Darwin states that his theory had gaps but nonetheless the argument still is solid and heavily based in evidence (Darwin, 484). He continues to argue four main principles that support his theory; variation in nature, struggle for existence within and between species, and the survival characteristics favored within natural selection. The first highlights the prolific nature of trait changes within a species, such as Darwin saw with the finches that adapted different shaped beaks depending on what they ate. The second explanation, struggle for existence within a species, can also be explained using the finches. Without the beak adaptations, these birds would have not been able to survive and reproduce, allowing only those with the trait to pass on their genes. For specie struggles with other surrounding species, consider the predator and prey relationship. For prey which evolved camouflaging techniques, they outlived others and were able to pass on their traits. The final principle can be seen in all of the other three, as it is natural selection that allows for the progression of a particular trait from generation to generation. Consider the giraffe, which had to evolve to have such an abnormally long neck for fighting and eating purposes and only those with that trait lived to pass on their genes.
The final argument is the most convincing and logical to me. Natural selection acts almost as a force, no different than gravity. It is most commonly dictates the progression of a species, but it can be overcome with enough effort. Humans have begun to take part in our own evolution, with scientific progressions allowing for certain diseases to be survived and others possibly being alleviated all before the child’s birth. Natural selection is most convincing when it also takes into consideration the role humans have begun to play in our own evolution.