Many people are saying, this is the age of Aquarius. Many people are also saying this is the age in which we must express our concern for the biosphere or perish. Biosphere has such far-reaching connotations, however, that it is beyond the comprehension of most of us, including the great majority of those who have recently discovered it, and who so vigorously assert their willingness for deep personal involvement in efforts to save it.
With respect to human health and disease, I have found it useful to think of ecology at three levels of operation: (1) As it involves the biosphere. Admittedly there is an essential interrelationship among all things: everything has an effect on everything else. Unfortunately, I do not know how to formulate, much less solve, the infinite number of equations that would be required to handle this infinite number of variables. (2) As it involves macroecology, which I relate to man. In the sense that I am using it, macroecology includes those factors that have a demonstrably significant effect on man's external environment. The distinction between biosphere and macroecology (of man) is a device of communication that makes it convenient to select from the former those factors that have a more direct effect upon man and, thus, deserve priority in our concern. (3) As it involves microecology, which, as I am using the term, concentrates on those factors that affect man's internal environment.