an internal state of lower entropy. An organism "lives" as long as it can avoid falling in the equilibrium state. (In a sense, organisms die because this process is not perfect: if our bodies could be made to keep their shape exactly the same, they would always remain far from the equilibrium and they would never die). (But then there is a reason why it is not perfect and we have to die: a stable immutable form of life would have scant chances of surviving the continuous changes in the environment, whereas a form of life that continuously reshapes itself has a chance to "evolve" with the environment). Thanks to the advent of non-equilibrium Thermodynamics, it is now possible to bridge Thermodynamics and evolutionary Biology. By focusing on entropy, structure and information, it is now possible to shed some light on the relationship between cosmological evolution and biological evolution. Biological phenomena can be viewed as governed by laws that are purely physical. This step might prove as powerful as the synthetic theory of evolution. Prigogine’s non-equilibrium approach to evolution, i.e. that biological systems (from bacteria to entire ecological systems) are non-equilibrium systems, has become a powerful paradigm to study life in the context of Physics. Life can finally be reduced to a natural phenomenon just like electromagnetism and gravity. The Austrian physicist Erich Jansch has extended Prigogine’s vision of life to the entire universe: the universe as a gigantic self-organizing system subject to the laws of non-equilibrium thermodynamics. The American physicist Jeffrey Wicken went as far as to state that "Thermodynamics is above all the science of spontaneous processes", and link life with the expansion of the universe. Cycles Lotka pioneered the view of biological systems as endless cycles. Not only is a biological system a network of chemical agents (one chemical reaction leading to another one), but these agents somehow yield a cycling structure. The cycle helps the network exist, assume an identity and grow. This behavior is typical of life. Lotka called it "autocatalysis". Indirectly, Lotka was also one of the first scientists to show that biology was chemistry, and chemistry biology. Bioenergetics These ideas led to an approach to life, called "Bioenergetics", which consists in applying thermodynamic concepts (energy, temperature, entropy and information) and non-equilibrium (or irreversible) Thermodynamics to biological structures. The starting point, in the 1920s, was Lotka’s assumption that ecosystems are networks of energy flows. Then, decades later, the American brothers Howard and Eugene Odum devised a thermodynamic model for the development of the ecosystem. That became the route followed by an entire branch of Bioenergetics: looking for the thermodynamic principle that guides the development of ecosystems. Howard Odum, for example, coined the term "emergy" (for "embodied energy") to refer to the "energy memory" of living systems (a measure of energy used in the past). To him living systems had been formed by an accumulation of past energy, and thus were memories of all that energy. Eugene Odum viewed the entire Earth as a set of interconnected ecosystems. The American biologist Harold Morowitz held that the flow of energy through a living system acts to organize the system: organization emerges spontaneously whenever energy flows through a system. The contradiction between the second law of Thermodynamics (the universe tends towards increasing disorder) and biological evolution (life tends towards increasing organization) is only apparent, because Thermodynamics applies to systems that are approaching equilibrium (either adiabatic, i.e. isolated, or isothermal), whereas natural systems are usually subject to flows of energy/matter to or from other systems. First of all, life is the property of an ecological system, not of a single, individual, isolated organism. An isolated living organism is an oxymoron. Life of any organism depends on a flow of energy, and, ultimately, life "is" that flow of energy. Morowitz has proven two theorems that analyze what happens during that flow of energy through the chemical systems that living organisms are made of: 1. those systems store energy in chemical bonds, i.e. their complexity steadily increases; and 2. those systems undergo chemical cycles of the kind that pervade the biosphere (e.g., the carbon cycle). The flux of energy turns out to be the organizing factor in a dissipative system. When energy flows in a system from a higher kinetic temperature, the upper energy levels of the system become occupied and take a finite time to decay into thermal modes. During this period energy is stored at a higher free energy than at equilibrium state. Systems of complex structures can store large amounts of energy and achieve a high amount of internal order. The cyclic nature of dissipative systems allows them to develop stability and structure within themselves. The bottom line is that a dissipative system develops an internal order. Morowitz proved that Lotka was right: the flow of energy through a (steady state) system yields cycles, which in turn yield structure. The Evolution of Complex Systems American systems scientist James Kay and biologist Eric Schneider sided with Ilya Prigogine (and his distinguished predecessors Alfred Lotka and Erwin Schroedinger) in thinking that biological systems are the product of non-equilibrium thermodynamics, and indirectly the product of the second law of thermodynamics (that entropy can never decrease, unless there is a flow of energy). Living systems "emerge", or self-organize, and, de facto, it is inevitable that they emerged: it is written in the laws of physics. Non-equilibrium thermodynamics is the science of life. Thermodynamic equilibrium is death. Kay believes that there is more than a mere tendency towards creating life. He believes that life is a way to optimize and accelerate (not just carry out) the production of entropy mandated by the second law of Thermodynamics. Living systems are the most efficient way ever devised by Nature to destroy order; and never mind that living systems themselves appear to be among the most ordered systems ever created. It is all a trick to ultimately destroy order, just like warships are sophisticated complex buildings but overall their contribution to history was to destroy buildings. In 1965, American physicist Joseph Kestin proved that closed systems who are suddenly "freed" (i.e., their constraints are removed) tend to move towards a new state of equilibrium that is an "attractor". This state is called "attractor" because it does not depend on the order in which the constraints are removed: the system "has" to move towards that state. In other words, not only are some processes irreversible, but processes have a direction and an end. This is expressed by his "Unified Principle of Thermodynamics" (It is called "unified" because it really summarizes the other laws of Thermodynamics). Kay believes in a natural extension of this principle: a system pushed away from its attractor, will tend to return to the attractor. The stronger the push, the stronger the reaction, the reaction being some form of self-organization. When the gradient pushing the system is particularly strong, the system may self-organize in ever more complex structures. Thus Kay believes that nature will create complex systems whenever it can: it will use any means available to achieve equilibrium. The "actor" that pushes systems away from equilibrium is a gradient (a difference of temperature, pressure or other). Whenever a gradient is applied, the system is no longer in equilibrium. Kay believes that the reaction to a gradient is internal reorganization aimed at reducing and eventually neutralizing the external gradient. Gradient neutralization is a fundamental property of Thermodynamics, a fact already proven in 1993 by Don Mikulecky. "Exergy" is the amount of energy that one can extract from a system in the form