INTRODUCTION 



23 



which would no doubt have gone far toward explaining evolution, was 

 overlooked for a third of a century. This was the branch of biology 

 now known as genetics, which includes heredity, variation, and related 

 subjects. 



A brilliant start was made in this field in 1866, by an Austrian monk, 

 Gregor Mendel (Fig. 14). Mendel raised peas in the monastery garden, 

 crossed a number of distinct varieties, and derived from them a simple 

 law of heredity. So occupied were biologists with Darwin's theory 

 of evolution, then in its infancy, that Mendel's writings remained un- 

 noticed until 1900, when they were rediscovered. His simple experiments 



Fig. 14. — Gregor Johann Mendel, 1822-1884. {From a pholoijraph taken about 1880. 

 Reproduced from the report of the Royal Horticultural Society Conference on Genetics, 1906. 

 By permission of the President and Council.) 



proved a tremendous stimulus to investigation, and much of the leading 

 biological work of the present century has been in the field of genetics. 

 Mendel's law of heredity has been amply verified and extended, but at 

 the same time modified. At the present time the best work in genetics 

 is being directed toward discovering the method by which hereditary 

 traits are transmitted from parent to offspring. When that is finally 

 discovered, it is not improbable that the causes of evolution will be more 

 clearly understood. 



Conclusion. — Although the foregoing account indicates the prin- 

 cipal movements in the development of zoology, and the outstanding 

 names connected with these movements, the "pure" science alone 



