Natural selection theory is one of Darwin’s prime arguments, in that a species will accumulate traits with each passing generation due to traits that help the species survive being favored in reproduction and therefore being reproduced in the offspring and descendants, whereas traits detrimental to survival of the species will get its members killed before they can pass on their genetic material. Dominant species are able to reproduce and populate in large groups (Darwin, 492) with natural selection being possibly more apparent due to greater and more varied divergences in character in members of the population. Traits such as webbed feet are ideal for species like ducks to survive in water, so webbed feet will become more pronounced and apparent over time as these birds evolve to survive in that sort of environment (Darwin, 493). Throughout incredibly ‘long intervals of time’ and multiple generations ‘old forms are supplanted by new forms’. In addition, fossil records show ancient versions of creatures that are similar to ours today but clearly are at a previous point in evolution, showing traits that not as developed as their modern counterparts and traits that no longer exist due to having eventually been bred out. (Darwin, 497).
Darwin also refers to the finches of the Galapagos Islands in his studies, observing how close in appearance and form the two species of birds were, but how their beaks had become differently shaped and functioning along with other traits, despite living in the same general geographical area. Darwin theorized that due to competition and the environment, one group of finches began to adapt their feeding habits differently to survive, with members of the species that did not share those mutations ideal to this new lifestyle dying off, creating a different subspecies (Darwin, 499).
I think the finches are the most convincing example, as it shows this process of evolution and natural selection happening in a relatively short amount of time (as far as the ecosystem goes). The variation of beaks from island to island and the similarities between the birds shows how gradual and subtle these adaptations can be, and especially how environment affects members of what was once a single, monolithic species into being multiple different variations.