Environment the aggregate of all the external conditions and influences affecting the life and development of an. A branch of science concerned with how living organisms are connected to each other and to their environment; derived from the greek oikos, household or living place. The organisms of a particular habitat, such as a pond or forest, together with their physical environment. Depending upon their purpose scientists, resource managers or policymakers consider a lake, a watershed or an entire region an ecosystem. Development which meets the needs of the present without compromising the ability of future generations to meet their own needs. Each species operates within environmental limits beyond which survival is not possible; if things are too cold, hot, dry, wet--death results; if change is slow enough a species may adapt and survive. 2 billion + years in the making of the earth. 2 million +\- years in human evolutionary development.