PREFACE 



THERE is a good deal that is new a little of which I hope 

 will be found true in this volume. It follows somewhat 

 on the lines of my former work, The Present Evolution of Man, 

 from which I have borrowed occasionally, especially in 

 Chapter XI., and in the section devoted to Mind. 



The evidence bearing on Heredity afforded by disease has 

 hitherto been scarcely touched. It is utilized largely in the 

 present work. I cannot help thinking that most students of 

 Heredity are not aware of the value of this evidence from 

 disease. I believe that if it had been considered in conjunc- 

 tion with the facts of specific adaptation to the environment 

 a good deal of controversy concerning the transmission of 

 acquirements and the origin of variations would not have 

 occurred, or at any rate would not have lasted as long as it 

 has done. So far as I am able to judge, it establishes 

 conclusively the facts (1) that parental acquirements are 

 never transmitted to offspring, and (2) that variations are 

 rarely caused by the direct action of the environment on 

 the germ-cells so rarely that racial change is never due, 

 directly or indirectly, to this cause. The great mass of 

 variations have another origin which I have endeavoured 

 to elucidate. 



The function of bi-parental reproduction appears to me 

 manifest. It is very important, but it has nothing to do 

 with the causation of progressive variations. 



In the fifth chapter I have sought to re-establish on a firm 

 basis the doctrine that the development of the individual is 

 a blurred recapitulation of the life-history of the race. The 

 doctrine of recapitulation has been controverted of late ; but 

 in the whole range of biology there is nothing that is more 

 certainly true. It follows logically and necessarily from the 

 known fact that the child recapitulates the developmental 

 footsteps of the parent. Unless it were true there could be 

 no development of the individual and no evolution of the race. 

 This fifth chapter is the crux of the whole work. If the 

 scientific reader finds its reasoning correct and its conclusions 

 valid, he will probably not raise much objection to the rest of 

 the book. 



I have addressed the volume mainly to medical men. The 



