Initially Darwin outlined the inevitable challenges to his theory, and did so with an open mind, always freely admitting that his work was not indisputable. He ceded that he did not have enough concrete proof that species had indeed evolved as he theorized, and that there was no true geological evidence of progressive natural selection, but after ceding each point immediately responded with a rebuttal, reaffirming the validity of his own argument. Then, having acknowledged the opposition, he went on to argue all the points in favor of his conclusion, ranging from the variability of species and man’s own ability to selectively breed, to the geological factors that support different levels of variation in different environments. He always maintained that there were holes in his theory, and never defended it as the gospel truth, yet firmly argued that all the evidence pointed towards the verity of his deductions.
Perhaps the most convincing part of this argument is the initial segment wherein he addresses the challenges that will be posed against his work, since he uses it to definitively shut down as much opposition as possible before it has a chance to emerge. He knows that he will face a great deal of protest, but effectively faces it head on in a polite and persuasive manner. Conversely, that same section also contains the weakest point of his argument, which can be attributed to the uncertain nature of science. While his work cannot be definitively disproved, nor can he definitively prove it, for an attempt to claim as much would alienate his contemporaries. Thus, his counterpoints are reduced to an acknowledgement that the geological timeline is not perfect, and that even if they disagree with him other scientists cannot just tell him he is wrong without first supplying their own imperfect evidence.