PREFACE 
From ancient times heredity has been looked upon 
as one of the central problems of biological philoso- 
phy. It is true that this interest was largely specu- 
lative rather than empirical. But since Mendel’s 
discovery of the fundamental law of heredity in 
1865, or rather since its re-discovery in 1900, a curious 
situation has begun to develop. The students of 
heredity calling themselves geneticists have begun 
to draw away from the traditional fields of zoology 
and botany, and have concentrated their attention 
on the study of Mendel’s principles and their later 
developments. The results of these investigators 
appear largely in special journals. Their terminology 
is often regarded by other zoologists as something 
barbarous,—outside the ordinary routine of their pro- 
fession. The tendency is to regard genetics as a sub- 
ject for specialists instead of an all-important theme of 
zoology and botany. No doubt this is but a passing 
phase; for biologists can little afford to hand over to 
a special group of investigators a part of their field 
that is and always will be of vital import. It would 
be as unfortunate for all biologists to remain ignorant 
of the modern advances in the study of heredity as 
it would be for the geneticists to remain unconcerned 
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