THE SELECTING POWER OF ENEMIES 43 
Matter.—Here, a unit of living matter is 
used in the sense of a single individual, one of 
many which, collectively, form a species. If 
examination be made of its environment, no 
matter which factor be chosen for observation, 
it will be found to be definitely bounded, in 
spite of the factor not being homogeneous. 
During a definite time—this must be taken 
into account—a plant occupies a definite quan- 
tity of space, it takes from the soil a definite 
quantity of mineral matter and receives a 
definite amount of sunlight. 
A single animal wandering on a mountain- 
side, climbs up and down to definite heights 
above sea-level. 
This power of being able to adapt itself to 
the diversities of its environment, within limits, 
is a property of all living matter. 
The Environment of a Species.—If the en- 
vironment of a unit is defined, then the en- 
vironment of a collection of units, a species, 
must be definite. 
In the case of sexual dimorphism and other di- and 
poly-morphisms, the environment of the species would be 
the environments of the several types of individuals added 
together: the defined environment of the male added to 
the defined environment of the female, &. This addition 
is necessary because the environment of the several] types 
of individuals is not identical, although each is defined. 
