Darwin argued that through natural selection, there is proof of evolution. Darwin pointed out the appearance of the natural selection successors of previous animals that we have fossils of. An example which he uses is armadillos. He brings attention to the fact of that giant sloths bones and armadillo bones are fossilized and yet are extremely similar to present day animals. This is even more exemplified when Darwin discovers that the proximity of these ancient, slightly different bones are all consolidated in the same area where armadillos and sloths inhabit. Darwin also focused on how there are multiple relatively similar looking birds, all seemingly dervivitive of a similar ancestor bird. When Darwin started focusing on this, he also noticed that all of these birds seem to differ one another for natural reasons, not just for cosmetic reasons. Eventually, Darwin came to the conclusion that there are certain genes that are advantageous for animals which they seem to keep depending on the type of environment they live in.
The argument the most convincing for me was the initial findings of Darwin. With finding the same species in specific spots that their ancestors lived with minor changes in the way of their bone structure begs to be inquired as to how the current animals such as armadillos are similar yet different. When these findings were discovered in a remote environment that hasn’t spread, Darwin was able to determine that the animals staying in on environment over time evolve to match the conditions in which they find themselves.