244 THE MEANING OF EVOLUTION 
a time the variations which have not yet become use- 
ful to the animal. It has always been difficult on 
Darwinian principles to understand how the begin- 
nings of the useful variations could be selected before 
they were strong enough to be of actual value to the 
animal. This tendency to variations in certain di- 
rections instead of at random would account for such 
early development. This theory of Orthogenesis has 
not figured very strongly in the history of the move- 
ment, but it recurs at intervals. 
Both in America and France there is a constant 
tendency on the part of zodlogists to return to the 
Lamarckian idea that it is the use of an organ that 
develops it, its disuse that makes it fade away. This 
is undoubtedly true of the individual, and although 
Weissman insists that it is useless to the species as a 
whole, many zodlogists are slow to relinquish entirely 
the idea that somehow these favorable developments 
become reproduced in the offspring. 
Professor Cope, the American paleontologist, was 
a strong believer in the effect of activity, both upon 
the individual and upon his descendants. He believed 
that the insistent beating of the foot of an animal 
upon the hard soil of the drying Tertiary plateau, 
had influenced the production of a firmer nail, which 
spread around the entire end of the toe and made 
the hoof of the ungulate. He believed that the use 
