THE UNIQUE MAMMAL 19 



tionship between organism and environment generally. For the 

 sake of brevity this discussion may start with the bald and con- 

 densed proposition that the relationship between any organism 

 and its environment is particular, continuous, indissoluble, and 

 reciprocal. It is particular because each individual organism has 

 its own environment peculiar to itself and not fully shared 

 with any other organism. Adam Short, six feet three inches tall, 

 has a definitely different environment at all times and places 

 than does Hiram Long, who is five feet tall and nearly as broad. 

 All conceivable differences between individual organisms, and 

 there is an indefinitely large number of such differences, neces- 

 sarily entail associated differences in the environment that is 

 particular to the individual. The relationship is continuous be- 

 cause at no time while life exists can organism and environment 

 be separated. It is indissoluble because organisms are dependent 

 for their very existence upon energy and matter derived from 

 the environment. Finally the reciprocal characteristic of the 

 organism-environment relationship arises because each individ- 

 ual organism is continually altering its environment in some 

 degree even if only very slightly, and in turn is itself being 

 altered by the environment. For example in running across a 

 snow-covered field a rabbit alters the field at least to the extent 

 of the tracks it leaves; and, conversely, after this simple event 

 the rabbit itself is a different rabbit from what it was before 

 or would have been if the field had been, let us say, grass- 

 instead of snow-covered. This is designedly a very simple, and 

 in that sense "far-fetched" example of an extremely complex and 

 important part of biology. What it leads to is the broad principle 

 that, in varying degrees from species to species, all animals 

 both choose and make their environments. In other words the 

 organism-environment relationship is never a completely hap- 

 hazard or random connection, such as that between pennies and 

 their environment when say 50 perfect and physically identical 

 pennies are tossed together. In the latter case the behavior of 

 the pennies is wholly determined by the action of the environ- 



