That man was Alfred Russel Wallace. When summarized, like most good scientific theories, the ideas of Danvin and Wallace are surprisingly simple. There are five major points. Living creatures have more offspring than can possibly survive. There is variation in these offspring.
Some variations give an advantage and some a disadvantage in an inevitable struggle for survival.
Nature will select the most fit variations to survive in this struggle and these variations will be the ones to pass on the favored offspring. In this way living things will change over time. Given enough time, these changes will be so great that whole new species of living things will appear on the earth. They made an immediate, a dramatic and a long-lasting impression on the world of science and of society. In these books he piled one piece of evidence on another to illustrate and to support his theory of natural selection.