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BOOK Y. INORGANIC EVOLUTION. 

 CHAP. XIX. WHAT EVOLUTION MEANS : ORGANIC EVOLUTION. 



IN the previous chapters I have endeavoured to correlate all the facts 

 which have been obtained during the last, let us say, thirty years, in 

 relation to the sun, with more recent facts that have been gathered 

 with regard to the stars. In this we were, by hypothesis, watching 

 the effects of dissociation as the temperature rose higher and higher ; 

 we have found that the dissociation hypothesis, the view, namely, that 

 at high temperatures the chemical units with which we work at low 

 temperatures are broken up into smaller masses, explains the spectral 

 phenomena observed not only in our laboratories but in the sun and 

 stars. 



I have also shown that in the opinion of many investigators suck a 

 dissociation is necessary to explain the phenomena observed in physi- 

 cal inquiries other than those which directly concern us here. 



In these concluding chapters I propose to change the point of view, 

 to consider the phenomena no longer from the point of view of dis- 

 sociation but from that of evolution. 



What is evolution 1 To answer this question I can refer to 

 another line of work in which the word is frequently used and 

 thoroughly understood. It is important that I should do this for 

 another reason, which will be gathered later. That line of work has 

 to do, not with inanimate forms, like the chemical elements and the 

 stars, but with living things, with so-called organisms. Most of my 

 readers know that what we now recognise as one of the greatest 

 triumphs of the century just ending was the determination of the truth 

 of a so-called " organic evolution " in which we have, I suppose, the 

 most profound revolution in modern thought which the world has 

 seen. 



That evolution tells us that each kind of plant and animal was not 

 specially created, but that successive changes of form were brought 

 about by natural causes, and that the march of these forms was from 

 the more simple to the more complex. Organic evolution, in fact, 

 may be defined as the production of new organic forms from others 

 more or less unlike themselves ; so that all the present plants and 



