Down House was in good orchid country; native species bloomed everywhere. This abundance delighted Darwin, who saw in the "wonderful creatures" a perfect case of natural selection at work. He recognized the intricate shapes of orchid flowers for what they were: adaptations that allowed the orchids to receive their insect pollinators as a lock receives a key.

Darwin's approach, as always, was simplicity itself. Armed with empty jars and biscuit tins, he roamed the woods near Down, digging up orchids and taking them home to dissect. He probed some of the flowers with a pencil, mimicking the action of an insect. Observing a pollen mass stuck to his pencil point, perfectly positioned to fertilize the next orchid, he realized that the flowers and the insect pollinators had evolved together. As evidence for the adaptations resulting from natural selection, Darwin wrote, "I have found the study of Orchids eminently useful."