The succession of individuals, connected by reproduction and belonging to a species, makes it possible for the specific form itself to last for ages. In the end, however, the species is temporary; it has no "eternal life." After existing for a certain period, it either dies or is converted by modification into other forms.

Mental differences between the lowest men and the animals are less than those between the lowest and the highest man.

Man is not above nature, but in nature.

Phylogeny and ontogeny are, therefore, the two coordinated branches of morphology. Phylogeny is the developmental history [Entwickelungsgeschichte] of the abstract, genealogical individual; ontogeny, on the other hand, is the developmental history of the concrete, morphological individual.

The nucleus has to take care of the inheritance of the heritable characters, while the surrounding cytoplasm is concerned with accommodation or adaptation to the environment.

The whole of organic nature on our planet exists only by a relentless war of all against all. ... The raging war of interests in human society is only a feeble picture of an unceasing and terrible war of existence which reigns throughout the whole of the living world.

There is no doubt that the course and character of the feared 'European war'... will become the first world war in the full sense of the word.