Ernst Haeckel quotes:

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.

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.

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

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

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. Indeed, our so-called "educated classes" are to this day in total ignorance of the most important circumstances and the most remarkable phenomena which Anthropogeny has brought to light.

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.

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. Indeed, our so-called 'educated classes' are to this day in total ignorance of the most important circumstances and the most remarkable phenomena which Anthropogeny has brought to light.

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.

Man is not above nature, but in nature.

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

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.

An irrefutable proof that such single-celled primaeval animals really existed as the direct ancestors of Man, is furnished according to the fundamental law of biogeny by the fact that the human egg is nothing more than a simple cell.

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.

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

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.

Ontogeny re-capitulates phylogeny.

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

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. [This] clearly indicates the true place of man in nature, but it dissipates the prevalent illusion of man's supreme importance and the arrogance with which he sets himself apart from the illimitable universe and exalts himself to the position of its most valuable element.

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 'divine power' or 'moving spirit' within the cosmos itself ... All the wonderful phenomena of nature around us, organic as well as inorganic, are only various products of one and the same original force.

Politics is applied biology.

The cell never acts; it reacts.

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 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.

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).

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 bodily infirmity, were killed. Only the perfectly healthy and strong children were allowed to live, and they alone afterwards propagated the race.

In the course of individual development, inherited characters appear, in general, earlier than adaptive ones, and the earlier a certain character appears in ontogeny, the further back must lie in time when it was acquired by its ancestors.