First appearing in 1866, Oecologie was one of the many neologisms of Ernst Haeckel, the leading German disciple of Darwin. Haeckel derived the new label from the same root found in the older word "economy": the Greek oikos, referring originally to the family household and its daily operations and maintenance. Haeckel suggested that the living organisms of the earth constitute a single economic unit resembling a household or family dwelling intimately together, in conflict as well as in mutual aid.

In his 1869 inaugural lecture as a professor at Jena, he also put an explicitly Darwinian border around the word: "the body of knowledge concerning the economy of nature [Naturhaushalt], . . . the study of all those complex interrelations referred to by Darwin as the condition of the struggle for existence."

The new term eventually replaced an older phrase "the economy of nature," first as "oecology" and then, after the International Botanical Congress of 1893, in its modem spelling as "ecology." In the broadest sense it was to be the study of all the environmental conditions of existence, or, as his translator later put it, "the science of the relations of living organisms to the external world, their habitat, customs, energies, parasites, etc."