NOVEMBER, 1905. OECOLOGICAL FEATURES OF EVOLUTION. 
175 
number of individuals would reach a limit. As it is evident that 
although the passive hostility might encourage the development 
of forms the environmental monotony would limit the number ; it 
is possible that we have here the explanation of the survival of 
archaic forms such as the genus Lingula among brachiopods and 
the Sphenodon among reptiles. 
In an absolutely monotonous environment there would be no 
possibility of the survival of a variety. 
In environmental diversity the hospitality of the region would 
permit the persistance of a large number of varieties this might 
be carried to such a degree that the hospitality of the region for 
a variety might be determined by one minute feature i. e. the 
animal would be highly specialized or minutely adapted. As the 
dependence of the Yucca plant on a single species of moth for 
its fertilization. 
Placing the environment of a developing form in the fore- 
ground allows of a reinterpretation of several factors of evolu- 
tion long in use. Such as the Mutation of Scott, the Definite 
Evolution of Osborn and his Homoplasy ; the Vital Principle of 
various authors. All of these assume that to some extent at 
least the animals pursue their development independent of the en- 
vironment, in spite of the environment ; that they successfully 
resist permanent environmental hostility. Williams recognized 
this in his Biological Geology, p. 35, where he says "When, how- 
ever, we are led to ask how the adjustments came about in geo- 
logical time, we have to choose an answer from these two 
possibilities, viz., either (a) slowly progressing and relatively con- 
stant evolution has taken place among organisms constantly 
struggling together and varying or (b) faunas become rapidly ad- 
justed to new conditions, attaining a biological equilibrium, and 
then maintain that equilibrium with extremely slight variation for 
great periods of time, under like conditions, but quickly and rapid- 
ly suffer specific modification whenever the environment changes, 
and the equilibrium is thus disturbed." 
Elsewhere in his book he assumes that faunas shift geogra- 
phically but says that it is "natural to suppose" that new species 
would develop in the process. This would only be possible if 
the environment changed in character as well as geographically. 
That is if a shoreline retreated by elevation of the sea bottom and 
new species developed in the process it is fair, even imperative, to 
assume that the shore line has changed somewhat in the char- 
acter of the bottom, water, temperature, etc. 
Mutations or definite evolution can only, from the very nature 
