100 JOURNAL OF SCIENCE. 
according to some predetermined standard; or it may be 
unconscious, as when the owner of a flock simply kills off the: 
worst or wildest individuals without any thought of altering the 
breed. Unconscious artificial selection is not confined to human 
actions, but is also found among plants and animals. The 
difference between natural and artificial selection must be clearly 
comprehended, for, as we shall see, both are important factors in 
the study of politics. Natural selection is a selection taking 
place, as it were, by and among the individuals themselves ; it 
is an internal principle, and may be called zztrinsic selection. 
Artificial selection, on the other hand, is an arbitrary selection 
from outside, and may be called ertrinsic selection. The great 
variety we find among wild flowers is due to both forms of 
selection combined—the intrinsic selection among the plants 
themselves, and the unconscious extrinsic selection of the insects 
that fertilise them. In garden flowers we see -the result of 
methodical extrinsic selection by man. 
Another point, very important for you to notice, is that the 
principle of selection does not necessarily lead to improvement. 
If we consider a limited district, such as an island, it is plain 
that in course of time, if the conditions of life remain constant, 
an almost exact equilibrium between the different plants and 
animals inhabiting it will be attained. The principle of natural 
selection, always acting in the direction of perfect mutual adap- 
tation, will in time bring it about; and then, as no further 
modifications would be beneficial, none will be preserved—the 
organisms will remain stationary. But this stationary character, 
you must observe, only obtains while the conditions of life 
remain the same; if any change takes place, the adaptations can 
no longer be perfect, and further modifications will be bene- 
' ficial. If the change is such that the conditions of life become 
‘harder, then the organisms must become more specialised ; 
they must, as we call it, progress. But if, on the other hand, 
the change is such that the conditions of life become easier, the 
effect will be just the opposite—the organs will become more 
generalised, and the organisms will degenerate. I will illustrate 
this by an example. Suppose an island to be inhabited by 
hares, which are preyed upon by sheep-dogs, and that an equi- 
librium in speed has been arrived at by which both main- 
tain their relative numbers. If now greyhounds are intreduced 
it is evident that the conditions of life with regard to the hares 
will be harder, and as only the fleetest will escape, all the hares 
on the island, in the course of some generations, will become 
fleeter—that is, more specialised. But suppose that, instead of 
greyhounds having been introduced, all the sheep-dogs were 
removed, so that there were no dogs at all on the island, it is 
evident that the conditions of life would now: be easier; the 
fleet would have no advantage over the slow, and the whole race 
would, to some extent, lose their special characteristic of swift- 
ness—they would degenerate. 
Under different circumstances, sometimes physical structure, 
