THE 
AMERICAN NATURALIST. 
VoL. xx.—WAY, 1886.—No. 5. 
THE LIMITS OF ORGANIC EVOLUTION. 
BY H. W. CONN, PH.D. 
Ee theory of evolution implies a past, a present and a future. 
Since the time of Darwin the past and present of the organic — 
world have been studied with the result of showing that the his- 
tory has been one of evolution. Having now reached this con- 
clusion, and having discovered many of the laws of advancement 
in living nature, we are getting into a position where we may ' 
begin to study the future. It is the object of this paper to indi- 
cate certain limits in development toward which the organic 
world have long been tending. 
The idea of evolution implies that there has been a gradual 
tise in the scale of organisms from the lowest to the highest. 
But when paleontologists have attempted to show this gradual 
tise by a study of fossils they have had much less success than | 
the theory of evolution would lead us to expect. That there has p 
n a general advance from the earliest fossils in the Silurian until r 
now, seems unquestionable. But instead of being the most pal- 
pable result of study, this advance is so obscure as to cause sur- 
Prise to all who have attempted to make it out in detail. Darwin 
expressed his surprise at the lack of evidence, and the difficulties 
ve increased rather than decreased since he wrote. In some 
groups ther€ has been an undoubted advance; the vertebrates, for : 
instance, showing this in a marked manner. In a majority of 
Sroups, however, we do not find it, for while the animals have not 
in any case remained absolutely stationary, the development, as a — 
me has consisted chiefly in the increase and diversity of species - 
and genera. It is a matter of continual surprise to naturalists to 
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