Life’s Creative Recipe

“Cells to Civilizations: The Principles of Change That Shape Life” A book by Enrico Coen

Is there a “grand unified theory” in biology? Developmental biologist Enrico Coen argues in “Cells to Civilizations: The Principles of Change That Shape Life” that just seven principles underlie the process of embryogenesis (how the embryo is formed), evolution, cognition and human culture. Coen’s book is ambitious and stimulating. Only time will tell whether his ideas will influence the way biologists think. In the meantime, “Cells to Civilizations” is good material for conversation and a worthwhile read.

Coen could be called a Renaissance man. He is a botanist, a developmental biologist and a geneticist. As an undergraduate, Coen waffled between chemistry and genetics, finally deciding upon genetics because the classes met later in the morning and provided coffee. Most famously, he showed that flowers are organized by three classes of genes into four circular patterns. His work has more recently focused on the evolution of leaf shape. He uses such diverse tools as genetics, molecular biology, 3-D imaging, multidimensional analysis and computer modeling of growth. It makes sense that a multidisciplinary biologist would seek to unite fields that were previously isolated from one another.

In “Cells to Civilizations,” Coen contends that seven principles, or “ingredients” — population variation, persistence, reinforcement, competition, cooperation, combinatorial richness and recurrence — “and the way they work together define ‘life’s creative recipe.’ “

“It is this recipe that lies at the root of how life transforms itself. The evolution of diverse organisms, the development of an egg into an adult, an animal learning of new relationships in its environment, and the attainments of human culture are all different manifestations of life’s creative recipe. They all depend on the way a common set of basic ingredients work together.”

The principle of combinatorial richness, for instance, appears in the genetic makeup of evolving populations, among the cocktails of regulatory proteins that pattern an embryo, in the wiring patterns of nerve cells within the brain, in the combinations of letters upon a page, and in the unique encounters between individuals in 15th century Florence, Italy, that contributed to the Renaissance.

Coen maintains that this worldview is essential in grasping the underlying mechanisms of biology, just as one must recognize that the principle governing the transformation of ice to water is the same one governing the transformation of water to vapor. “They are different manifestations of the same underlying process. This unifying perspective gives us a deeper understanding of what is happening than what we perceive by simply viewing each transition in isolation.” Through this principle we learn that the amount of energy experienced by water molecules determines their freedom of motion. Similarly, appreciating that the transformations that occur during embryonic development, evolution, in learning and in human culture arise through “common elements behind different living transformations can help us to understand the essence of each process, while also giving us a broader overview of events.” On the other hand, Coen warns against pushing comparisons too far. The principles are the same but the particulars are very different. The game of chess is an abstraction for war, he explains, but the squares in chess should not be used to plan a battle. Coen also discusses the controversial concept of memes — an attempt “to link culture and related biological processes more precisely.”

“For example, a unit of transmission called the meme has been proposed as playing a similar role in culture as a gene plays in evolution. A meme is an idea or activity that replicates and is transmitted from one human to the next, just as a gene may be passed from parent to child. While the notion of memes may be useful in emphasizing certain parallels between evolution and cultural change, it also invites confusion. What, for example, is the precise equivalent of natural selection that leads one meme to increase at the expense of another? The answer is far from clear, leading the geneticist Jerry Coyne to conclude that the problem with mimetics is that it ‘seems completely tautological, unable to explain why a meme spreads except by asserting, post facto, that it had qualities enabling it to spread.’ “

One feature that arises repeatedly in Coen’s account of biological transformations is the double feedback loop. In a double feedback loop, both positive and negative inputs regulate the level of a product, such as reproductive success, connections between two nerve cells or human achievement. In the case of reproductive success during natural selection, the success of some genes will promote expansion in future generations. This is the principle of reinforcement at work, and in this case it drives positive feedback. The unchecked success of these genes, however, will soon encounter environmental limitations. The principle of competition, at this point, creates negative feedback. Cooperation promotes further success in human achievement, while competition checks it. At times Coen’s arguments for the seven underlying principles of life’s creative recipe may seem to be semantic, but the synthesis of these ideas builds progressively throughout the book and comes together near the end. The reader should labor through the detailed lesson on the physiology of learning to reach a beautiful treatment of the mechanistic basis of creativity. Here, Coen breaks down the process to reveal a double feedback loop in which variation and persistence are tempered by reinforcement and competition. Creativity, he asserts, is another transformation within the biological world.

“Imagine Cézanne working on a canvas. After placing some initial patches of color, he may feel that some meet with his expectations, while others are not quite right or create surprising effects. He may then react to this mixture of expectations and discrepancies by adding more brush strokes, building the picture up, leading to further judgments and comparisons. The painting proceeds in this way as a critical dialogue between Cézanne and what he sees in front of him. He may be conscious of some of this dialogue, but much of it may also be happening nonconsciously — he may instinctively feel compelled to add some color here or there, or feel that a brush stroke works well or is not quite right.

“This creative dialogue involves a complex interplay between all the processes we have encountered — predictions, actions, and interpretations. Cézanne did not simply mix and place colors at random; based on his experience as a painter he predicted what sort of effect they were likely to have and used this knowledge to guide his actions. He then interpreted the colors he placed on the canvas, exploring their relationships and comparing them to the subject he was painting. The matches and discrepancies he found then led to further predictions and actions, and so the process continued. The painting emerged through a neural dialogue that wove together predictions, actions, and interpretations at multiple levels. By painting a picture, Cézanne may also have increased his skills, modifying his neural models so that he approached a painting in a slightly different way next time round. The result is not only a painting, but the propulsion of Cézanne’s brain through neural space.”

In contrast to the baseball metaphors of Stephen Jay Gould, or the classic rock lyrics of Sean Carroll, Coen’s metaphors and examples are taken almost entirely from the world of visual art. His previous book, “The Art of Genes,” likened embryonic development to the process of painting. In “Cells to Civilizations” the metaphors include the prehistoric cave paintings at Lascaux to the cubist paintings of Picasso. To illustrate the process of reinforcement in learning to recognize the proportions used by painters, he invokes a “Modigliani neuron.” To show that the world we perceive is limited by the mechanisms that have evolved to perceive it, Coen concludes the book with a lithograph by M.C. Escher, “showing a man looking at a picture of which he is part. Like Escher’s man we can never step out of our picture, but this does not mean that we cannot contemplate and try to understand the fascinating world of which we are an inseparable part.”

Deniz Erezyilmaz is a research assistant professor at Stony Brook University in New York. She is the author of several papers on evolutionary developmental biology, which have appeared in the journals Nature and Proceedings of the National Academy of Sciences.