British naturalists Charles Darwin and Alfred Russel Wallace both set out on epic adventures to study various species and their development. They gathered evidence on the variation among individual members of a species, the relationships among species, and the patterns of geographic distribution across many species. Based on such evidence, they independently came to the same revolutionary conclusions: species change over time by means of natural selection, and species descend from other species.
This video was very clear and worked well for my class. ~Trout, KSD