34 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
physicochemical world, have tried to adduce a definite causomechani- 
cal explanation of orthogenesis. The best and most comprehensive 
types of this explanation are those essentially Lamarckian in principle, 
in which the direct influence of environmental conditions, the direct 
reactions of the life stuff to stimuli and influences from the world 
outside, are the causal factors in such an explanation. But while 
every naturalist will grant that such factors do change and control 
in a considerable degree the life of the individual’, most see no mechan- 
ism or means of extending this contro] directly to the species.” 
The above-quoted paragraphs from Jordan and Kellogg will 
serve to place before the reader the general ideas involved in the 
orthogenesis conception. A brief account of the various special 
theories of orthogenesis follows: 
Carl von Négeli’s ideas of orthogenesis involve a belief in a sort of 
mystical principle of progressive development, a something, quite 
intangible, that exists in organic nature, which causes each organism, 
to strive for or at least make for specialization or perfect adaptation. 
This idea of an inner driving and directing force reminds one of the 
“entelechy” of Driesch, or Bergson’s “creative evolution.” Néageli 
believed that animals and plants would have developed essentially 
as they have without any struggle for existence or natural selection. 
This form of orthogenesis theory, then, is alternative to natural 
selection. 
Theodore Eimer’s theory of orthogenesis is more scientific and less 
mystical than Nageli’s. He believed that lines of evolution were not 
miscellaneous and haphazard, but were confined to a few definite 
directions, determined at their initia] stages not by natural selection 
but by the laws of organic growth, aided by the inheritance of acquired 
characters. A new character makes a beginning as would the first 
step in a slow chemical change, or series of such changes, and it must 
go through to a fixed end, under given conditions, just as surely as does 
the chemical process. Only when a given character or line of evolu- 
tion results in the production of a very positive advantage or dis- 
advantage to the species does natural selection step in to interfere 
with orthogenesis. The causes of orthogenesis are said ‘‘to lie in the 
effects of external influeces, climate, nutrition, or the given constitu- 
tion of the organism.” 
Actual species-forming, or the breaking-up into specific units of 
the orthogenetic lines of change, depends, according to Eimer, upon 
* Jordan and Kellogg, Evolution and Animal Life (D. Appleton and Company). 
