As our mother-earth is a mere speck in the sunbeam in the illimitable universe, so man himself is but a tiny grain of protoplasm in the perishable fr….

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

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 onl….

Man is not above nature, but in nature..

Politics is applied biology..

The cell never acts; it reacts..

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

It is, however, a most astonishing but incontestable fact, that the history of the evolution of man as yet constitutes no part of general education. ….

The real cause of personal existence is not the favor of the Almighty, but the sexual love of one's earthly parents..

In the course of individual development, inherited characters appear, in general, earlier than adaptive ones, and the earlier a certain character app….

Ontogeny re-capitulates phylogeny..

Nothing is constant but change! All existence is a perpetual flux of "being and becoming!" That is the broad lesson of the evolution of the 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..

The succession of individuals, connected by reproduction and belonging to a species, makes it possible for the specific form itself to last for ages.….

Both of these branches of evolutionary science, are, in my opinion, in the closest causal connection; this arises from the reciprocal action of the l….

We are compelled by reflection to recognize that God is not to be placed against the material world [as in Christianity], but must be placed as a 'di….

Where faith commences, science ends. Both these arts of the human mind must be strictly kept apart from each other. Faith has its origin in the poeti….

Among the Spartans all newly born children were subject to a careful examination or selection. All those that were weak, sickly, or affected with any….

An irrefutable proof that such single-celled primaeval animals really existed as the direct ancestors of Man, is furnished according to the fundament….

Man is not distinguished from [the animals] by a special kind of soul, or by any peculiar and exclusive psychic function, but only by a higher degre….

Phylogeny and ontogeny are, therefore, the two coordinated branches of morphology. Phylogeny is the developmental history [Entwickelungsgeschichte] o….