of work. When the system has reached a condition of equilibrium, its exergy is zero. Exergy is thus also a measure of how far from equilibrium a system is. (An equivalent way of describing this phenomenon is to talk of "gradients", because the gradient is what can be used to generate work: heat, for example, can be turned into work because there is cold, otherwise it would be useless). temperature, for example, is what Living beings are non-equilibrium systems, so they have high exergy. Kay believes that the universal tendency towards equilibrium is driving evolution, that Nature is building more and more complex systems in order to erase exergy ever more efficiently. Living beings are only a cog in the machine built by Nature to destroy all exergy and achieve equilibrium. Life is only a way to break down concentrations of energy and turn it into diffuse waste heat. And we are an accidental by-product of such a universal process. Animals, for example, degrade the exergy of plants when they eat them. Furthermore, they do so in a way that is more efficient than other physical processes (burning the plant, for example, would radiate energy, while a cow eating grass radiates very little energy). In a sense, Nature created animals because they are the most efficient way to erase the exergy of plants, and it created plants because they are the most efficient way to erase the exergy of sunlight, and so on. Ecosystems have evolved from systems that emitted a lot of exergy to systems that emit little exergy. Metabolism is simply a way to degrade energy, and today's animals (such as mammals and birds) are a lot more efficient at it than the first forms of life. Evolution has been progressing towards more and more efficient systems to destroy exergy. Genetic information is simply information about how to destroy exergy. Ecosystems as a whole can also be viewed as efficient destroyers of gradients, destroyers that are built and driven by energy flows. The thermodynamic study of ecosystems carried out by Evelyn Hutchinson, Spanish biologist Ramon Margalef, Eugene Odum showed that ecosystems progress towards increased production of entropy and increased reduction of gradient (a different way of saying that biomass, species diversity and energy throughput all increase). The dynamics of ecosystems, in turn, drives evolution. It is the second law that selects the systems that are best at reducing gradients. Natural selection is, in a sense, an afterthought: the most important selection has already occurred, driven by the second law of thermodynamics. Darwin created a bridge between humans and other forms of life, and explained how one descended from the others. Kay and Schneider attempt to do something similar for living systems and non-living systems. Non-living complex systems play the same role that living systems play: they are just a bit less efficient. But they too are driven by the same phenomenon (ultimately, a "gradient"). The too spontaneously organize due to the energy flow caused by the gradient. Thus any non-living complex systems appears to be a predecessor of a living system. It is "born" and it "grows" and it "evolves" in a way similar to how life does, except that it is not alive (for example, it does not reproduce). Schneider summarized his universal principle as "Nature abhors gradients". Whenever there is a gradient, Nature responds by creating the most efficient way to erase it. One such efficient way is life, and us. In the end, the second law of Thermodynamics turns out to be responsible for both processes of living beings: both their growing and their decaying, both their non-equilibrium (peaking with progress and civilization) and their equilibrium (death). In the end, the purpose of life turns out to be death: Nature invented life on Earth as the most efficient process to reduces the gradient created by the Sun heating the Earth. The ultimate goal is to reestablish an equilibrium that will, incidentally, destroy all life when life will no longer needed to reduce a gradient that life will have erased. The meaning of life is, ultimately, suicide. The Origin of Biological Information A different but similar non-biological approach to life is based on information, and directly influenced by Cybernetics and Information Theory. Life is viewed as information capable of replicating and modifying itself. The American anthropologist Gregory Bateson believed that the substance of the biological world is "pattern" (not this or that chemical compost), a position that allowed him to seek a unified view of cognitive and biological (and cybernetic) phenomena. His definition of information stretched beyond mere computation: a bit of information is a difference that makes a difference. Thereby implying that, in order to be information, a pattern must affect something. (Also, information is not a thing, it is a relation). The pioneering work of the Spanish ecologist Ramon Margalef in the 1960's set the stage. He viewed an ecosystem as a cybernetic system driven by the second law of Thermodynamics. Succession (the process of replacing old species with new species in an ecosystem) is then a self-organizing process, one whereby an element of the system is replaced with a new element so as to store more information at less energetic cost. For example, the German biophysicist Bernd-Olaf Kuppers found an elegant way to reconcile the paradox of increasing information. Life is biological information, and the origin of life is the origin of biological information. Information has different aspects: syntactic (as in information theory), semantic (function and meaning of information for an organism's survival), and pragmatic (following the German physicist Carl-Friedrich Von Weizsacker, "information is only that which produces information"). Since evolution depends on the semantic aspect of information, there is no contradiction with the second law of Thermodynamics, which only deals with the structural aspect of matter (i.e., the syntactic aspect of information). The origin of syntactic information relates to the prebiotic synthesis of biological macromolecules. The origin of semantic information relates to the self-organization of macromolecules. The American biologist Christopher Langton has emphasized that living organisms use information, besides matter and energy, in order to grow and reproduce. In living systems the manipulation of information prevails over the manipulation of energy. Life depends on a balance of information: too little information is not enough to produce life, too much can actually be too difficult to deal with. Life is due to a reasonable amount of information that can move and be stored. Life happens at the edge of chaos. Ultimately, life is a property of the organization of matter. As the Canadian biologist Lionel Johnson put it, a bio-system can be compared to an information processor, whose job is to continuously extract, store and transmit information. Two fundamental and opposed forces compete, one leading towards increased uniformity (and lower information) over "ecological" time and one leading towards increased diversity (and greater information) over "evolutionary" time. This results in a hierarchy of living organisms, which has at the top the one species that developed the best strategy of energy extraction and storage, the highest resource utilization and the least dissipation (this is a reworking of a principle due to Alfred Lotka in the 1920s). Extracting information requires an energy flow, which in turns causes production of entropy. This can also be viewed from the point of view of communication: dissipative structures can exist only if there is communication among their components, whether in the form of genetic code (communication over stime) or societies (communication over space). The biosystem is, ultimately, an information processor and a communication network. At the same time, the Hungarian chemist Tibor Ganti views life as the combination of of two systems: metabolism and information