1.Darwin had many arguments about natural selection. Some very convincing, others not so much. His studies that he made were a different time. So looking back on what we know now we can analyze his arguments. One of his arguments was different species being absorbed to make some resemblance of their parents into each other by successive crosses. Darwin goes on to say “New species have come on the stage slowly and at successive intervals; and the amount of change, after equal intervals of time, is widely different in different groups. The extinction of species and of whole groups of species, which has played so conspicuous a part in the history of the organic world, almost inevitably follows on the principle of natural selection; for old forms will be supplanted by new and improved forms” (Darwin P.496-497). Through the amount of change, species change improving through time. But showing traits of what is preserved while evolving.
2.One of the most convincing arguments by Darwin was geographical distribution. Organic beings spread out through time. Starting from one place to another, adapting to the environment that is different. Darwin states “We can see why there should be so striking a parallelism in the distribution of organic beings throughout space, and in their geological succession throughout time; for in both cases the beings have been connected by the bond of ordinary generation, and the means of modification have been the same” (Darwin P.498). With the migration of others spreading geographically we can see the resemblance of many things.