512 HOMOGENESIS AND HETEKOGENESIS. 



grouping the new material. But such a growth can not take place to any 

 extent without a variation being encountered in the surrounding condi- 

 tions, and the instant that this occurs, differentiation ensues as its neces- 

 sary consequence. Growth under changed circumstances is then differ- 

 entiation. If the order of variation, as regards condition, is exactly the 

 Condition for same m tne case ^ two growing and differentiating combi- 

 simiiarity of nations, their career of development will be exactly alike, and 

 2nt * the* forms they will present at the same epoch of their course 

 will be the same. According as the career is short, the probabilities of 

 identity are greater, since the chances of variation, which might be en- 

 countered in the two cases, are less. But where the career is more pro- 

 tracted, and many conditions in succession must be encountered, it can 

 not happen that there will be an exact resemblance in the course of two 

 organic combinations, and therefore there never can be an absolute iden- 

 tity in the aspect of any two resulting forms. 



The general result of every development is heterogenesis. No parent 

 Development organism ever reproduces another absolutely like itself, un- 

 tendTtohete- ^ ess ** ^ e * n ^ e ^ owest developed types, in which the oppor- 

 rogenesis. tunity for change is at a minimum. Homogenesis is only ap- 

 proached as the conditions bringing on differentiation approach similari- 

 ty; it therefore sinks into a special case coming under a more general 

 law, and, indeed, speaking with exactness, we might say that in the nat- 

 ural world it never occurs, the prevalent notion which regards it as the 

 rule and heterogenesis as the exception being altogether illusory. Ev- 

 ery grade of organism, vegetable and animal, furnishes us with examples 

 of this truth. Let us look for a moment at the highest tribes ; and in 

 them reproduction never takes place except by pairs of individuals of dif- 

 ferent sexes. Eigorously, therefore, the births should also be by pairs of 

 different sexes. Moreover, if it be necessary in these general and super- 

 ficial considerations, let us direct our attention to the special case of man. 

 The infant necessarily differs from one of its parents in sex, and from 

 both in size, weight, endowments, and' physical attributes. It is like 

 neither of them. The popular notion may suggest that a closer resem- 

 blance will be reached, perhaps, after the lapse of thirty or forty years, 

 when a nearer approach to the form of one of the parents may be offered 

 with elements incorporated from the lineaments of the other ; but even 

 m this case a rigorous examination compels us to admit that like has not 

 produced like. 



Eeflecting on this popular illustration more profoundly, we discern 

 Cycles of pro- wherein the error consists. Instead of comparing cycles of 

 C ared and 00 " P rocess we ^ ave ^ een blundering with isolated forms, which 

 individual arise at different epochs therein. Without going into tedi- 

 ous details, man presents, as regards the most important of 