control. The simplest form of life, in practice, is the "chemoton": an autocatalytic cycle coupled with an information molecule. Ganti's living organism, therefore, looks more like a computer than a program, because it includes the "hardware". Life without the hardware is not life, it is just the process that generates life. It also takes that "information molecule" to have life. Lives The British biologist John Maynard-Smith defined progress in evolution as an increase in information transmitted from one generation to another. The key to evolution is heredity: the way information is stored, transmitted and translated. Evolution of life as we know it relies on information transmission. And information transmission depends on replication of structures. Evolution was somewhat accelerated, and changed in character, by and because of dramatic changes in the nature of biological replicators, or in the way information is transmitted by biological replicators. New kinds of coding methods made possible new kinds of organisms. Today, replication is achieved via genes that utilize the genetic code. But this is only the latest step in a story that started with the earliest, rudimentary replicators, the first genes. The first major breakthrough in evolution, the first major change in the technique of replication, was the appearance of chromosomes: when one gene is replicated, all are. A second major change came with the transition from the solitary work of RNA to the dual cooperation of DNA and proteins: it meant the shift from a unitary source of replication to a division of labor. Metabolism was born out of that division of labor and was facilitated by the chemical phenomenon of autocatalysis. Autocatalysis allows for self-maintenance, growth and reproduction. Growth is autocatalysis. Early, monocellular organisms (prokaryotes) evolved into multicellular organisms (eukaryotes). The new mechanism that arose was gene regulation: the code didn't simply specify instructions to build the organism, but also how cells contributed to the organism. Asexual cloning was eventually made obsolete by sex, and sex again changed the rules of the game by shuffling the genetic information before transmitting it. Protists split into animals, plants, fungi, that have different information-transmission techniques. Individuals formed colonies, that developed other means of transmitting information, namely "culture"; and finally social behavior led to language, and language is a form of information transmission itself. Each of these steps "invented" a new way of coding, storing and transmitting information. Maynard-Smith also introduced Game Theory into Biology. The premise of game theory is that individuals are rational and self-interested Maynard Smith applied this definition to populations (instead of individuals) and interpreted the two attributes biologically: rationality means that population dynamics tend towards stability, and self-interest means fitness relative to the environment. The primacy of energy flows In the beginning was energy, matter came later. The American physicist Ronald Fox showed how, from the beginning, it was energy flows (lightning, volcanic heat) that allowed for the manufacture of unlikely molecules such as aminoacids that are the foundations of life. Life seems to be, ultimately, a process about storing and using energy. Biological events correspond to changes in flows of energy. Organisms use energy to excite monomers until they start creating polymers spontaneously. Eventually, the organism reaches a state in which polymers help produce (synthesize) polymers. Fox speculates that organisms used an abundant natural source of energy (phosphate-bond energy), that was created during an "iron catastrophe". That new flow of energy created a new kind of matter: living matter. Biological evolution was subsequently driven by energy regulation and storage. Fox used nonlinear thermodynamics, and therefore chaos theory, to show how complex structures could then spontaneously emerge. The nervous system makes sense in this scenario because it provides a biological advantage: it allows the organism to rapidly simulate the outcome of nonlinear events, that are, by their own nature, very hard to predict. Rapid simulation is the only way that the organism can predict what will happen, and is therefore essential to survival. Fox’s theory is all based on the simple idea that whatever happened was driven by new flows of energy, and that life is about storing and using energy. Even culture itself (i.e., human civilization) can be viewed as a new flow of energy that is creating a new form of life. A Hierarchy of Lives The reason why so many theories tend to identify the second law of Thermodynamics as the principal driving force of biological order is that it is the only physical law that distinguishes between past and future, the only one that can explain irreversible processes. And such are evolution and growth. The temptation is irresistible. But the true implications of the law of entropy (and even the very definition of entropy) are far from being well understood. The American physicist David Layzer found another way out of the paradox of creation of order: if entropy in the environment increases more than the entropy of the system, then the system becomes more ordered in that environment. Therefore, entropy and order can both increase at the same time without violating the second law of Thermodynamics. In other words: if the expansion of a set of systems is so quick that the number of states which are occupied increases less rapidly than the number of states which are available (i.e., the phase space gets bigger), entropy and order can increase at the same time. Unlike Prigogine, Layzer does not need to assume that an energy flow from the environment of a system can cause a local decrease in entropy within the system. Entropy and order increase together because the realization of structure lags behind the expansion of phase space. Furthermore, this property is not exclusive of biological systems, but shared by astronomical systems as well. Drawing from Shannon's theory of communication, Layzer then defines information as the difference between potential entropy (the largest possible value that the entropy can assume under the specified conditions) and actual entropy. As actual information increases, actual entropy decreases (information is "negative" entropy, as in Shannon's theory). Potential entropy is also potential information: maximum entropy equals maximum information. In biological and astronomical systems the potential entropy may increase with time, thereby creating information if it increases faster than actual entropy. In particular, both contraction and expansion of the universe from an initial state of thermodynamic equilibrium would generate potential entropy. Genetic variation always generates entropy as information flows unidirectionally from the genotype to the phenotype: when it makes the distribution of genotypes more uniform in a genotype space, it generates entropy and destroys information; when it allows the population to populate previously uninhabited regions of the genotype space, it generates potential entropy without necessarily generating entropy. Therefore, Layzer thinks that biological evolution is not driven by the growth of entropy (as a counterweight to the loss of order), and it is not (directly or indirectly) driven by the second law of Thermodynamics. That law presupposes certain initial and boundary conditions that are not present in biological systems. Influenced by the theory of the Russian biologist Ivan Schmalhausen that evolution is a process of hierarchical construction, Layzer thinks that there is a single universal law governing processes that dissipate order, but order is also generated by several hierarchically linked processes (including cosmic expansion and biological evolution). The Irreversibility of Life Not everybody agrees with Prigogine’s view of living systems as dissipative