Complexity: An Energetics Agenda Energy as the Motor of Evolution 1. INTRODUCTION rom galaxies to snowflakes, from stars and planets to life itself, modern science is weaving an intricate pattern describing all of natural history—a sweepingly F inclusive view of the order and structure of every known class of object in our richly endowed Universe. Cosmic evolution—the heart of this broad scenario—is the study of the sum total of the many varied developmental and generational changes in the assembly and composition of radiation, matter, and life throughout all space and across all time. These are the physical, biological, and cultural changes that have produced, in turn and among other systems, our Galaxy, our Sun, our Earth, and ourselves. The result is a grand evolutionary synthesis bridging a wide variety of scientific specialties—physics, astronomy, geology, chemistry, biology, and anthro- pology, among others—a genuine narrative of epic proportions extending from the beginning of time to the present, from big bang to humankind. ERIC J. CHAISSON Our appreciation for evolution now extends well beyond the subject of biology; the concept of evolution, generally considered, has become a powerful unifying factor in all of science. Yet questions remain: How valid are the interdisciplinary continuities among Nature’s many historical epochs, and how realistic is our quest Eric J. Chaisson is at the Wright Center, for unification among them? Can we reconcile the observed constructiveness of Tufts University, 4 Colby Street, cosmic evolution with the inherent destructiveness of thermodynamics? Is there a Medford, Massachusetts; e-mail: single driver of fundamental change writ large? We especially want to know more [email protected]; Website: about the origins of the richly ordered and diverse structures spanning both the www.tufts.edu/as/wright_center. terrestrial and extraterrestrial Universe, notably those systems often characterized by the intuitive term “complexity”—a state of intricacy, complication, variety, or in- volvement, as in the interconnected parts of a system. Particularly intriguing is the rise of complexity over the course of time, indeed dramatically so within the past half-billion years since the end of the pre-Cambrian on Earth. Resembling a kind of neo-Platonism, perhaps some underlying principle, a unifying law, or an ongoing process does create, order, and maintain all structures in the Universe, enabling us to study everything on uniform, common ground—“on the same page,” so to speak. Recent research, guided by notions of beauty and symmetry and bolstered by vast new databases, suggests affirmative answers to some of these queries: Islands of ordered complexity—namely, open systems such as galaxies, stars, planets, and life forms—are more than balanced by great seas of increasing disorder elsewhere in the environments beyond those systems. All can be shown to be in quantitative agree- ment with the principles of thermodynamics, especially nonequilibrium thermody- namics. Furthermore, flows of energy engendered largely by the expanding cosmos 14 COMPLEXITY © 2004 Wiley Periodicals, Inc., Vol. 9, No. 3 do seem to be as universal a process in FIGURE 1 the origin of structured systems as any- thing yet found in Nature. The optimi- zation of such energy flows might well act as the motor of evolution broadly conceived, thereby orchestrating much of physical, biological, and cultural evo- lution [1]. 2. ARROW OF TIME Figure 1(a) shows an archetypal illustra- tion of cosmic evolution, the “arrow of time.” Regardless of its shape or orien- (a) This symbolic “arrow of time” highlights salient features of cosmic history, from its fiery origins tation, such an arrow represents an in- some 14 billion years ago (at left) to the here and now of the present (at right). Labeled diagonally tellectual guide to the sequence of across the top are the major evolutionary phases that have produced, in turn, increasing amounts of events that have changed systems from order and complexity among all material systems: particulate, galactic, stellar, planetary, chemical, biological, and cultural evolution. Cosmic evolution encompasses all of these phases. Time is assumed simplicity to complexity, from inorganic to flow linearly and irreversibly, unfolding at a steady pace, much as other central tenets are assumed, to organic, from chaos in the early Uni- such as the fixed character of physical law or the mathematical notion that 2 ϩ 2 ϭ 4 everywhere. verse to order more recently. That se- (b) Sketched here qualitatively is the rise of order, form, and structure typifying the evolution of quence, as determined by a large body localized material systems throughout the history of the Universe. This family of curves connotes the