Evolutionary theory is a scientific explanation for how species change over time through a process called natural selection. It suggests that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to their offspring. This gradual change can lead to the development of new species. The theory is supported by evidence from various fields, including genetics, paleontology, and comparative anatomy. Key figures in the development of evolutionary theory include Charles Darwin, who proposed the idea in the 19th century, and Alfred Russel Wallace, who independently arrived at similar conclusions.