In Darwin’s last chapter “Recap and Conclusion,” he argues that the principles behind his theory of evolution – that variation exists in nature, species engage in a struggle for existence, struggles for survival result in competition between species, natural selection preserves advantageous variations that cause the proliferation of those variations in subsequent generations, and these variations cause divergence of groups from their predecessors, forming new species resulting from descent with modification – are strong enough to fill in the gaps that may still remain. Darwin states at the beginning of his chapter, “That many and grave objections may be advanced against the theory of descent with modification through natural selection, I do not deny…this difficulty…that gradations in the perfection of any organ or instinct, which we may consider, either do now exist or could have existed…and, lastly, that there is a struggle for existence leading to the preservation of each profitable deviation of structure or instinct. The truth of these propositions cannot, I think, be disputed” (Darwin, 482).
Darwin’s argument about natural selection and variations happening slowly was convincing to me. He stated, “As natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modification; it can act only by very short and slow steps” (Darwin, 492). This is convincing because we don’t see variations of species in short periods of time, it takes several years before we see the different variations. Darwin’s principle of the struggle for existence was also convincing. He states that more individuals are born than can survive therefore species will compete and adapt in order to survive.