The 19th century held a lot of scientific progression, most notably the development of evolutionary theory and the new understanding of energy and the laws that govern it. While both were undoubtedly important scientifically, Darwinian evolution had a more profound social impact and contributed more to our scientific progression.
The idea of evolution was being discussed long before Darwin came onto the scene; Lamarck's treatment of the new field of biology included a "chain of being" describing an inherent drive to evolve upwards along a linear path, with the culmination of evolution naturally falling upon mankind. This was a good start because it included the basic ideas and accounted for variation and mutation, but fell short because the upward movement would naturally leave gaps in the chain at the bottom, therefore making the theory dependant on the idea of spontaneous generation. .
The next major breakthrough in understanding the history of life was Lyell's geological contributions, and his argument that organisms were far from being driven upwards, rather, being geological markers in time and having natural prevention of much improvement or deterioration within a species. While touring South America he was gratified to notice that oftentimes species would be differentiated due to the physical and climactic geographies of a region. He also recognized the great challenges placed on a species to survive, citing that adaptation could be dangerous according to his model of constantly shifting geologic factors. Lyell was one of the first to provide a satisfactory explanation and mechanism of extinction and furthermore linked many of the relevant factors to make evolution an integral part of the discussion about the history of life. Lyell had made an initial offering, but he continued to contribute to the quest for understanding evolution by alerting his colleague Darwin to things of interest and passing on his ideas and criticisms.
