Man is not above nature, but in nature.

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

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.

The cell never acts; it reacts.

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.

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.

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.