Sequences, Sequences, and Sequences1
The World in One Dimension
The recent discovery of thousands of planets orbiting stars in our galaxy points to the likelihood of billions and billions of such planets across the universe. The odds are getting better that Earth is not the only planet that is physically and chemically capable of supporting something like life as we know it. But should we find “life” elsewhere in the universe, how would we know it? How would we conclude that some bag of chemicals is actually alive?
This book will argue that the answer is to be found in one-dimensional patterns, the linear arrangements that we call sequences. On Earth, sequences of DNA guide the functioning of the living world, sequences of speech and writing choreograph the intricacies of human culture, and sequences of code oversee the operation of our literate technological civilization. The persistence and diversity of life and civilization are made possible by one-dimensional patterns orchestrating three-dimensional activity. Physics and chemistry play crucial roles as well, but sequences are something special. They operate according to their own rules, and those rules have never been fully explored. It is time for them to get their due.
Back in the day, of course, our Earth was like all those other planets, capable of supporting life but not yet doing so. It was a stark place. Volcanoes erupted. Continents collided and mountains emerged. Water flowed and winds blew. Sediments deposited and oceans evaporated. As with every planet we know about, the behavior of the prebiotic Earth could be described and explained by the primeval processes of physics and chemistry following their universal and inexorable laws. Nothing to see here, move on.
What changed, then? When the first sequences arrived on Earth, probably in the form of RNA molecules, forces of nature like gravity and electromagnetism continued without interruption, and matter and energy were neither created nor destroyed. So, in one sense nothing changed. But sequences did guide matter and energy to become organized into things like cells and cities and computers, harnessing and channeling the forces of nature to maintain that organization and elaborate upon it. And in that sense, everything changed.
Which brings us to today. As literate humans, you and I occupy a complex habitat overseen by three kinds of sequences. One-dimensional molecular arrangements of RNA, DNA, and protein enable the diversity of the living world, sequences of sounds in speech and characters in text allow human culture to flourish, and patterns of zeros and ones in computer code make our high-tech civilization possible. Geophysical events like eruptions, hurricanes, earthquakes, tsunamis, landslides, and floods are still with us, but they are not what makes our planet interesting. Most of the time we attend to a world colonized and orchestrated by sequences.
What, then, are these sequences that have profoundly changed Earth’s environment? How did linear patterns of tiny molecules allow life to emerge from a background of ordinary physics and chemistry? How did sequences of vibrations in the air, marks on paper, and voltages in silicon allow civilization to emerge from a background of Tennyson’s “Nature, red in tooth and claw?”
These are the questions that animate this book. Fundamental to advancing our understanding is a simple but profound question asked by biophysicist Howard Pattee: “How does symbolic information actually get control of physical systems?”2 It is easy to envision a one-dimensional arrangement of molecules or letters or zeros and ones, but it is not so easy to envision how these patterns actually get control of the physical world, how they guide matter to behave one way rather than another.3
A fertilized egg packs into a one-dimensional pattern of DNA much of the three-dimensional information needed to make a chicken. How is it possible to get three dimensions of chicken out of a single dimension of genome? Further, the sequences of instructions that you need to assemble a bookcase are made of the physical substances of ink and paper, but no detailed study of the ink and paper will help you understand the meaning of the sequences. Something more is needed for the symbolic information (the instructions) to actually get control of a physical system (you).
On Earth or any other planet, we have learned that life does not require new laws of physics or chemistry, just some special, idiosyncratic infrastructure. In essence we start with physics and chemistry and we get biology for free. Further, human culture does not require new biological principles, just more special but different infrastructure. We start with biology and get civilization for free. In each case the special infrastructure that makes everything possible is built around the one-dimensional arrangements we call sequences.
The goal of this book is twofold. First, I would like to persuade you that sequences are indeed different and worthy of study in their own right. To create a unified account, I will show that sequences of DNA, language, and code have at least as much in common with one another as they do with the ordinary world of physics and chemistry. Second, I will offer a preliminary sketch of how they do what they do, their rules of operation. This will require an interdisciplinary march through physics, molecular biology, linguistics, anthropology, computer science, and other related disciplines. I have found this march exhilarating and I hope you will too.