It is true that Darwin cannot completely prove evolution to be 100% true, but he does make many very good points on why he believes it is correct. He first brings up evolution due to geographical distribution. He talks about how species with similar genomes are found with different traits on different continents. So this shows that the species all came from a common ancestor but altered their traits over time in order to thrive in their home environments (Quammen, Pg. 484). Another argument he makes is that if each species really was independently created, why do traits differ so much in those with the same genus? (Quammen, Pg. 494) He then speaks about how evolution does not come with drastic changes overnight, but instead how small changes are made over an extended period of time (Quammen, Pg. 492). He then sites a specific example of successful evolution. He talks about how the bones in the hands of humans, bats, porpoises are all identical. So although he cannot prove evolution as completely factual, he does provide many points on why it is more than likely correct.
Many points of Darwin’s argument where convincing, but some were more convincing than others. The most convincing was the argument of geographical distribution. The fact that species with the same genomes have different traits in different parts of the world proves that a common ancestor must have been shared with all the species but they slowly modified to inherit traits that allowed them to survive and thrive in their given environments. I believe one of his less convincing arguments was how different species with the same genus vary so much physically. I found it almost counterintuitive to his argument that each species was not independently created. But I believe it still adds to his argument that very different species can share the same genus.