The text features excerpts from the first edition of Charles Darwin's On the Origin of Species. Darwin expounded his theory of natural selection, arguing that species evolve through the gradual accumulation of favorable variations. The laws of variation are discussed, including the influence of external conditions, the use and disuse of organs, and the correlation of growth. Sexual selection and the imperfection of the geological record are also discussed, presenting examples of species variability and difficulties in classification.
Finally, Darwin addresses the geographical distribution of species and the importance of migration.

Darwin, C. (1859). On the origin of species.