1216 ; Growth, its Conditions and Variations. [December, 
inant form of animals was replaced by another form of different 
type which had been slowly growing up beneath it, or more 
probably had migrated from another locality into one whose food 
animals were helpless before its assault. But there is another 
case of extreme importance, that of the apparently sudden re- 
placement of one species by another of the same genus or family, 
usually of superior organization, with no trace of steps of suc- 
cession from the one form to the other. This absence of link- 
forms between closely related species is one of the most marked 
characteristics of paleontological evidence, and seems to strongly 
hint at specific succession by leaps instead of by minute steps. 
Yet the question of food supply yields one argument in favor of 
the latter which may be here given. 
A replacement of one species by another indicates that the 
second is in some way better adapted to the existing conditions 
of nature, or to new ones which have arisen. In other words, it 
is suited to obtain more food with equal exertion, or equal food 
with less exertion. But the competition which arises is stronger 
and closer between the offspring and the parental form than be- 
tween diverse forms. The two related forms are adapted to the 
same kinds of food, and are closely similar in weapons and hab- 
its. Hence of all forms of animal life the one which is put mot 
at disadvantage by the food taking ability of a new form iS al 
parental form. Other tribes of different organization and habits 
come less into competition with it, or at less disadvantage. If 
adapted to an entirely different food there is no competition. 
Thus two important results are likely to spring from the evolu- 
tion of a new animal form, specially well adapted to the ai 
conditions of surrounding nature, or possessed of a variety 
weapon or habit of assault to which the food has gained n de- 
fensive adaptation. One of these results must be the rapid oe 
appearance of the parental form, which will be starved out © 
existence. And if there be several successive link-forms, 
must rapidly yield to its successor. Thus if a considerable 
rapid change of natural conditions necessitates a similar rap“ 
Succession of specific variations in some animal tribe, not only © 
original form would vanish, but the link forms would quickly m 
appear. The new dominant form would tread down its steps ef 
advancement, and the intermediate forms, having a comparati fa 
short term of existence, and giving rise to comparatively ay 
