In November of 1863, Charles Darwin was too ill to put pen to paper, but not too ill to work on his metaphors. In a letter dictated through his wife Emma, Darwin tried out a new image, casting nature in the role of a discerning architect:
"Fragments of rock fallen from a lofty precipice assume an infinitude of shapes—these shapes being due to the nature of the rock, the law of gravity &c—by merely selecting the well-shaped stones & rejecting the ill-shaped an architect... could make many & various noble buildings."
In a recent short piece for Nautilus, I described two metaphors that Darwin used in developing his theory of evolution. A first was the well-known "natural selection" metaphor, in which nature is likened to a farmer who looks over his flock and breeds only those animals with desirable traits. As these selected traits take hold, new varieties emerge. A second was the less-known "wedges metaphor," in which nature is imagined as a vast field chock-full of rock wedges, each one representing a different species. As shocks are transmitted through the field, ill-fitting wedges pop out and well-fitting ones remain in place.
Darwin's architect metaphor, sketched in the 1863 letter, blends elements of these earlier two. Central to the natural selection metaphor is the idea of some agency that "selects" among varieties. Central to the wedges metaphor is a vivid—if inhuman—geological scene. The architect metaphor takes a geological scene and enlivens it with a human agent.
Why so many metaphors? Darwin is not just toggling between evocative images on a whim. Each comparison foregrounds a different aspect of the evolutionary process. The natural selection metaphor underscores the idea that certain traits will spread and stabilize as if some intelligence had selected them. The wedges metaphor foregrounds the tight economy of nature, the idea that there is limited space in which all of nature's luxuriance must fit. The architect metaphor highlights the idea that traits are generated in a chaotic process, new forms and features tumbling forth all the time.
The architect metaphor also does something else. Darwin notes this special something in his 1868 book, The Variation of Animals and Plants Under Domestication, in which he elaborates the architect metaphor:
"If our architect succeeded in rearing a noble edifice, using the rough wedge-shaped fragments for the arches, the longer stones for the lintels, and so forth, we should admire his skill even in a higher degree than if he had used stones shaped for the purpose."
A noble edifice emerging from a pile of scree—this would be quite impressive indeed. The field of wedges and the homely breeder are explanatory, but they do not exactly spark awe. Darwin's architect metaphor, on the other hand, urges us to view every species with wonder.
1. The letter was was written to Patrick Matthew, a Scottish farmer who, as Darwin conceded, had hinted at the mechanism of natural selection in a 1831 book on, of all things, ship-building.
2. Both the wedges metaphor and the architect metaphor involve rocks, but the rocks represent different things in each case. In the wedges metaphor, rocks represent different species, all vying for space; in the architect metaphor, rocks represent individual traits assembled together to form species.