structures and with Schroedinger's view of life as "negentropic". A law known as "Dollo's law" states the irreversibility of biological evolution: evolution never repeats itself. Darwin's natural selection does not necessarily prescribe progress or regression, does not imply a direction of evolution in time, it only states an environmental constraint. Indirectly, Dollo's law does: it prescribes a trend towards more and more complex, and more and more ordered, living structures. Dollo's law expresses the visible fact that reproduction, ontogeny and phylogeny are biological organizations whose behavior is irreversible: both during growth and during evolution. Entropy of biological information constantly increases. We evolved from bacteria to humans, we grew from children to adults. The goal of the unified theory of evolution put forth in the 1980s by the biologist Daniel Brooks and the philosopher Edward Wiley is to integrate this law with natural selection. Unlike Prigogine, Wiley and Brooks believe that biological systems are inherently different from dissipative structures. Biological systems, unlike physical systems, owe their order and organization to their genetic information, which is peculiar in that it is encoded and hereditary. Dissipation in biological systems is not limited to energy but also involves information, because of the genetic code, which is transmitted to subsequent generations. Organisms simply live and die, they don’t evolve. What evolves is the historic sequence of organisms, which depends on genetic code. The genetic code must therefore be put at the center of any theory of evolution. Unlike most theories of information, that use information to denote the degree to which external forces create structure within a system, Brooks-Wiley's information resides within the system and is material, it has a physical interpretation. It resides in molecular structure as potential for specifying both homeostatic and ontogenetic processes (processes for, respectively, maintaining internal equilibrium and growing). As the organism absorbs energy from the environment, this potential is actualized and is "converted" into structure. What they set out to prove (following Lotka's original intuition and exploiting Layzer's ideas) is that evolution is a particular case of the second law of Thermodynamics, that Dollo's law is the biological manifestation of that second law. Biological order is simply a direct consequence of that law. The creation of new species is made necessary by the second law and is a "sudden" phenomenon similar to phase changes in Physics. Phylogenetic branching (the creation of new species) is an inevitable increase in informational entropy. In this scenario, the interaction between species and the environment is not as important in molding evolution: natural selection mainly acts as a pruning factor. Over short time intervals, biological systems do behave like dissipative structures. But over longer time intervals, they behave like expanding phase space systems (as proved by Layzer). Their relevant phase space is genetic, an ever increasing genetic phase space. The Brooks-Wiley theory is Darwinian in nature, as it subscribes to the basic tenet that evolution is due to variation and selection, but, in addition, it also allows the possibility for evolution to occur without any environmental pressure. The Origin of Form In the 1890s, the German physiologist August Weismann realized that living organisms exhibit a dichotomy: a piece of the organism's machine is designed to reproduce and another piece is designed to achieve form. One needs both in order to specify an organism. In a sense, Weismann was the Descartes of biology: he separated reproduction and "soma" (form), genetics and morphogenesis. So one can study genetics without studying development, and viceversa. One of the most puzzling features of life is, indeed, development. During development, cells split and split and split. Every time a cell splits, the new cells inherit (almost) exactly the same genes. But then, mysteriously, some cells become liver cells and some cells become bone cells and some cells become blood cells. Somehow a cell knows which proteins it has to make, and when and how many of it. If they run the same program, how come that two cells become two different things? And how do they know the position where those two things have to be? Not surprisingly, Weismann concluded, logically, that each cell must include a different set of genes. We have, instead, learned that each cell includes the same set of genes, but a cell's genes are "regulated" in such a manner than only some are active. Each cell has the same set of genes, but each cell has different genes active. Nonetheless, the question remains: what determines which genes are switched on and off in a given cell? How do "regulatory" genes know that a cell has to become part of a hair rather than a liver? Whatever the mechanism, it must be extremely reliable, because billions of humans get eyes in their face and not in their feet. Even more striking is the fact that zebras have black and white stripes: how do those cells know that they have to be white or black? And what causes the skin of the zebra to have stripes, rather than a uniform color? (The British mathematician Alan Turing proposed a solution based on the properties of standing waves) The British biologist D'Arcy Thompson argued that genetic information alone does not fully specify form. Form is due to the action of the environment (natural forces) and to mathematical laws. Form arises because of mathematical and physical properties of living matter, just like the shape of nonliving matter. Form is a mathematical problem, and growth is a physical problem. The form of an object is the resultant of forces. By simply observing the object, we can deduce the forces that have acted or are acting on it. This is easily proved of a gas or a liquid, whose shape is due to the forces that "contain it", buit it is also true of solid objects like rocks and car bodies, whose shapes are due to forces that were applied to them. The formative power of natural forces expresses itself in different ways depending on the "scale" of the organism. Mammals live in a world that is dominated by gravity. Bacteria live in a world where gravity is hardly visible but chemical and electrical properties are significant. Ultimately, D'Arcy believed that living organisms owe their form to a combination of internal forces of molecular cohesion, electrical or chemical interaction with adjacent matter, and global forces like gravity. Differentiation Genes, obviously, do not carry all the information needed for an organism to develop. How do cells of many different kinds come to occupy the "right" position in space? How do brain cells grow in the brain rather than, say, below the armpit? The phenomenon is even more mysterious because we now know that the early embryos of many animals, from insects to mammals, exhibit the same spatial pattern of activity of the same group of genes, before a morphological structure is created. A body is shaped by the orderly movement of billions of cells to the locations that specify their role. Cells are not genetically programmed to perform a specific role, but during development they become specialist. It appears that what a cell will do for the rest of its life depends on where its journey ends. "Growth" is this mass migration of cells towards an unknown destination that will determine their future. "Pattern formation" is the mechanism by which cells in different parts of a developing organism acquire different fates (and constitutes the main concern of Developmental Biology). Today, we believe that an organism is made from a very large number of autonomous cells which can interact among each other and that the whole functional organism "emerges" (i.e., arises) from local interaction of cells. Little is known about the physical process that allows this to happen, but cells in the embryo appear to be able to regulate