THE LAW OF EVOLUTION CONTINUED. 347 



cal progression, until there is reached that complex combina- 

 tion constituting the adult. This is the history of all living 

 things whatever. Pursuing an idea which Harvey set 

 afloat, it has been shown by Wolff and Yon Baer, that dur- 

 ing its evolution each organism passes from a state of homo- 

 geneity to a state of heterogeneity. For a generation this 

 truth has been accepted by biologists.* 



§ 120. When we pass from individual forms of life to 

 life in general, and ask whether the same law is seen in the 

 enseinble of its manifestations — whether modern plants and 

 animals have more heterogeneous structures than ancient 



* It was in 1852 that I became acquainted with Yon Baer's expression of 

 this general principle. The universality of law had ever been with me a pos- 

 tulate, carrying with it a correlative belief, tacit if not avowed, in unity of 

 method throughout Nature. This statement that every plant and animal, 

 originally homogeneous becomes gradually heterogeneous, set up a process of 

 co-ordination among accumulated thoughts that were previously unorganized, 

 or but partially organized. It is true that in Social Statics (Part IV., §§ 12- 

 16), written before meeting with Von Baer's formula, the development of an 

 individual organism and the development of the social organism, are described 

 as alike consisting in advance from simplicity to complexity, and from inde- 

 pendent like parts to mutually-dependent unlike parts — a parallelism implied 

 by Milne-Edwards' doctrine of "the physiological division of labour." But 

 though admitting of extension to other super-organic phenomena, this state- 

 ment was too special to admit of extension to inorganic phenomena. The 

 great aid rendered by Von Baer's formula arose from its higher generality ; 

 since, only when organic transformations had been expressed in the most 

 general terms, was the way opened for seeing what they had in common with 

 inorganic transformations. The conviction that this process of change gone 

 through by each evolving organism, is a process gone through by all things, 

 found its first coherent statement in an essay on "Progress: its Law and 

 Cause;" which I published in the Westminster Review for April, 1857 — an 

 essay with the first half of which this chapter coincides in substance, and 

 partly in form. In that essay, however, as also in the first edition of this 

 work, I fell into the error of supposing that the transformation of the homo- 

 geneous into the heterogeneous constitutes Evolution ; whereas, as we have 

 seen, it constitutes the secondary re-distribution accompanying the primary re- 

 distribution in that Evolution which we distinguish as compound — or rather, 

 as we shall presently see, it constitutes the most conspicuous part of this sec- 

 ondary re-distribution. 



