Final answer:
Key contributors to evolutionary theory prior to 1859 include Jean Baptiste Lamarck, who proposed that species change over time; Charles Lyell, whose geological insights implied a much older Earth; and Thomas Malthus, whose essay on population influenced Darwin's natural selection concept.
Step-by-step explanation:
Before Charles Darwin's seminal work in 1859, several key people contributed to the development of evolutionary theory. One such figure was Jean Baptiste Lamarck, a French naturalist who proposed that species change over time. Although Lamarck's mechanism of inheritance of acquired characteristics was incorrect, he paved the way for future evolutionary thought. Another major influence on Darwin was Charles Lyell, an English geologist whose work suggested Earth was much older than previously thought, which was a fundamental concept for evolution. Additionally, Thomas Malthus, an English economist, posited that population growth is checked by famine and disease, an idea that helped shape Darwin's understanding of natural selection.
In parallel to Darwin, Alfred Wallace independently worked on and formulated a theory of evolution by natural selection. His writings prompted Darwin to publish On the Origin of Species. The two scientists' independent discovery of similar evolutionary mechanisms underscores the robustness of the theory they developed.