Two arguments that Darwin imposed to try and persuade people to believe his theory of evolution were the ideas regarding hybrids and geographical and climate impacts on species. Hybrids were mentioned extensively, mostly regarding how they were generally infertile (p. 484). However, Darwin explains that most of the evolution that occurred was not because of two different animals mating and creating a hybrid, instead it was the good survival traits from the parents that were passed down to offspring that caused evolution. Darwin thinks that rather than focusing on hybrids, people should focus on the increased fertility of animals as evolution occurs because more desirable traits are able to be passed down from parent to offspring. Supplementing this argument is Darwin’s argument regarding geographical and climate impacts and barriers. Darwin states that he understands it’s difficult for people to imagine and understand such a concept because at that time, humans knew little about previous climactic and geographic conditions (p. 485). However, after acknowledging this downfall, he goes on to explain how geographic isolations and barriers have caused completely unique and different traits in animals that live in specific places. This is clear in research regarding animals in Madagascar and the Galapagos Islands, as extremely unique animals are able to develop due to the complete and utter isolation of the islands (p. 494). This uniqueness and variability of animals on islands highlights the idea of evolution because the traits these animals develop are completely unique to where they live, but they are still derived from a common ancestor from the mainland areas.

Overall, I think the argument regarding the geographic and climactic effects on evolution is one of the weaker arguments, solely because during Darwin’s time he didn’t know what we know now, so his argument wasn’t heavily supported by evidence. I think the fertility and mating argument is probably the strongest because he proved aspects of it in his lab with the peas and flowers that he crossed and he was able to somewhat understand the science behind genetics and natural selection which leads to evolution.


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