Man has been engaged from the start of his existence on this earth in a continuous struggle with the numerous hostile animate and inanimate forces present in his natural environment.1 While not all human subspecies successfully survived the repeated and severe environmental changes, those which did are the products of biologic adaptation processes, involving many successive generations and extending through many thousands of years.
In sharp contrast to these gradually developing changes occurring in the natural environment and in man in the past are the rather acute and fundamental alterations which modern man has been making in his environment during the last century by the addition of numerous and in part new inanimate physical and chemical agents. Many of them possess distinct and powerful biologic properties. A new and continuously changing artificial environment has thereby been created which has been superimposed upon the natural one. Through these events not