EVOLUTIONARY THEORIES SINCE DARWIN 243 
that the earliest beginnings of any variation must 
be too slight to be useful, or as the term went, to 
have selective value. 
It has been noticed by a number of naturalists that 
certain animals seem to carry the development of a 
peculiarity altogether too far. It is seen for instance 
that in the Irish Elk, which has for some time been 
extinct, the horns were so enormous as to be a source 
of danger rather than of assistance to their owner. 
It was said that the tendency to produce heavy horns 
had gained, as it were, a sort of momentum, and that 
this impulse had carried the development beyond a 
safe limit. The Irish Elk became extinct because his 
horns were too heavy. During the Mesozoic period 
the reptiles grew too large. They seemed to have 
carried size to a point at which it became a danger 
instead of a help. They completely passed out of 
existence, leaving behind them only very much 
smaller reptiles. 
Eimer, of Germany, has based on facts like these 
his theory of Orthogenesis. He says that variations 
in animals are not indefinite and in every direction, 
but that they follow along clear and definite lines. 
These lines, in the case of the elk and of the Meso- 
zoic reptiles, developed too far, but ordinarily the 
effect of such a tendency is distinctly beneficial to 
the animal. It particularly assists in carrying on for 
