Among questions bearing upon it but not directly attacking it has been the discussion of the individual difference. For example, are differences due to individual experiences ever inherited? Or are only inherent differences transmissible? What rôle is played by what one might call “normal,” relatively slight differences, and what by the “sports” and abnormal births in specific change? Do species under stress, and feeding on strange food or living in unaccustomed climates, betray any exceptional tendency to produce abnormality? Have there been, so to speak, storms and riots of variation in some cases? Can differences establish themselves while outer necessity remains neutral? Can variations amounting to specific differences in colour and form arise as a sort of play of the germ plasm and be tolerated rather than selected by nature? In what manner do normal differences arise? What happens to differences in cases of hybridisation? Here are sample questions that have been the seeds of splendid work and great arguments. Some of them were already under discussion in Darwin’s time; he was a pioneer in such explorations; many ideas of his have stood the test of time, and many suggestions he threw out have been disproved. When some casual “may be” of Darwin’s is examined and set aside, it is the custom of polemical journalists to rush about and proclaim to all who may be sufficiently ill-informed to listen that Darwin is “exploded.” Such explosions of Darwin are constantly recurring like gun-fire near a garrison town, and still he remains. None of these subsidiary questions affect the stability of this main generalisation of biology, the Theory of Natural Selection.