I suspect that many people who pick up the Origin today hoping for inspiration and big ideas are frustrated to find themselves wading through a lot of details about horses, peas, and pigeons. For Darwin, the accumulation of facts was something of an obsession, and necessary to support his theory of natural selection. He recognized that the abundant data about variation in domestic animals and plants could illuminate processes of change in the natural world—even though quotidian facts about the habits, appearance, and breeding cycles of these species were seen as concerns of the farmer and not the naturalist.

What struck me most about the first chapter is how a provocative rumination about variation and inheritance of traits in domestic animals soon gives way to a long discourse on pigeons. When I first read it I had little knowledge of pigeons, and I had never heard of the fancy pigeons Darwin was talking about. This long discourse on an obscure bird so soon into the book was a mystery and, frankly, a bit of a letdown.

Yet it also led me to wonder why Darwin chose to single out these birds. “Believing that it is always best to study some special group, I have, after deliberation, taken up domestic pigeons,” Darwin tells us. It was a choice that made far more sense to readers in Victorian England. At the time, the pigeon fancy was a well-known and popular hobby. So when Darwin then launched into comparisons of the beaks of the English carrier and the short-faced tumbler, his readers may not have been as baffled as many today undoubtedly are.

First—what are these birds, and what made Darwin choose them over so many other domesticated species? At the time, fancy breeds of pigeons had been cultivated for centuries; many had been imported into England from the Middle East, India, and other parts of Europe. Pigeon fanciers formed clubs, and their birds were displayed and judged at shows. The pigeons were certainly something to behold; because they were cultivated solely for display, fancy pigeons had (and have) incredible extremes of form. Go to a fancy pigeon show today and it’s easy to see what attracted Darwin.

“The diversity of the breeds is something astonishing,” Darwin writes. It certainly was for a naturalist accustomed to looking at variation in nature, where the finest details of structure and function might separate one species from another. Applying the same eye to fancy pigeons must have felt like stepping from a darkened room into a sunlit afternoon. Darwin lists some of the points of variation in fancy pigeons: the shape of bones, the number of vertebrae and ribs, the proportion of facial features, the size of inner structures like the esophagus, the number and shape of wing and tail feathers, even the appearance of the eggs and the differences between males and females.

“Altogether at least a score of pigeons might be chosen, which if shown to an ornithologist, and he were told that they were wild birds, would certainly, I think, be ranked by him as well-defined species,” he points out.  Having established the tremendous variety in pigeons, he then mentions what makes these variations important: all of the breeds are all thought to descend from the rock pigeon Columba livia. This is the crux of why Darwin singled out fancy pigeons, aside from the personal affection he eventually acquired for them. Their incredible diversity arose from a well-documented history that was believed to travel all the way back to a single origin. They showed very clearly the radiating quality of evolution over time.

Darwin never argued that different breeds of fancy pigeons are different species, but his point raises the question: if we see such divergences occur under breeding, couldn’t they also happen in an analogous way in nature? In his typical roundabout fashion, Darwin gently points out at the end of the section the ridiculousness of seeing it in any other way. If naturalists insisted that fancy pigeon breeds all descended from a single species, “may they not learn a lesson of caution, when they deride the idea of a species in a state of nature being lineal descendants of other species?”

His question carries implicit criticism of naturalists who had for so long overlooked domesticated animals and plants as a rich source of information about biology—and as vivid evidence for the capacity of species to evolve under different conditions. Darwin himself had purchased and bred pigeons; he joined local fancying clubs and learned about the different breeds. Although his letters poke fun at pigeon-fanciers as odd men, their obsessive devotion to detail certainly resonated with his own.

Incidentally, in making his case for the evolution of pigeons, Darwin found himself arguing against the prejudices of breeders as well as naturalists. Pigeon fanciers were so fixated on the uniqueness and purity of each breed—which they referred to as “races”–that they did not easily accept the idea that all breeds came from the humble blue rock pigeon. In a text on pigeons written in 1886, fancier Edmund Star declared that the origin of fancy pigeons “is still open” despite Darwin’s efforts to define the rock pigeon as the sole source. “But while with his eye single to the purpose of that theory he satisfied the conditions and his followers, there remains reason for doubt,” Star wrote, and he gave as one piece of evidence the fact that the blue rock “exists in abundance at the very doors of the English, the most expert of breeders” and yet stubbornly remained the same.