Publisher's Synopsis
Excerpt from Bursa Bursa-Pastoris and Bursa Heegeri Biotypes and Hybrids
Darwin recognized in the facts of variation a key to the riddle presented by the multiformity and many obvious interrelations of all living things. Since the appearance of the Origin of Species the observation and discus sion of variations have assumed a dominant place in biology, and a serious con?ict has recently developed regarding the interpretation of the observed facts. It is now generally recognized that this con?ict can be brought to a termination only through the application of experimental methods. Inspection alone can not decide the question as to how an observed varia tion originated and what bearing it may have on the future of the race in which it occurs. Studies in the museum and in the field only discover the fact, and to some extent the range, of variation occurring under a more or less limited and inadequately known range of conditions, and can not cer tainly determine its cause or causes neither can these means supply more than a suggestion based upon insecure inference as to the hereditary nature of any variation. The causes of variation can be determined only by subjecting equivalent material to different controlled conditions, and their hereditary relations can be learned only through the conduct of pedigree cultures.
We already know, as a result of experimental work in these directions, that variations are of fundamentally different types, having different causes and obeying different laws of development and heredity. A knowledge of these facts impresses an important principle, namely, that the range of applicability of any conclusion reached by the investigation of one class of material or one characteristic can be determined only by similar experiments with other material and other characteristics.
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