of post-Renaissance data, accords well widespread, innate feeling that complexity of ordered structures has generally increased over the course of time. Whether this rise of complexity has been linear, exponential, or hyperbolic (as drawn with the idea that a thread of change here), current research aims to specify this curve, to characterize it quantitatively. links the evolution of primal energy into elementary particles, the transforma- tion of those particles into atoms, in ditions more conducive to stellar and turn of those atoms into galaxies and Our appreciation for evolution planetary formation; now, at least on stars, and of stars into heavy elements, now extends well beyond the Earth, cultural evolution dominates. the evolution of those elements into the subject of biology; the concept of Change in surrounding environments molecular building blocks of life, of evolution, generally considered, usually precedes change in organized those molecules into life itself, and of has become a powerful unifying systems, and the resulting system intelligent life into the cultured and factor in all of science. changes have generally been toward technological society that we now greater amounts of order and complex- share. Despite the compartmentaliza- ity. tion of today’s academic science, evolu- Time’s arrow implies no anthropo- Figure 1(b) sketches the widespread tion knows no disciplinary boundaries. centrism; it is not pointing at us. The impression that material assemblages As such, the most familiar kind of arrow merely provides a mental road- have become more organized and com- evolution—biological evolution, or map symbolically mapping the rise of plex, especially in relatively recent neo-Darwinism—is just one, albeit im- increasingly complex structures, from times. This family of curves refers to portant, subset of a much broader evo- spiral galaxies to rocky planets to repro- islands of complexity comprising sys- lutionary scheme encompassing more ductive beings. Nor does the arrow tems per se—whether giant stars, buzz- than mere life on Earth. In short, what mean to imply that “lower,” primitive ing bees, or urban centers—not their Darwinian change does for plants and life forms biologically changed directly vastly, indeed increasingly, disorga- animals, cosmic evolution aspires to do into “higher,” advanced organisms, any nized surroundings. A central task of for all things. And if Darwinism created more than galaxies physically change complexity science aims to—or ought an intellectual revolution by helping to into stars or stars into planets. Rather, to—explain this temporal rise of orga- free us from the notion that humans with time, the environmental condi- nization. That is the objective of this basically differ from other life forms on tions suitable for spawning primitive paper. our planet, then cosmic evolution ex- life eventually changed into those favor- tends that revolution by treating matter ing the emergence of more complex 3. NONEQUILIBRIUM on Earth and in our bodies no differ- species; likewise, in the earlier Uni- THERMODYNAMICS ently from that in the stars and galaxies verse, environments ripe for galactic Cosmic evolution, as understood today, beyond. formation eventually gave way to con- is governed largely by the laws of phys- © 2004 Wiley Periodicals, Inc. COMPLEXITY 15 ics, particularly those of thermodynam- provided we reason in broad, interdis- FIGURE 2 ics. Note the adjective “largely,” for this ciplinary terms. is not an exercise in traditional reduc- Figure 2 schematically diagrams, tionism; no attempt is made here to along the lines developed by Prigogine “reduce” biology to physics, rather to [4], the emergence of structure in the broaden physics to include biology. For presence of energy flow. Physicists are of all the known principles of Nature, familiar with the type of curves at the thermodynamics has perhaps the most top; biologists more comfortable with to say about the concept of change—yet those at bottom. Upon crossing certain change dictated by a combination of energy thresholds that depend on a sys- chance and necessity, of randomness tem’s status, bifurcations can occur, and determinism. Even so, the cosmic- fostering the emergence of whole new evolutionary narrative is much too rich hierarchies of novel structures that dis- and diverse to be explained merely by play surprising amounts of coherent be- equilibrium thermodynamics. All struc- havior. Such dissipative structures ex- tures, whether galaxies, stars, planets, port some of their entropy (or expel or life forms, are demonstrably open, some of their energy) into the external nonequilibrated systems, with flows of environment with which they interact. energy in and out a central feature. And Accordingly, order