This 1907 work by Vernon L. Kellogg contains a fascinating discussion of the contemporary scientific criticism of the Darwinian selection theories, together with a brief account of the principal and other alternative theories of species-formation. Written for the sake of presenting simple and concise information to students of biology (as well as to general readers), this book is a readily accessible treatise on the subject and, as such, is recommended for anybody with an interest in Darwinism. Vernon Lyman Kellogg (1867 - 1937) was an American entomologist and evolutionary biologist. Many vintage texts such as this are increasingly hard to come by and expensive, and it is with this in mind that we are republishing this volume now in an affordable, modern, high-quality edition. It comes complete with a specially commissioned new biography of the author.