their adhesion to surfaces and to other cells and they appear to do this to change shape or move. Self-formation While Chemistry is still moot about this phenomenon, information-based hypothesis abound, and the very first one was advanced by Alan Turing in person: a uniform distribution of chemicals can develop spontaneously in a wave of regularity. This would explain, incidentally, why Nature prefers repeated patterns. The American biologist Stuart Kauffman views the problem of cell differentiation as a problem of networks that search for stability. Each cell is equipped with the same network of genes, but the process that is occurring within each network is different: different genes are active in different cells. There is an almost infinite number of combinations in which genes can be active in a cell, but only a few of these combinations (precisely, the square root of the number of genes)correspond to mathematical "attractors". In the imaginary landscape of all possible genetic processes (the epigenetic landscape), there are basins of attraction. Those attractors correspond to the cell types that will arise. Topobiology The American biochemist Gerald Edelman explains location-dependent development of body cells (e.g., how a cell knows where in the body it is supposed to grow in order to generate the shape and function of the animal) by assuming that development is based on topo-biological events which are regulated by cell-adhesion and substrate-adhesion molecules on the surface of the cell. In other words, a cell's competence is due essentially to its location. In detail, the story reads like this. Living systems exhibit three properties that allow them to exist: heredity, variation in their hereditary material, and competition as the environment changes. Living systems are self-replicating systems, whose genome undergoes mutation and whose variant individuals undergo natural selection. Characteristic of living systems is development, in particular morphogenesis, the emergence of form during embryonic development. Roughly the same cell types appear in different parts of the body. The difference in position and shape results from the interaction of a number of driving forces (namely cell division, cell motion and cell death), which determine the number of cells in a particular region, and regulatory processes (namely cell adhesion and cell differentiation), which determine the interaction among cells. Pattern, and not mere cell differentiation, is the evolutionary basis of morphogenesis. The cell surface, not its core, plays the fundamental role in this process, because it mediates signals from other cells and links with other surfaces to form tissues. A sequence of interactions between certain special types of genes via epigenetic signal paths provides the basis of pattern by controlling temporal sequences of mitosis, movement, death and further signaling. Epigenetic landscape An apparent paradox is that different genetic programs can produce the same organism. In most cases, far less than 50% of the genes of an individual are shared with individuals of the same species. The individuals of a species differ in all sorts of ways, but somehow their genetic programs are tolerant to such differences and eventually yield individuals of the same species. In the 1950's the British genetist Conrad Waddington proposed a possible solution to the apparent paradox: the development of an individual is immune to the pull of the genes. Development is "canalized". He imagined an "epigenetic landscape" created by the concurrent pressures of the environment and the genetic program. Development occurs as a traversing of this landscape. The landscape varies from individual to individual, but it always maintains its fundamental shape of a gently sloping surface, that ends in the same valley. No matter how the landscape is traversed, the motion will always end in that valley. Catastrophes Rene' Thom, the French mathematician who "invented" catastrophe theory, assumed that the fundamental problem of biology is a topological problem: how form is built. The biochemistry of life should be explained by morphogenesis, not the other way around. Catastrophe theory is basically a classification of the ways in which forms can change into other forms. Morphogenesis is due to the disappearance of some attractors (in the epigenetic landscape) and the capture by new attractors, i.e. the new form. Death is easily defined: the trasformation of a metabolic field into a static field. On the contrary, the birth of life would require an "infinite" number of local transformations in order to achieve the "anabolic" transformation from static to metabolic (from simple ingredients to the complex structure of living tissue). Furthermore, once life occurs it is not clear why it stops at all: the underlying processes are reversible, therefore life should continue forever. Vitalism Genes do not carry all the information needed to specify the development of an organism. The same genetic program in two cells yields a blood cell and a liver cell. Somehow there must be other "information" available that tells one cell to become a blood cell and the other to become a liver cell. One clue to the solution of this mystery is that, as cells differentiate within the organism, different genes are "expressed" in different cells. At the end of the 19th century, the German embryologist Hans Driesch realized that a mutilated embryo would still develop into a fully-functioning living organism. He could not find any rational explanation and posited the existence of a "life force", or "entelechy". This was a variation on the old theory of "vitalism": that organic matter is fundamentally different from inorganic matter due to the presence of a vital principle. Driesch’s entelechy was a goal-directed (or "teleological") organizing process that would guide morphogenesis, regardless of any other information. Entelechies are organized in hierarchies (so that one doesn't need an entelechy for every single organism that can possibly exist). Then in the 1930s biologists such as Paul Weiss and Hans Speman (the first one to envision cloning by transferring the nucleus from one cell to another) hypothesized that "organizing fields" helped organisms take their shape. The British geneticist Conrad Waddington gave these fields a mathematical meaning with "chreodes", developmental pathways (channels) in his epigenetic landscape: form follows the channels rather than wander in other parts of the landscape. The German physicist Walter Elsasser concluded that Physics is not enough to explain life, and proposed the expansion of Physics to "biotonic" laws. In 1976 the American mathematician Ralph Abraham introduced a similar notion, that of "macrons": a macron is a collective vibrational pattern (many things that start vibrating together in synchrony). Abraham showed that macrons are ubiquitous in nature (in solids, liquids and gases). The Australian physicist Paul Davies also resorted to a sort of life force in order to explain the origin of life, but this "life force" is, in his opinion, a kind of software program. Davies thinks that science must accept "information" as a fundamental quantity of the universe, that can be traded by "informational" forces the same way that matter is traded by physical forces. The natural laws of informational forces must be compatible but not reducible to the laws of physical forces. The Memory of Nature and Morphic Fields The British philosopher and biochemist Rupert Sheldrake offered a neo-Aristotelian view of life and nature. Sheldrake views the growth of form as one of the fundamental processes of Nature. The foundation of Sheldrake's concept of "formative causation" is the idea that memory is inherent in Nature (an idea borrowed from the nineteenth century biologist Samuel Butler). Natural systems inherit a collective and cumulative memory from all previous systems of their kind, regardless of time and space separation; and natural systems in turn contribute