"...All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation, or the enunciation of general propositions, and the mere putting together and separating objects more or less alike. But I must explain my meaning more fully..." This re-print of Charles Darwin's 1859 publication of "On The Origin of Species" has been carefully formatted to improve readability and to ensure that the page numbers match, as closely as possible, the original table of contents and index for quick referencing and scholarly quotation of the author's 'First Edition'.