The Origin of Species Chapter 9 Part 1 - Hybridism

In which the curious phenomena of hybrid sterility are examined with a careful distinction between the imperfect union of distinct species and the functional impotence of their hybrid progeny, revealing a gradation of fertility that defies simple classification. The laws and causes of this sterility are explored through manifold botanical and zoological experiments, suggesting that such reproductive barriers are incidental upon differences in reproductive systems rather than being specially endowed to prevent the mingling of species.