Darwin used the fancy pigeon to take the theory of Natural selection into action and studied the way that different variations affect the individual's survival and reproduction. Specifically choosing Pigeons because of the variety in both appearance and behavior.

Darwin was fascinated with the variety of colors and shapes in the orchid family, conducting multiple observations, field experiments, and dissections. which led to him concluding that the orchid's genetic development was the result of insect pollination, which increased its genetic fitness and diversity needed for natural selection.

Darwin became fixated on barnacles, conducting multiple deep focused research on them, as well as dissections and classifications, and writing about them from 1846 to 1854. his research plays a huge role in his theory of speciation. classifying barnacles in a theoretical framework  and trying to fit it into his theory of evolution by comparing barnacle larvae to adults and how similar they are to crustaceans.