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 degree of psychic activity, a superior stage of development.

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 poetic imagination; knowledge, on the other hand, originates in the reasoning intelligence of man. Science has to pluck the blessed fruits from the tree of knowledge, unconcerned whether these conquests trench upon the poetical imaginings of faith or not.

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.

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 framework of organic nature.

Man is not above nature, but in nature.

I established the opposite view, that this history of the embryo (ontogeny) must be completed by a second, equally valuable, and closely connected branch of thought - the history of race (phylogeny). 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... 'ontogenesis is a brief and rapid recapitulation of phylogenesis, determined by the physiological functions of heredity (generation) and adaptation (maintenance).

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