Skip to Content

Intelligent design

On the origin of the architectural species

Galapagos finches by John Gould, from Darwin’s Voyage of the Beagle, 1845.

The oft-invoked analogy of the modern building to the human body (structural frame to skeleton, building enclosure to skin, mechanical systems to respiratory systems) is as apt as it is clichéd. Yet it falls short in that the body rather vaguely described—skeleton, skin, respiratory system—isn't specifically human, nor even specifically mammalian. The typical analogy stops short because it doesn't begin to account for the vast differences in the bodies and forms of various species of animal—or building.

In his revolutionary treatise of 1859, On the Origin of Species, Charles Darwin explained his powerful theory of the evolution of animal species. By Darwin's elegant algorithm, A) if individuals within a group are subject to variation, and B) if the environment results in a struggle for survival, and C) if individual characteristics are passed from one generation to the next, then D) over many generations, a species will evolve by a process of natural selection, that is, "survival of the fittest."

Buildings, too, evolve to meet environmental conditions, with certain architectural forms, details, and materials more suited to a given climate, site, or use. And, like the animal species Darwin studied, architectural forms must either adapt to their conditions—or perish.

In more than 150 years, not a single flaw has been found in Darwin's logic. His theory has proven powerful not only for understanding how the natural world all around us came to be but also for forming a cornerstone for entirely new lines of research and fields of study, such as modern genetics, that Darwin never imagined.

Given the importance of Darwin's theory to modern scientific thought and to cutting-edge scientific research, it is well worth considering the architectural parallels to his theory. Why do certain highly evolved building forms look the way they do, and what can we learn from this to further the state of cutting-edge architectural design today?

This parallel architectural theory of evolution, which I call Architectural Darwinism, is most evident in vernacular building forms, particularly those in harsh climates, where the practical considerations of creating shelter that worked with its environment were paramount. In vernacular architecture, these overriding concerns did not yield to stylistic predispositions or preconceptions, as they occasionally did in more formal architecture.

In Darwinian biology, the primary mechanism for the evolution is entirely involuntary (natural selection), whereas in Architectural Darwinism, the mechanisms are both voluntary and involuntary. The involuntary mechanism occurs where buildings with more advantageous variations and traits are more likely to survive over the centuries, and those buildings that were not as durably designed and constructed tend to fall prey to the effects of time and weather. The voluntary mechanism occurs where humans have carefully observed what has worked and what hasn't, and affirmatively designed the next building with the individual variations that have empirically proven to work well—a certain chimney location, a certain roof eave framing detail, a certain overall building form. In this way, the advantageous variation or trait is typically passed to the next generation of vernacular buildings.

Sometimes the technical logic behind the advantageous trait, and hence the evolution of a vernacular species, is fairly obvious. Second period (1725–75) "colonial" houses in New England were virtually the same as those in the South, except the northern version of the species had a very large central chimney to retain as much heat as possible within the house, and the southern version had the chimney on an outside wall, to cast off as much heat as possible to the exterior.

Just as obviously, antebellum plantation houses in hot, humid, flood-prone Louisiana were often raised on brick piers with an open ground floor, so that floods could wash through without damage. Further, a veranda wrapping all around the house shaded windows from the sun while allowing breezes through, tall windows and a square floor plan promoted cross breezes, and louvered attic dormers or a cupola passively vented and exhausted naturally rising hot air. All these advantageous characteristics evolved long before "resiliency" or "sustainability" or "passive design" became buzzwords. More often, the logic is not obvious, and highly evolved technical details are mistaken for mere stylistic or ornamental traditions. At first glance, the use of large diamond-shaped slate roof shingles in the vernacular architecture of the Alps (as opposed to smaller, rectangular slate shingles common in the United States and England) may seem a stylistic tradition rather than a technical evolution. However, on closer examination and analysis, the larger, diamond-shaped shingles are far more efficient in their use of material and in their resistance to wind-driven rain than their rectangular counterparts.

Diamond-shaped slate roof shingles in the Alps are more technically evolved than rectangular shingles because they use the material more efficiently and are more consistently watertight. Photo: ©

Similarly, the highly evolved technical logic of the traditional roof eave framing detail found in Rome is not readily apparent, and this beautiful detail could easily be mistaken for the purely ornamental. The detail transcends vastly different architectural periods and styles, from antiquity through the Medieval, Renaissance, and Baroque, to late 19th and early 20th-century Neo-Classicism, a strong clue that it is not merely stylistic. Its track record of durability is truly remarkable. Many examples, several hundred years old, constructed of relatively nondurable wood species such as pine, survive outdoors—unpainted, untreated, in a relatively rainy climate.

The triangular cut of Rome’s roof eave framing eliminates the beam end that is not needed structurally and the portion that would tend to rot. The roofing protects the beam from rain, and a series of functional cuts create regular drip edges to shed water. Illustration: Matthew Bronski PE.

The triangular form of the projecting beam end is exactly "what it wants to be" structurally. The triangular cut not only eliminates the portion of the beam end that is not needed structurally but also eliminates the portion that would tend to rot (via wicking of moisture through the exposed end) if the beam were simply cut at 90 degrees. The deep overhang of the roof over the beam protects it from moisture under all but the most severe wind-driven rain events. When rain does occasionally wet the beam, a series of beautiful but entirely functional cuts along the diagonal edge of the beam create drip edges to shed water at regular intervals. With such thoughtful, durable design, it is no wonder this detail has survived so well for centuries, despite the vulnerability of pine to rot in the humid, rainy climate of Rome.

Like the Roman eave detail, other highly evolved vernacular details and forms use local materials that are not, in and of themselves, durable within the local climate but have become durable through good design. The half-timbered buildings of England and central Europe are remarkable for the way the building form makes materials that degrade quickly with moisture perform durably even in a rainy climate. The materials they are built from, wattle (wood wicker) and daub (lime or clay plaster) degrade quite rapidly if left out in the rain, but the overall building form of an inverted stepped pyramid with cantilevered overhangs (known as jetties) at each floor serves to make the construction durable, even in the rain. The jettied overhangs shelter the walls from rain and shed water directly to the ground (not to the wall below), thus reducing the maximum possible accumulation of moisture at any point on the wattle and daub.

Darwin's revolutionary theory of evolution was based in part on his careful observation, documentation, and consideration of apparently ordinary things he saw around him on his voyages—for example, the slight differences in the shapes of the beaks of finches or in the thickness and shape of the shells of tortoises on the various islands of the Galapagos. The highly evolved vernacular forms of the English half-timbered, jettied building; the Alpine Swiss chalet; the antebellum Louisiana plantation house; and countless others are analogous to Darwin's finches and the Galapagos tortoises. Though none is immortal or invulnerable, each evolved to be particularly well suited to survival in its respective environment.

Darwin's masterful theory has been hailed as "the greatest idea anyone ever had" and continues to enable cutting-edge scientific research 150 years later. But his method—careful observation of the details all around us, and clear, simple analytical reasoning—is available to us all. In this age of global climate crisis, it has never been more important to analyze the details of highly evolved vernacular forms for the broad lessons they have to teach us about resilient, durable, sustainable design. If we can incorporate these lessons into our conception of the overall forms and details of building designs, we'll be far more responsive and responsible in meeting the formid­able environmental imperative confronting us today. ■