August 25, 1911] 



SCIENCE 



241 



as a novel. It deals with the new science of 

 genetics, " the experimental study of heredity 

 and variation in animals and plants," and 

 contains the clearest and best account of its 

 rise and present condition that has yet been 

 published in any language. It lacks the ency- 

 clopedic completeness and the bibliographic 

 features of the work of Bateson and Przi- 

 bram, and will of course need to be supple- 

 mented by them in the hands of the advanced 

 student, but for the beginner or the general 

 reader who wants within moderate compass a 

 sane and well-balanced account of what has 

 been accomplished in this field, the book is 

 almost ideal. 



It does not pretend to give an account of 

 all the work done in this field, but of only so 

 much of it as will serve adequately to illus- 

 trate the principles involved. The author 

 writes in his preface: 



In choosing typical examples to illustrate the 

 growth of our ideas it was natural that I should 

 give the preference to those with which I was 

 most familiar. For this reason the book is in 

 some measure a record of the work accomplished 

 by the Cambridge School of Genetics, and it is not 

 unfair to say that under the leadership of William 

 Bateson the contributions of this school have been 

 second to none. But it should not be forgotten 

 that workers in other European countries, and 

 especially in America, have amassed a large and 

 valuable body of evidence with which it is impos- 

 sible to deal in a small volume of this scope. 



The illustrative material, however, has been 

 remarkably well selected, and the wide range 

 of questions upon which it bears speaks elo- 

 quently of the industry of the workers in 

 " the Cambridge School " and their clear 

 vision of what are the vital problems in gen- 

 etics. Needless to say this book is an exposi- 

 tion of orthodox " Mendelism." Gametes are 

 treated as beyond suspicion " pure," and unit- 

 characters are regarded as immutable. Varia- 

 tion is supposed to occur only by loss of fac- 

 tors, or by the interpolation of new, " modify- 

 ing," " intensifying " or " inhibiting " factors, 

 but never by a direct change in the factors 

 that before existed. There are Mendelians 

 who are heterodox or at least have inner ques- 

 tionings about some of these assumptions, and 



are likely to challenge them in the next ten 

 years as they have in the last ten. But the 

 author has wisely omitted controversial points 

 from a general and introductory account of 

 his subject. His account shows that a really 

 great advance has been made in the study of 

 evolution since the rediscovery of Mendel's 

 law and the readoption of the experimental 

 method of studying variation and heredity. 



The book opens with a brief statement of 

 " the problem," of the source of new indi- 

 viduals in the gametes, and their part in the 

 life-cycle. This is followed by a likewise brief 

 but well-proportioned historical account of 

 Mendel's work and of that of his predecessors, 

 as well as of the Darwinian period following 

 Mendel's time. The essential points in Men- 

 del's work are shown to be the existence of 

 unit-characters and their segregation, domi- 

 nance being an incidental matter. The rest 

 of the book is concerned largely with the de- 

 velopment of Mendelian ideas since the redis- 

 covery of Mendel's law in 1900. 



The " presence and absence " theory is built 

 up with great skill and clearness from an 

 analysis of the inheritance of comb-form in 

 fowls. This theory has all but replaced the 

 earlier idea of Mendel, that the recessive char- 

 acter is something no less real than the dom- 

 inant one which obscures it in crosses. The 

 presence and absence theory asserts that the 

 recessive character has no objective existence 

 except as the absence of the dominant one. 

 Punnett, however, like most other Mendelians, 

 retains Mendel's original terminology, even 

 though it has lost its original significance. 

 The small letter used to designate a recessive 

 character means, on the presence and absence 

 theory, only that there is nothing there, and it 

 would seem might as well be dropped in the 

 interest of simplicity. But if it can yet be 

 shown that there are cases in which the re- 

 cessive character is a reality, as Mendel 

 thought, and not a mere negation, the old 

 terminology may reacquire significance and 

 utility. 



A chapter devoted to the " interaction of 

 factors " shows how the presence of one unit- 

 character may affect the manifestation of an- 



