Ontogeny re-capitulates phylogeny.

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.

Both of these branches of evolutionary science, are, in my opinion, in the closest causal connection; this arises from the reciprocal action of the laws of heredity and adaptation.

Man is not above nature, but in nature.

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

Civilization and the life of nations are governed by the same laws as prevail throughout nature and organic life.

By ecology we understand the total science of the connections of the organism to the surrounding external world.