The Making of Species 
In either of these circumstances natural selection 
will be an inhibitory force, for if the normal 
organism is perfectly adapted to its environment, 
all variations from the type must be unfavour- 
able, and natural selection will weed out the 
individuals that display them. No careful 
student of nature can maintain, either that all 
animals are perfectly adapted to their environ- 
ment, or that this never changes. Hence those 
who deny that natural selection is a factor in the 
making of species, assume the second set of con- 
ditions, that species develop in certain fixed 
directions, being impelled either by internal or 
external forces. How far these ideas are founded 
on fact we shall endeavour to determine when 
speaking of variation. It must suffice at present 
to say that even if any of these views of ortho- 
genesis be established, natural selection will have, 
so to speak, a casting vote, it will decide which 
series of species developing along preordained 
lines shall survive and which shall not survive. 
Thus we reach by a different line of argument 
the conclusion we arrived at in the last chapter : 
namely, there is no room for doubt that natural 
selection is a factor in the making of species. 
We must now pass on to the second class of 
objections, those which are urged against the all- 
sufficiency of natural selection. So numerous 
are these that it is not feasible to consider them 
all. A brief notice of the more important ones 
34 
