From Pigeons to Potatoes
All the research Darwin undertook in 40 years at Down House revolved around a single grand theme: evolution by natural selection. In at least 16 books and many papers, Darwin explored variation and adaptation. He worked tirelessly to figure out how natural selection had acted on variation to produce the marvelous adaptations he saw.
But in many cases he couldn't do this directly. Extended studies of wild nature--measuring and tracking minute changes in fur, feather or flower over generations--were unimagined by any naturalist of the period. So instead Darwin often turned to domesticated species--manageable and well-documented groups that he, or the experts he knew, could breed and shape. Pigeons, rabbits, cabbages, gooseberries--these would be a major object of study and his window into the workings of selection.
Charles Darwin, Pigeon Fancier
The birds on display are all types of fancy pigeons Darwin raised at Down House. Raising the animals--all these breeds are descended from the rock dove--was a popular hobby of the day. Breeders competed to produce varieties with a particular color or beak shape, and Darwin did the same. At one point, his flock grew to 90 birds.
But Darwin was interested in evolution, not pigeon shows. He wanted a sense of how much variation existed within a single type of animal in nature. Breeding animals--selecting and perpetuating desired traits--was a sped-up version of the process that gave rise to new species in nature, he thought. Much more than a hobby, Darwin's pigeon work was a way to demonstrate how dramatic the effects of selection could be.
A Special Group
"Believing that it is always best to study some special group, I have . . . taken up domestic pigeons," Darwin wrote. There are about 200 named breeds; those Darwin raised provided him insight into the workings of selection.
Plant a Cabbage, Get a Brussels Sprout
Variability in the cabbage family interested Darwin. The wild cabbage, he knew, had given rise to very different-looking varieties, including Brussels sprouts, broccoli, and kale. What accounted for this diversity? "The explanation is obvious," Darwin wrote. Because we humans eat the leaves of these plants, farmers had been selecting the "many useful variations in their leaves and stems" since prehistoric times. Such strong selective pressure produced those distinct shapes.
Birds of a Feather
Darwin was always ready to learn from experts, both amateurs and scientists. He belonged to several workingman's pigeon clubs as well as the exclusive Philoperisteron Club, whose members were voted in.
More Than Skin Deep
Darwin included these diagrams of pigeon skulls in his major work on domestication. The color, shape and placement of feathers are the obvious markers of pigeon breeds, but the skeletons underneath differ, too. Had these skulls belonged to wild birds, Darwin thought, they would be considered different species. And if artificial selection could produce such diversity over decades, what might natural selection produce over millions of years?