OUTLINE OF BIOLOGICAL PROGRESS 17 
sification of Aristotle, founded on plan of organization, by a 
highly artificial one, founded on the incidental circumstance 
of the abodes of animals—either in air, water, or on the earth. 
The Arrest of Inquiry and its Effects—Thus, natural 
history, transferred from a Greek to a Roman center, was 
already on the decline in the time of Pliny; but it was des- 
tined to sink still lower. It is an old, oft-repeated story how, 
with the overthrow of ancient civilization, the torch of learn- 
ing was nearly extinguished. Not only was there a complete 
political revolution; there was also a complete change in the 
mental interests of mankind. The situation is so complex 
that it is difficult to state it with clearness. So far as science 
is concerned, its extinction was due to a turning away from 
the external world, and a complete arrest of inquiry into the 
phenomena of nature. This was an important part of that 
somber change which came over all mental life. 
One of the causes that played a considerable part in the 
cessation of scientific investigation was the rise of the Chris- 
tian church and the dominance of the priesthood in all intellec- 
tual as well as in spiritual life. The world-shunning spirit, 
so scrupulously cultivated by the early Christians, prompted 
a spirit which was hostile to observation. The behest to 
shun the world was acted upon too Hterally. The eyes were 
closed to nature and the mind was directed toward spiritual 
matters, which truly seemed of higher importance. Pres- 
ently, the observation of nature came to be looked upon as 
proceeding from a prying and impious curiosity. 
Books were now scarcer than during the classical period; 
the schools of philosophy were reduced, and the dissemina- 
tion of learning ceased. The priests who had access to the 
books assumed direction of intellectual life. But they were 
largely employed with the analysis of the supernatural, 
without the wholesome check of observation and experiment; 
mystical explanations were invented for natural phenomena, 
2 