to the growth of this collective and cumulative memory. Habits are inherent in the nature of all organisms because of the memory that organisms inherit from previuos organisms of the same kind. For living organisms, not only genes are inherited, but also habits, which include development habits such as morphogenesis (the growth of form). The universal memory expresses itself through "morphic fields". Morphic fields are an organizing principle of Nature. A morphic field is a field (or pattern or order or structure) of form. Such fields have a kind of built-in memory derived from previous forms of a similar kind. Each natural system has its own morphic field that shapes its behavior. There is a morphic field for pears, whales, crystals, etc. There is a nested hierarchy of fields within fields. Morphic fields evolve by natural selection. Morphic fields are responsible for form and organization (in biological as well as material systems). The morphic field of a system derives from morphogenetic fields associated with all previous similar systems (across both space and time). "Morphic resonance" is the process by which the past becomes present, i.e. it is the process of transmitting formative-causal information across space and time. "Morphic resonance" is the process by which the form of a system is influenced by the forms of past similar systems through the morphic field. The morphic field influences the form of a system, and, in turn, the form of the system influences the field and thus any future form of similar systems. The more similar an organism is to previous organisms, the stronger it "resonates" with (learns from) them. Individual memory is simply self-resonance: an organism resonates with its own past, i.e. it "remembers" it. Conversely, there is a universal memory that all forms share, the form of all forms (which he compares to Bohm’s "implicate order"). The persistence of the material form of a system depends on the continuous application of the morphic field on that system, which is, in turn, continuously recreated by morphic resonance. By "form" Sheldrake means more than just shape: spatial order, including the internal structure. He points out that form is not matter/energy: the total amount of matter/energy in the universe is the same before, during and after the existence of an organism, but the existence of the organism causes a change in the way matter/energy is organized. Form and energy are inversely proportional: energy expresses a principle of change, whereas form expresses resistance to change. Formative causation implies, for example, that a new pattern of behavior should be transmitted across space and time to individuals of the same species: as individuals of the species learn something somewhere, other individuals of the same species, no matter where they are located, should be learning it too (to some extent). Sheldrake believes that each species has its own fields, and within each organism there are fields within fields. Within each of us there is the field for the brain and the heart; within, are fields for different tissues inside these organs, and then fields for the cells, and fields for subcelluar structures, and so on. Such fields organize not only the fields of living organisms, but also the forms of crystals and of molecules. Each kind of molecule has its own kind of morphic field. So does each kind of crystal, each kind of organism, and each kind of instinct of pattern of behavior. These fields are the organizing fields of nature. There are many kinds of them, because there are many kinds of things and patterns in nature. The development of organisms is regulated by such morphic fields, and so is the organization of behavior. Genes carry only a minuscule part of the biological information in nature. Most of inheritance depends on the memory which is carried within the organizing fields of an organism. This memory is a kind of cumulative memory which is constructed through a pool of species experience, depending on morphic resonance. Genes do not carry all the information needed to shape an organism. Genes interact with the morphic fields of previous organisms of the same species. Biological inheritance is about both genes and fields. Fields allow for Lamarckian inheritance of acquired characteristics. Inheritance of acquired characteristics occurs not because of transmission of genes but because of the effects of morphic fields, which are modified by individuals "learning" something and then influence the development of future individuals of the same species. Memory is not stored in the brain but it resonates with the organism's own past. And a collective memory underlies our mental life (similar to Jung's collective unconscious). Myths, rituals, traditions are expressions of that collective memory: morphic fields organize social and cultural patterns and through morphic resonance, rituals bring the past into the present, connect past individuals with present individuals. Memories are never completely private. In principle, anybody could tune into our "private" memories and "read" our mind. Sheldrake views all of Nature as a living organism. Nature is essentially "habit-forming", and all aspects of Nature are regulated by the priciple of habit. The "laws of nature" are therefore better described as "habits of nature". The habits of animals and plants give them their habits of growth and their habits of behavior, or instincts. (Sheldrake’s theory, alas, flies against the evidence: children still need to re-learn how to walk and speak, despite thousands of generations and billions of humans did that in the past, a fact that sounds like overwhelming evidence that there is no morphic field for common behavior). Beyond Chemistry: Tensegrity In 1993 the American physician Donald Ingber popularized the concept of "tensegrity". Living systems, at all hierarchical levels, stabilize through the interplay of two forces, one which is tensional and one which is compressive. Ingber reasoned that, since cells continuously die, their chemistry alone cannot be responsible for the evolution for form. What is maintained is the architecture. Therefore, Ingber focused more on Architecture than on Biology. He re-discovered two types of structures that exhibit spontaneous and resilient stability: the geodesic dome invented by the American physicist Buckminster Fuller (in which the geometry of the components constrains the Physics of the components, thereby immobilizing the whole structure) and the "pre-stressed" sculptures built by the American artist Kenneth Snelson (in which rigid components tense flexible components and flexible components compress rigid components, thereby "pre-stressing" the whole structure). These "tensegrity" structures share the property of optimizing structural stability while minimizing building material. Ingber proved that living cells (and, in particular, their internal framework, the "cytoskeleton") behave like tensegrity structures, and that principles of tensegrity also govern (at least) tissue formation. Geodesic forms abound in nature, from the cytoskeleton to some carbon atoms. Ingber believes that tensegrity accounts for the continuity of movement: when an organ moves, millions of cells are affected, and each one has to adapt to the movement of the others. A tensegrity structure allows for a balanced transmission of tension to the elements of the structure and guarantees the "harmony" of the whole structure. In other words, the structure does not break or fall apart, but redistributes tension and therefore redesigns itself. Ingber believes that life began in layers of clay, a substance whose atoms are arranged geodesically and whose porosity allows for the catalysis of chemical reactions such as the ones that led to the building blocks of life. Life developed before any genetic mechanism was present. Then DNA created a way to accelerate evolution. It is not a coincidence that pre-stressed and geodesic forms predominate in the living world. The Function of Growth The