"Evolution made plain by John Mason" is a concise popular science pamphlet written in the early 20th century. It is a scientific publication that introduces the theory of evolution in plain language, explaining how natural selection and other natural laws account for the development of all life, including humans. The book defines what evolution is and is not, separates it from common misconceptions, and surveys geological time and the fossil record to show a progression from simple to complex forms. It marshals anatomical and embryological evidence (homologies, vestigial organs, and stages of development), discusses “connecting links,” and compares humans and apes alongside early human fossils. It explains natural selection, variation, artificial selection, and the idea of mutations, then extends these ideas to social thought, urging free inquiry and tolerance while criticizing biblical literalism and popular objections. In its final sections it applies heredity and environment to human progress, argues for the primacy of the common good, and controversially advocates eugenic measures, calling for improved environments and responsible reproduction as the path to future advancement. (This is an automatically generated summary.)