vi PREFACE 



and not confuse fact with speculation, I have tried to 

 avoid purely speculative questions in the body of the 

 book, and have devoted a few pages to one of the most 

 interesting of these in an appendix, together with a 

 historical summary of Theories of Heredity. There 

 are many, of course, who will regard parts of the 

 chapters dealing with Mendelism as consisting largely 

 of speculation ; I can only reply that I regard the 

 facts referred to as established, and the theoretical 

 deductions from them as the only ones that have 

 yet been offered which can fit them adequately. 



No attempt has been made to quote authorities 

 for every statement, but a list of books and papers is 

 given in which a further account will be found of the 

 subjects treated. The numbers in square brackets [ ] 

 in the text refer to this list. I have also followed 

 the example set by Mr Lock in providing a glossary 

 of unfamiliar terms of which the use has been 

 unavoidable. 



For the chapter on Statistical Study of Inherit- 

 ance my chief sources of information have been 

 Prof. Pearson's Grammar of Science and his numerous 

 papers on the subject published by the Royal Society 

 and in Biometrika. I have tried to summarise in 

 words the results of his work, and of that of other 

 workers on similar lines, and if the inadequacy of my 

 mathematical knowledge has led me into any serious 

 errors in the attempt, I owe them my apologies. 