construction of form is, of course, only an aspect of growth. The basic question is: why do beings grow? What is the goal of growth? Why aren’t we born as adults? Wouldn’t it be simpler if we were born like adults and had to worry only about reproducing? We have to protect and nurture our offspring, which results in a great waste of energies and in lower survival rates. A species that did not need to grow would be highly efficient. Why do living things grow instead of being built? There might be a few reasons. The first one has to do with complexity. It would require a huge amount of specification to assemble a body, cell by cell, whereas "growth" is a process whereby each component of the system helps specify the system as a whole. One needs very little to start, and there is virtually no limit to how far one can go. A second advantage is that a system that is built from scratch is not as resilient, as easy to repair, as a system that has developed through a number of stages. Because growth is an on-going never-ending process, most faults (such as wounds, cuts, fractures) get repaired naturally. The system is tolerant to most faults and will still operate. In an artifact, most faults disable the entire system (a mere flat tire is enough to stop a very expensive vehicle) and may even destroy it (a mere washer was enough to blow up a space shuttle). Finally, a growing being better integrates with the environment. Because growth depends on the surrounding matter as well as the genetic program (i.e., we eat plants and animals, we breathe air, etc.) the resulting body is better equipped to cope with the challenges posed by our environment. In a sense, there are no "unpredictable" events, all possible accidents have been implicitly predicted in the way our body grows. Then the complementary question: why does growth stop? What is so special about our adulthood that makes it the terminal point of growth, after which decay begins? Why does growth end and fade into decay? When does decay really begin and why at that point rather than at any other point? And when does it really end? We know when a body is created, because all of a sudden we can see it and touch it, but we don’t really know when a body is destroyed, because it fades away slowly. Needless to say, things would be even easier if organisms did not decay, if we just lived forever... Interactivity The view of the gene as a "ghost in the biological machine", as the set of instructions for building living beings, was criticized by the American philosopher Susan Oyama on the grounds that it perpetuates the misleading model of nature-nurture dualism (inherited versus acquired characters). The western tradition assumes that form preexists its appearance in bodies and minds (e.g., as a genome). Information is the modern source of form: ubiquitous in the environment as well as in the genome. The development of an organism is traditionally explained as a dual, parallel process: on one hand, translating information in the genome ("nature"); on the other hand, acquiring information from the environment ("nurture"). Both processes are dependent on information. Information therefore regulates development. This view has deep cultural roots, but Oyama objects that it is nothing more than myth. Oyama's viewpoint is that information (e.g., from the genome) is itself generated, it develops. Information itself undergoes a developmental process. Opposed to both nurture and nature, Oyama argues that the form of an organism cannot be transmitted in genes or contained in the environment, and cannot be partitioned by degrees of coding: it is constructed during the developmental processes. Information in the genes and information in the environment are not biologically relevant until they participate in the processes that actually build form. Form emerges through a history of interactions at many hierarchical levels, and genetic form is but one of the "interactants". Form is the result of interactive construction, not the outcome of a preexisting plan. The distinction between inherited and acquired characters should be replaced by the notion of development systems. An organism inherits its environment, as much as it inherits its genotype. It inherits some competence, but also the stimuli that make that competence significant. Life and the Universe Life appears less and less like a weird exception to the rules of Physics and more and more like a natural consequence of the way our universe works. The British physicist Freeman Dyson was instrumental in building the field at the borders of physical, biological and information sciences. Inspired by the British physicist Jamal Islam, who calculated how matter would evolve in universes which expand forever, Dyson computed mathematically what life is and how it will evolve. A closed universe is doomed to collapse and life with it. Since a system's entropy is a measure of the number of alternative states of the system, the complexity of a living organism should be proportional to the negative of its entropy. Dyson even computed the entropy of a human being (the rate at which humans dissipate energy times the human body's temperature times the duration of a unit of consciousness): 10 to the 23th. Life is a form of order, and low temperature favors order. Life and intelligence are immortal, because sources of memory will grow constantly as the universe cools down. Interestingly, "life" for Dyson is not necessarily the stuff made of proteins. "Life resides in organization, not in substance". As the American physicist Steven Frautschi, among others, noted, there is a striking parallelism between the evolution of the expanding universe and the evolution of life on Earth: because life on Earth has a steady free energy source (the sun), it does not need to come to equilibrium and may even evolve away from it (as it did when it created more and more complex beings, such as ourselves); because the universe has a steady free energy source (the uniform expansion itself), it does not need to come to equilibrium and may even evolve away from it (as it did when it created more and more complex clumps of matter, such as galaxies). Both biological evolution and universe evolution could turn out to be consequences of non-equilibrium processes. The Omega Point The "omega point theory" of the universe advanced by the American physicist Frank Tipler was meant as a rigorous mathematical proof of the existence of an omnipresent, omniscient and omnipotent god. Tipler even calculated the likelihood that every human being be eventually resurrected, and conjured up a physical model of life in heaven, hell and purgatory, all based on Information Theory, Quantum Mechanics and Relativity Theory. His basic point is that life is "information coding" preserved by natural selection: a being is alive if it encodes information and such information is preserved over time by natural selection. Given this definition of life, it is possible to compute how much energy is sufficient and necessary to extend this process till the very end of time in a closed universe. Furthermore, a simulated universe is, for all purposes, a universe, and its inhabitants are, for all purposes, as real as us, because there is no way that the simulated beings can realize they are simply being simulated. We may well be just that: simulations inside a computer. Virtual reality is no less real than actual reality, because there is no way to distinguish one from the other. In a sense, only virtual reality exists. Tipler calculates the maximum amount of information needed to simulate brains and entire humans, by basing his conjectures on the Bekenstein bounds (the upper limit on information density, according to Quantum Theory). The "omega point" is the final singularity of the history of a closed universe, the point of infinite information, which is neither space nor time nor matter, but is beyond all of these and experiences the whole of universal history all at once. Tipler believes that our universe is a Taub