PART I

            § 1. On variation under domestication, and on the principles of selection 

            § 2. On variation in a state of nature and on the natural means of selection 

            § 3. On variation in instincts and other mental attributes 

            PART II

            § 4. and v. On the evidence from Geology. (The reasons for combining the two sections are given in the Introduction) 

            § 5. Geographical distribution 

            § 6. Affinities and classification 

            § 7. Unity of type in the great classes 

            § 8. Abortive organs 

            § 9. Recapitulation and conclusion