The Universality of One-Dimensional Patterns
This book began at the beginning, on a planet Earth devoid of life and governed by the inexorable laws of physics and chemistry. It has proceeded as an inquiry into the general principles that might allow such a barren planet to organize its matter, first into the living world and later into the civilized world. The instruments of that inquiry have been the one-dimensional patterns we call sequences, patterns that were nowhere to be found on the prebiotic Earth but are impossible to escape in our literate technological civilization.
Back then sequences were nowhere; now they are everywhere. What can we surmise from this? My conclusion is that the sequences of DNA that organize life and the sequences of text and code that organize civilization are not different things but rather different examples of one kind of thing. Taking this path, using sequences as a lens to view the evolution of life and civilization, leads to some surprising results, especially for our understanding of human language.
Summarizing these sprawling results in a few sentences is not easy. Nonetheless, here are one dozen high-level themes that appear throughout the book:
- 1. Sequences are complex constraints. This is how they actually get control of physical systems, by harnessing and channeling the laws of nature, specifying this behavior rather than that. Constraints operate in the region between the certain and the impossible. They change probabilities. They can incline but not necessitate
- 2. Sequences are rate-independent; their timeless patterns are important, not their physical makeup. A process is rate-independent if speeding it up or slowing it down does not affect the result. A process is rate-dependent if changes in rate can change the outcome. The world of behavior and physics is rate-dependent, always moving
- 3. Sequences describe affordances, environmental patterns that offer opportunities for specific behaviors. These patterns and behaviors are independently described and arranged in the internal structure of sequences, in their grammars. The grammar of interaction allows unlimited composition of affordances, recombination of patterns to be perceived and behaviors to execute. The grammar of extension allows description of affordances distant in time and space, and subject to probabilities and contingencies. The grammar of abstraction allows sequences to be affordances for other sequences
- 4. Affordances can be perceived at all scales of the living and civilized worlds, from the enzyme-substrate relationship to human institutions like the criminal justice system. Biological and cultural evolution are processes of affordance discovery, exploitation, and memorialization
- 5. Sequences constrain the rate-dependent world through interactors, which recognize affordances and respond appropriately. Sequences govern interactors through either construction or configuration. Construction entails building interactors from elementary parts, as proteins are built from amino acids. Configuration entails changing the behavior of an interactor that already exists, as in parasitism and animal communication. If configuration is reversible, it is called allosterism
- 6. As systems of sequences become larger and more complex, their corresponding interactors become more discriminating in the range of environmental patterns they can recognize and the power and precision of their behavioral responses. Protein enzymes are powerful and specific catalysts, and technologies of measurement and manipulation allow humans to extend their perception and behavior into distant time and space
- 7. In biological and cultural evolution, sequential constraints often underdetermine the behavior of their interactors, leaving unconstrained degrees of freedom or don’t-care conditions. This minimizes the amount of sequence needed to execute a constraint, and admits variation that can lead to improvements in function
- 8. Sequences rely on external mechanisms for their interpretation and replication. These mechanisms are universal, able to process any sequence regardless of its functional relevance. Syntax is independent of semantics. Some of these mechanisms, like ribosomes, spliceosomes, and brains, are the complex and arbitrary result of millions of years of evolution. Other mechanisms, like protein folding, are lawful and dynamic
- 9. Interpretation and replication operate independently. Interpretation is functional and semantic; a sequence constrains an interactor through construction or configuration. Replication is quiescent and structural; a sequence is a passive template, and its meaning is of no consequence. Von Neumann’s self-reproducing automaton shows that a control mechanism is needed to switch a system of sequences between interpretation and replication
- 10. Sequence replication can be holistic or piecemeal. In cell division the entire genome sequence is replicated all at once; in horizontal gene transfer and human communication, short subsequences are replicated differentially. Holistic replication leads to tree-like descriptions of sequence lineages. Piecemeal replication leads to network-like descriptions. Taken together, they yield a reticulate pattern of inheritance
- 11. Sequences can be affordances for other sequences only if they are stable enough to be perceived. This gives an evolutionary advantage to permanent storage media like DNA and writing. Stability enables random access, self-reference at scale, and unlimited opportunities for reclassification of constraints. This allows systems of sequences to grow in complexity and cross the threshold of complication
- 12. Sequences needed for critical functions tend to be conserved across evolutionary time. Some of these form closed classes of short sequences, like prepositions, that are needed to support grammatical function. Others are large sets of interlocking sequences, like genetic regulatory networks and text-based human institutions, that are passed down as a set
DNA molecules, written texts, and computer code draw on very different alphabets, operate at different spatial and temporal scales, have different histories, and rely upon different mechanisms for interpretation and replication. However, the focus in this book has been on similarities rather than differences. What’s important are the observable regularities in the structure, behavior, and evolution of sequence-governed systems. As Carl Woese says, we should “think more about the process and less about the detailed forms it generates.”7 Ignoring the detailed forms and focusing on the process inevitably requires a change of perspective.
Despite Woese’s plea, most academic researchers spend most of their time studying the detailed forms. Molecular biologists and biochemists try to account for how genes guide the living world. Neuroscientists, linguists, and anthropologists try to account for how language guides human behavior. Computer scientists design code to guide the operation of computers and robots. This book has been more about the process; I prefer a unified theory to multiple unrelated accounts.