universe, a universe which, after the expansion phase is over, will start contracting at different rates in different directions, thus leading to an oblate spheroid shape. In such a contracting universe, temperature will be higher in the "contracted" direction and the difference of temperature between that direction and the others will generate energy. The fact that a closed universe must be in an infinite singularity actually means that infinite energy will be produced. In a Taub universe the differential collapse becomes a source of free energy, which life can use to survive forever. This source of energy will be to eternal life what the Sun is to life on Earth. The finite singularity of the universe and eternal life happen to coincide… The Meaning of Life A more scientific way of asking "what is the meaning of life" is: "what is responsible for my existence?" Which law in the universe has caused some molecules to assemble and become my body and then grow to the stage I am at now? The law of entropy has widely been considered the "smoking gun" of the situation. Unfortunately, nobody seems to really know what "entropy" means. Macroscopically, entropy is the ratio of heat to temperature, which is not a very intuitive definition. Microscopically, it is the number of micro-states that implement a macro-state (Boltzmann's definition), an even less intuitive concept. The law of entropy is even less well understood. Macroscopically, it states that the entropy of the universe can never decrease. This statement is not very easy to relate to our daily lives. Its more microscopic formulation as "heat can never be completely converted into work" is much more useful for practical purposes. In other fields, it can be better understood as "order cannot be created, unless at the expense of creating disorder somewhere else" (as the chemist John Holmsted put it, "the creation of local order requires generation of global disorder"). Prigogine showed that the law of entropy is useful to classify in which ways a system can evolve: a "closed" system (one that is fully isolated from the rest of the universe) can only evolve towards increased entropy, i.e. increased disorder (but, needless to say, no system in nature is really closed); an "open" system that expels energy (or matter) can evolve to ever-higher levels of order in a state of equilibrium (a star is an example of such an open system); an "open" system that both expels and absorbs energy can evolve to ever-higher levels of order while always being far from equilibrium. From this, one can perceive a similarity between the last category and living systems, and therefore be tempted to infer that living systems "are" in fact that category. One problem is that the complexity of living systems is not easily reduced to an abstract category. Another problem is that many physical systems belong to the same category that we would not like to consider living. A dishwasher absorbs energy/matter from an outlet and a pipe and expels energy in the form of hot water down a drain, but that doesn't automatically entitle it to the rank of living system. But then a dishwasher was manually built, whereas living system build themselves from virtually nothing. That "encoding" of information is really the clue to the meaning of life. That's why information has become more and more the focus of attention. What sets living systems apart from physical systems is not the flow of energy/matter: it is the fact that whatever they do is to some extent due to a "program". Living systems are machines programmed to perform the tasks of growth, reproduction and evolution. The downside of this argument is that any information-based simulation of life (including one performed into a computer) qualifies as life itself. But this still doesn't answer the question: "which natural law is responsible for my existence?" Any living system is built on top of physical systems, of matter, of "stuff". There is no reason why its natural laws should be any different than the natural laws that work on stuff. We feel that the answer to that question must lie in a general property of the universe. Possibly the reason Physics still doesn't know the answer is that Physics still doesn't know the general properties of the universe. Universal Darwinism In view of recent progress in several disciplines, in which the Darwinian paradigm keeps recurring at different levels of organization (species, immune system, brain), it seems reasonable to assume that Darwinism is a universal principle, not limited to Biology. The British psychologist Henry Plotkin actually believes that Darwinism is likely to become the basis of all science, the idea spreading beyond biological evolution. "Universal Darwinism" will be a theory based on Darwinism but general enough to encompass everything. A likely candidate structure for an empirical science is one based on the concepts of replicator (an entity that can make copies of itself) and interactor (an entity that can propagate replicators in space and conserve them in time while interacting with the environment). The presence of this combination is evidence that evolutionary algorithms are at work. They occur in life, in the brain, in the immune system, in memes. Further Reading Abraham, Ralph: ON MORPHODYNAMICS (Aerial Press, 1985) Davies, Paul: THE FIFTH MIRACLE (Simon & Schuster, 1999) Driesch, Hans: SCIENCE AND PHILOSOPHY OF THE ORGANISM (Black, 1908) Dyson, Freeman: INFINITE IN ALL DIRECTIONS (Harper & Row, 1988) Elsasser, Walter: THE CHIEF ABSTRACTIONS OF BIOLOGY (1975) Fox Ronald: ENERGY AND THE EVOLUTION OF LIFE (Freeman, 1988) Ganti ,Tibor: THE PRINCIPLE OF LIFE (Omikk, 1971) Hutchinson, Evelyn: THE ECOLOGICAL THEATER AND THE EVOLUTIONARY PLAY (1965) Islam, Jamal: THE ULTIMATE FATE OF THE UNIVERSE (Cambridge Univ. Press, 1983) Jansch, Erich: THE SELF-ORGANIZING UNIVERSE (Pergamon, 1980) Kauffman, Stuart: THE ORIGINS OF ORDER (Oxford University Press, 1993) Kay, James & Schneider, Eric: INTO THE COOL (Univ of Chicago Press, 2005) Kuppers, Bernd-Olaf: INFORMATION AND THE ORIGIN OF LIFE (MIT Press, 1990) Layzer, David: COSMOGENESIS (Oxford University Press, 1990) Lotka, Alfred: ELEMENTS OF MATHEMATICAL BIOLOGY (Dover, 1925) Margalef, Ramon: PERSPECTIVES IN ECOLOGICAL THEORY (Univ of Chicago Press, 1968) Maynard-Smith, John: EVOLUTIONARY GENETICS (Oxford University Press, 1989) Maynard-Smith, John: THEORY OF EVOLUTION (Cambridge University Press, 1993) Maynard-Smith, John & Szathmary Eors: THE ORIGINS OF LIFE (Oxford University Press, 1999) Maynard-Smith, John & Szathmary Eors: THE MAJOR TRANSITIONS IN EVOLUTION (W. H. Freeman, 1995) Morowitz, Harold: ENERGY FLOW IN BIOLOGY (Academic Press, 1968) Morowitz, Harold: FOUNDATIONS OF BIOENERGETICS (Academic Press, 1978) Morowitz, Harold: ENTROPY AND THE MAGIC FLUTE (Oxford University Press, 1993) Odum, Eugene: FUNDAMENTALS OF ECOLOGY (1953) Oyama, Susan: ONTOGENY OF INFORMATION (Cambridge University Press, 1985) Plotkin, Henry: DARWIN MACHINES AND THE NATURE OF KNOWLEDGE (Harvard University Press, 1994) Plotkin, Henry: EVOLUTION IN MIND (Allen Lane, 1997) Prigogine, Ilya: FROM BEING TO BECOMING (W.H.Freeman, 1980) Schroedinger Erwin: WHAT IS LIFE (Cambridge Univ Press, 1944) Sheldrake, Rupert: A NEW SCIENCE OF LIFE (J.P. Tarcher, 1981) Sheldrake, Rupert: THE PRESENCE OF THE PAST (Times Books, 1988) Speman, Hans: EMBRYONIC DEVELOPMENT AND INDUCTION (Yale Univ PRess, 1938) Thompson, D'Arcy: ON GROWTH AND FORM (Cambridge University Press, 1917) Tipler, Frank: THE PHYSICS OF IMMORTALITY (Doubleday, 1995) Ulanowicz Robert: GROWTH AND DEVELOPMENT (Springer-Verlag, 1986) Weber, Bruce, Depew David & Smith James: ENTROPY, INFORMATION AND EVOLUTION (MIT Press, 1988) Weismann, August: THE GERM-PLASM (Scribner's, 1893) Weiss Paul: PRINCIPLES OF DEVELOPMENT (Holt, 1939) Weizsacker, Carl-Friedrich von: DIE EINHEIT DER NATUR (1971) Woltereck, Richard: GRUNDZÜGE EINER ALLGEMEINEN BIOLOGIE (1932) Wicken, Jeffrey: EVOLUTION, INFORMATION AND THERMODYNAMICS (Oxford Univ Press, 1987)