5 *7 
The treatment of imperfect organs which we have been 
considering arises from the limitation which Natural 
Selection places upon the evolution of progressive organs 
and organisms—a limitation which is the peculiar feature 
of that theory. According to this view, every stage of 
progress must have been of vital importance to the race : 
it must have determined the issue between life and death 
of the individuals composing a species. 
“Nascent organs, though not fully developed, are of high service 
to their possessors, and are capable of further development.”— 
(.Descent of Man. 2nd ed., ft. 72.) 
“As Natural Selection acts by life and death—by the survival of 
the fittest and by the destruction of the less well-fitted individuals— 
I have sometimes felt great difficulty in understanding the origin or 
formation of parts of little importance.”—(Origin of Sftecies. ft. 736.) 
Speaking of cases where slight (because initial and 
afterwards finely graduated) improvements are concerned, 
Mr. Romanes says :— 
“ Unless, at every stage of their progress, they were matters of life 
and death, they could not have been produced by the unaided 
influence of Natural Selection.”—(Contemporary Review, vol. Ivi., 
ft. 234.) 
This limitation has a two-fold significancy. Those who 
believe that no evolution can take place except in con 
nection with Natural Selection, are bound to maintain that 
each step of progress, however slight, must be a matter of 
life and death. Those w r ho believe that Natural Selection 
only co-operates with other laws of nature, in an inter 
mittent fashion, suppose that for this evolution of the 
progressive organ the interposition of Natural Selection is 
not required at every stage. 
“It is surely conceivable that, in many cases where slight (because 
initial and afterwards finely graduated) improvements are concerned, 
such improvements need not have been, in every stage of their 
ftrogress, matters of life and death to the organisms presenting them.