Evolution: Chance, Fate, or Design?
The universe has evolved from a nearly homogeneous state to the current diversity and structural organization seen throughout the cosmos. Weather systems evolve to form complex structures such as tornadoes and hurricanes. The fossil record documents the progression of life from simple microbes to multicellular organisms of increasing organizational complexity and diversity. These and numerous other observations document a pervasive tendency of systems that are open to energy sources to evolve complex and highly organized structures. There is little substantive debate regarding these facts. However, facts themselves do not address the deeper question of why systems evolve.
An argument commonly invoked against any natural law of evolution is that it violates thermodynamics. The Second Law of thermodynamics states that states of higher entropy are more stable than states of lower entropy. The 2nd Law thereby establishes an arrow of time in the direction of increasing entropy and stability. Since physics defines entropy as disorder, but evolution leads to greater order and organization, the argument is that evolution violates the 2nd Law and it is therefore incompatible with natural law.
Evolution does not, in fact, violate the 2nd Law. The 2nd Law applies to a system plus its surroundings. The evolution of life involves the coordination and organization of geological and biological processes within the biosphere, and this does involve a reduction in its entropy. However, the decline in the biosphere’s entropy is more than offset by the vastly larger production of entropy by the sun and surrounding space. The entropy of the overall system of the biosphere plus sun and space increases, in accordance with the 2nd Law. While the 2nd Law does permit evolution within the biosphere, it offers no explanation for why local entropy reduction and evolution occur. Evolution may obey the letter of the 2nd Law, but it certainly appears to violate the spirit of the 2nd Law.
Darwin’s explanation for the evolution of life was natural selection of the fittest. He defined the fitness of an organism by its reproductive success. Natural selection thereby ensures that the fittest individuals survive and pass their characteristics to succeeding generations. He postulated that reproduction sometimes introduces random changes in inherited characteristics. Selection of the fittest preserves beneficial changes in fitness and winnows out deleterious changes. Natural selection, together with random changes, allow species to adapt to changing conditions and to diversify to fill new niches.
Modern evolutionary synthesis integrates Darwin’s theory of natural selection with genetics. Genes control the physical characteristics of individuals and are passed on to succeeding generations. Mutations introduce random changes in the genetic code. Natural selection of the fittest leads to the spread of genes conferring adaptive benefits throughout a species’ gene pool and to the winnowing out of maladaptive genes. This leads to improvement in species’ adaptation to their ecological niches. The most successful species are those that are best adapted to their niches. A niche is not a fixed goalpost, however. A species’ niche constantly shifts as other species evolve. Species and niches within an ecosystem co-evolve together.
From a high-level perspective, the modern evolutionary synthesis appears to be well-documented. Biology describes species’ physical and behavioral adaptations to their environment. Adaptive responses to environmental changes have been measured in the laboratory and in the field. Genetic mutations are well established. Comparisons of species’ genomes reveal their shared ancestry across the evolutionary tree. Despite these well-documented facts, however, the evolution of life by natural selection of the fittest is not nearly as open-and shut as many scientists suggest.
First, the subject of fitness is not clearly established. Darwin applied fitness to individual organisms. Darwinian evolution leads to selection of the most competitive individuals, who can out-compete other individuals. This appears to apply in many cases, but it does not apply to eusocial species, such as bees. Bees cooperate with a complex division of labor. A beehive behaves more like a superorganism than a collection of individuals. Advocates of group selection, such as biologist E. O. Wilson, propose that natural selection can act on groups, not just individuals. Group selection promotes cooperative behavior among the individuals for the benefit of the group as a whole. Humans, too, have characteristics of a eusocial species, for which survival depends on cooperation and division of labor among individuals within families, tribes, or civilized societies. In humans, simultaneous selection pressures on individuals and on social groups might explain our conflicting tendencies of competition versus cooperation, of self-interest versus altruism, of cheating versus rule-abiding. In the other direction, Richard Dawkins argued in his book, The Selfish Gene, that natural selection is more appropriately applied to individual genes. Does fitness apply to genes? To individual organisms? To social groups? To multiple levels simultaneously?
Second, and more serious, the definition of fitness only applies to self-replicating systems that can pass their characteristics on to succeeding generations. Evolution is not limited to living systems, however. Simple pre-biotic chemical systems must have evolved to form the first self-replicating microbes (or macromolecules) before natural selection of the fittest could take over. A general principle of evolution needs to apply to all evolving systems, physical, chemical, and biological.
Third, fitness is not a valid property for physical or biological systems. By defining fitness as reproductive success and the ability to pass genes onto the next generation, “survival of the fittest” is reduced to the truism “the most successful succeed.” Like any truism, it may provide a useful conceptual framework, but the definition of fitness is circular and “survival of the fittest” is devoid of any physical meaning.
The 2nd Law of thermodynamics permits local evolution and reduction in entropy, but it offers no explanation. In response, researchers have long sought a new law of thermodynamics to complement the 2nd Law. Various versions of a 4th Law of thermodynamics have been proposed to explain the apparent drive of open systems to reduce local entropy and self-organize. However, none has been generally accepted.
The Santa Fe Institute, an organization dedicated to the evolution of complexity, concluded that complexity arises in many disparate types of systems, and that there likely can be no unified theory for evolving complexity. Twenty years later in a 2014 retrospective, David Pines, one of SFI’s cofounders, acknowledged that the dream of a unifying theory of complexity remained elusive.
