104 Evolution and Adaptation 
The facts of observation show, that when a new variety 
appears its descendants are more likely, on the average, to 
produce proportionately more individuals that show the same 
variation, and some even that may go still farther in the same 
direction. If these latter are chosen to be the parents of the 
next generation, then once more the offspring may show the 
same advance; but little by little the advance slows down, 
until before very long it may cease altogether. Unless, then, a 
new kind of variation appears, or a new standard of variation 
develops of a different kind, the result of selection of fluctu- 
ating variations has reached its limit. Our experience seems, 
therefore, to teach us that selection of fluctuating variations 
leads us to only a certain point, and then stops in this direc- 
tion. We get no evidence from the facts in favor of the 
view that the process, if carried on for a long time, could 
ever produce such great changes, or the kind of changes, as 
those seen in wild animals and plants. 
VARIATION AND COMPETITION IN NATURE 
Darwin rests his theory on the small individual variations 
which occur in nature, as the following quotation shows : — 
“Tt may be doubted whether sudden and considerable 
deviations of structure such as we occasionally see in our 
domestic productions, more especially with plants, are ever 
permanently propagated in a state of nature. Almost every 
part of every organic being is so beautifully related to its 
complex conditions of life that it seems as improbable that 
any part should have been suddenly produced perfect, as that 
a complex machine should have been invented by man in a 
perfect state. Under domestication monstrosities sometimes 
occur which resemble normal structures in widely different 
animals. Thus pigs have occasionally been born with a sort 
of proboscis, and if any wild species of the same genus had 
naturally possessed a proboscis, it might have been argued 
