260 ORIGIN OF SPECIES 



in an abrupt or sudden manner. Nor should it be forgotten, 

 when we look to the special parts of allied species, instead of 

 to distinct species, that numerous and wonderfully fine grada- 

 tions can be traced, connecting together widely different 

 structures. 



Many large groups of facts are intelligible only on the 

 principle that species have been evolved by very small steps. 

 For instance, the fact that the species included in the larger 

 genera are more closely related to each other, and present a 

 greater number of varieties than do the species in the smaller 

 genera. The former are also grouped in little clusters, like 

 varieties round species ; and they present other analogies with 

 varieties, as was shown in our second chapter. On this same 

 principle we can understand how it is that specific characters 

 are more variable than generic characters ; and how the parts 

 which are developed in an extraordinary degree or manner 

 are more variable than other parts of the same species. 

 Many analogous facts, all pointing in the same direction, 

 could be added. 



Although very many species have almost certainly been 

 produced by steps not greater than those separating fine vari- 

 eties ; yet it may be maintained that some have been devel- 

 oped in a different and abrupt manner. Such an admission, 

 however, ought not to be made without strong evidence being 

 assigned. The vague and in some respects false analogies, 

 as they have been shown to be by Mr. Chauncey Wright, 

 which have been advanced in favour of this view, such as the 

 sudden crystallisation of inorganic substances, or the falling 

 of a facetted spheroid from one facet to another, hardly de- 

 serve consideration. One class of facts, however, namely, the 

 sudden appearance of new and distinct forms of life in our geo- 

 logical formations supports at first sight the belief in abrupt 

 development. But the value of this evidence depends entirely 

 on the perfection of the geological record, in relation to 

 periods remote in the history of the world. If the record is 

 as fragmentary as many geologists strenuously assert, there 

 is nothing strange in new forms appearing as if suddenly 

 developed. 



Unless we admit transformations as prodigious as those 

 advocated by Mr. Mivart, such as the sudden development of 



