124 
Reviews 
REVIEWS 
GENETICS AND EVOLUTION 
Hagedoorn, A. L. and Hagedoorn, A. C. The Relative Value 
of the Processes Causing Evolution. Pp. 294. Martinus Nijhoff. 
The Hague, 1921. Price 9 guilders. 
The authors of this very interesting book, on the basis of a long personal 
experience of genetic research, a wide acquaintance with the literature, and— 
not least important for their task—an evidently extensive knowledge of the 
world, of the different nations, races and classes of man, and of the breeds of 
domestic animals and plants, discuss afresh the still unsettled question of the 
factors of organic evolution. The following review does not profess to be critical. 
It aims simply to give the ordinary botanist some idea of what the book 
contains. 
The authors call attention to the wide divergences of opinion still existing 
as to the factors of evolution, in spite of the enormous development of genetic 
research during the last 20 years, and to the reluctance of geneticists to make 
any attempt to correlate the facts so far obtained. This reluctance is not quite 
universal. The authors pay tribute to Bateson’s subordination of the different 
specialised genetic investigations to the main problems of evolution 1 . “ The first 
author,” they say, “after Darwin who approached genetics in this spirit was 
Bateson.” And Gates, in the pages of this Journal 2 , and elsewhere, has recently 
made similar attempts. It may be urged of course that we still do not know 
enough of the facts to theorise safely about evolution and that we must await 
the results of further research before attempting to do so. It is clear in any 
case that general theorising about evolution must still be provisional. It can 
only be a question of reviewing, from time to time, the knowledge accumulated, 
and of endeavouring to see where we stand. This the ordinary biologist is unable 
to do for himself owing to the extremely specialised work of the modern geneti¬ 
cist, and the complicated and unfamiliar language in which it is expressed. 
Meanwhile it is evident that the subject is still liable to the over-emphasis 
of single factors on the part of individual theorists. “ There is one point common 
to all the theories of evolution, excepting Darwin’s, and that is that each theorist 
has always over-emphasised one point, one single link in the chain of processes 
which goes to the making of species, and has brought out this point as ‘ the ’ 
cause of evolution. Just as Lamarck gave all his attention to adaptation 
\i.e. direct adjustment to environment] and led himself to believe that adapta¬ 
tion is the cause of numerous processes with which we now believe it to be 
1 The Problems of Genetics, Yale University Press, 1913; Presidential Address to 
the British Association, London, 1914. 
2 “Mutations and Evolution,” New Phytologist, 19 , 1920. (Reprint, No. 12, 1921.) 
