cause. It presupposes that individual organisms reveal variations which may be either more or less favorable to their preservation or to the preservation of the species to which they belong. Those individuals which show favorable variations would naturally survive in the struggle for existence (Origin of Species, 1858).
Darwin found the proof of his theory in the "intelligible thread" by means of which a vast array of facts can be combined. He did not regard his theory as a dogma, but rather as an instrument of research. He always insisted on tracing out the significance which a given character, function or organ possessed for the struggle for existence.—He regarded the problem concerning the origin of the variations by virtue of which natural selection takes place as a weakness in his hypothesis. He assumes the fact that such variations exist, and for the time being calls them "chance-variations," only meaning by this however that their causes are unknown. He takes a similar attitude to the problem of life in general.
Darwin's assumption that very small variations furnish a real advantage in the struggle for existence was perhaps an error. Hugo de Vries has quite recently undertaken to show that very important variational "leaps" ("mutations") may take place and that a new type may thus arise at once, which must then establish itself in the struggle for existence. It has become apparent, furthermore, that these mutational types are very tough. The contrast between the types and variations consequently becomes even sharper than Darwin, and especially the Darwinians, who have frequently been more dogmatic than their master, ever supposed.
Darwin saw no reason for regarding man an exception from the general biological laws. In his opinion the
