THE LAW OF EVOLUTION CONTINUED. 375 



changes from order towards disorder, they cause changes 

 from definite arrangements to indefinite arrangements. 



Thus, then, is that increase of heterogeneity which con- 

 stitutes Evolution, distinguished from that increase of 

 heterogeneity which does not do so. Though in disease 

 and death, individual or social, the earliest modifications 

 are additions to the pre-existing heterogeneity, they are 

 not additions to the pre-existing definiteness. They begin 

 from the very outset to destroy this definiteness; and 

 gradually produce a heterogeneity that is indeterminate 

 instead of determinate. As a city, already multiform in its 

 variously-arranged structures of various architecture, may 

 be made more multiform by an earthquake, which leaves 

 part of it standing and overthrows other parts in diiferent 

 ways and degrees, but is at the same time reduced from 

 orderly arrangement to disorderly arrangement; so may 

 organized bodies be made for a time more multiform by 

 changes which are nevertheless disorganizing changes. 

 And in the one case as in another, it is the absence of 

 definiteness which distinguishes the multiformity of regres- 

 sion from the multiformity of progression. 



If advance from the indefinite to the definite is an 

 essential characteristic of Evolution, we shall of course find 

 it everywhere displayed; as in the last chapter we found 

 the advance from the homogeneous to the heterogeneous. 

 With a view of seeing whether it is so, let us now re-con- 

 sider the same several classes of facts. 



130. Beginning, as before, with a hypothetical illus- 

 tration, we have to note that each step in the evolution of 

 the Solar System, supposing it to have originated from dif- 

 fused matter, was an advance towards more definite struc- 

 ture. At first irregular in shape and with indistinct margin, 

 the attenuated substance, as it concentrated and began to ro- 

 tate, must have assumed the form of an oblate spheroid, 

 which, with every increase of density, became more specific 