Physics is deemed the ultimate arbiter of science, so we ask: How does physics interpret the origin and evolution of life? Physics accepts entropy, the arrow of time, randomness and evolution all as valid emergent descriptions. Emergent descriptions are empirical facts, based on observations of systems that are too complex to describe in complete detail. Emergent reality is a high-level statistical approximation of an underlying physical reality, which is described by the fundamental laws and particle fields of physics.
At the emergent level of biological and geological reality, the fossil record clearly shows the evolution and diversification of life over geologic time. Observations also show two of the three essential elements of natural selection: the transmission of genetic information to offspring and the introduction of new genetic information by random mutations. Missing, however, is a well-defined physical property on which a principle of selection can act to explain the evolution of either living or non-living systems.
A principle of evolution would have to select states of increasingly higher overall entropy, while also having localized regions of increasingly lower entropy and higher order. Preferential selection based on such a property would lead to local evolution of structural order, and it would be consistent with the 2nd Law. However, no such property of state is known to exist.
Natural selection of the fittest provides a general framework for evolution of self-replicating forms, but there is no emergent property on which a principle of selection can act that values more evolved states. Without a property of selection for evolution, physics can only fall back to randomness and sufficient time to explain the origin of life from simple chemicals. But how much time? Geological evidence suggests that simple cells formed as early as 100 million years after the formation of oceans. At the emergent level of description, the creation of simple cells, or even self-replicating macromolecules, by random interactions over a relatively short time span is problematic and remains unresolved. How does physics describe evolution at a fundamental level?
Physics describes a fundamental physical reality that is very different from the emergent realities of biology and geology. Physics describes objective physical reality, unperturbed by observation or other external interactions, as deterministic. Given that the universe, by definition, has no surroundings, the universe’s evolution is fundamentally deterministic. The future, as well as the past is set in stone and everything that happens is fate. This implies that the entire history of the universe and its current state of exceptional organizational complexity were encoded in an exceptional initial state of the universe. Physics, however offers no testable explanation for such an exceptional initial state. Its origin is problematic and remains unresolved. Even worse, physics cannot accommodate a fundamental arrow of time. Without an arrow of time, the concept of evolution is altogether meaningless.
Both emergent and fundamental levels of physical description have clear gaps in their explanation of evolution. There is no emergent-level property on which a principle of evolution can act. This leaves evolution as a matter of random chance, but it is problematic how unguided random chance can lead to the origin and evolution of life. At the fundamental level of physical reality, evolution is simply a matter of fate, encoded in the universe’s initial state. The origin of such an exceptional initial state, however, is unresolved. Both explanations leave significant unexplained gaps.
Gaps in the scientific explanations of evolution have led some to argue that evolution must be guided by a non- scientific explanation such as intelligent design. I agree that we need to consider explanations beyond the current physical interpretations, but I strongly disagree with the need to abandon science. To the question raised in this essay’s title, I respond “none of the above.”
Before physics subsumed thermodynamics as a statistical description and approximation of physical reality, thermodynamics was developed to understand heat engines and heat pumps. Thermodynamics defined energy to include ambient heat, in addition to the kinetic and potential energy of physics. Thermodynamics introduced the law of energy conservation as its first law. It defined the 2nd Law, not in terms of increasing disorder, but in terms of the dissipation of useful energy, as measured by its potential to do work, to ambient heat, with zero potential for work. It later defined entropy as an objective measure of dissipation. The irreversible dissipation of useful energy to ambient heat and concomitant increase in entropy defined the arrow of time as fundamental and objectively real within the framework of thermodynamics.
Lord Kelvin recognized the constructive power of dissipation in an article he wrote in 1862. He began by describing heat death, when all directed activity ceases, as the inevitable end-result when useful energy is entirely dissipated to ambient heat. He then proceeded to express a much deeper and overlooked idea. Backing off on the inevitability of heat death, he continued that the universe is in a state of “endless progress…involving the transformation of potential energy into palpable motion and thence into heat.” In essence, he asserted that a source of useful energy tends to defer dissipation by first utilizing it for palpable work, and “thence” dissipating it into heat. If an energy source defers dissipation by doing work on some other dissipative system, then that system could likewise defer dissipation and do work on other systems. The recursive deferral of dissipation for work to sustain other dissipative systems leads to an expanding network of systems of increasing interconnectedness and organization. This idea precisely expresses the evolution of organizational complexity for a dissipative process. Dissipative systems and processes can include mechanical, chemical, nuclear, or biological systems
When Lord Kelvin stated this idea, classical mechanics was well entrenched in physical thought. Kelvin’s idea (and thermodynamics, generally) was incompatible with classical mechanics, and it never gained a foothold and was largely ignored. While physical formalism has changed radically with the discovery of relativity and quantum mechanics, modern physics’ interpretation of physical reality has not fundamentally changed. Physics still interprets reality in terms of states, defined by the (now statistical) measurable positions and kinetic and potential energies of a system’s particles. Heat, entropy, and the arrow of time only exist as emergent properties and as statistical approximations describing a system’s actual underlying state.
The spectacular successes of modern physics and its formalism need not and are not questioned. However, the existing interpretations of modern physics reject fundamental dissipation and arrows of time. With no arrow of time, there can be no fundamental principle of evolution. It is time to reverse the historical mistake made when physics reinterpreted thermodynamics as a statistical approximation of physical reality.
In Reinventing Time, I reinterpret modern physics within the conceptual framework of thermodynamics. This preserves the formalisms of modern physics intact, while moving the interpretation of physics beyond the determinism of states to accommodate process and evolution as fundamental attributes of physical reality. In The Arrow of Functional Complexity, I propose a general physical principle of evolution.
