This is the book that turned modern culture upside-down. Affecting not just science but the humanities, government and even theology, this thesis was the result of years of observational science by Darwin, during which he observed changes within species and extrapolated the information to mean that changes between species could occur. Non-theological abrupt appearance, the logic of which is now disputed by some evolutionary scholars, and evolution (biological/organic, biochemical/chemical, and cosmic/stellar) are the main features of Darwin's conjecture, and both have been thoroughly refuted by reputable scientists in the century-and-a-half since it was published. Nevertheless, it remains the backbone of modern science, psychology, anthropology and sociology due to many factors not covered in the book itself.
While Darwin was the first to poke holes in his own hypothesis, it was still taken up by many who saw how his dehumanizing speculations could be applied to 'racial purity' and social theory, to name but a few of its historical applications, for their own humanistic purposes. Moreover, honest evolutionists have gone on record very clearly about a non-theistic faith being the necessary foundation for their worldviews and lifestyles, and evolution provides the intellectual basis for just such a religion in secular humanism. But, since this book is still at the base of much of western civilization, understanding the concept can be helpful in ascertaining many of the evolution-based problems of society.
Now Christians know better, but a hundred years ago the faith of many was shaken by what seemed to be unequivocal refutation of the Bible's truth. Many people still labor under the assumption that whatever is taught in schools and colleges supersedes scriptural precedent. Still more don't know, understand, care, or want to upset the perceived societal status quo, and so choose not to speak out against evolution when basic knowledge of its claims could inform and solidify their faith. When an idea as influential as this is not checked it can undermine the morality, constitution, and collective faith of the nation.