Ecology is an interdisciplinary field that includes biology and Earth science. The word "ecology" ("Ökologie") was coined in 1866 by the German scientist Ernst Haeckel (1834–1919). Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology transformed into a more rigorous science in the late 19th century. Evolutionary concepts on adaptation and natural selection became cornerstones of modern ecological theory. Ecology is not synonymous with environment, environmentalism, natural history, or environmental science. It is closely related to evolutionary biology, genetics, and ethology. An understanding of how biodiversity affects ecological function is an important focus area in ecological studies.
Ecology is generally defined as the study of plants and animals in reciprocal relationship with their environment or external world. It appears possible that Hanns Reiter had used the term' Ecology' before Haeckel. As a science ecology is relatively a young branch of biology which deals with the interacting system of organisms and their environment. The term Ecology (old spelling Oekologie) is of recent coinage (E.Haeckel 1869) and has been derived from Greek words Oikos meaning house and Logos meaning the study. Therefore, ecology is the study of organisms in their natural home or habitat.