18 PRINCIPLES OF ANIMAL BIOLOGY 



theory — natural selection — to account for it, so plausible that acceptance 

 of the fact of evolution was rendered easy. Within a few years of the 

 publication of Darwin's "Origin of Species" in 1859, the supporters of the 

 evolution idea far outnumbered its opponents in intellectual circles. 

 Naturalists everywhere were busy finding examples of apparent evolution 

 and striving to fit the observed facts into the natural selection theory. 

 The whole course of development of biology was modified by this prev- 

 alence of evolutionary speculation during the two or three decades after 

 1859. 



Not all discussions of evolution were wholly speculative; some were 

 founded on detailed facts which were gained by hard labor. An example 

 is the expansion of work in comparative morphology in Germany. This 

 science became distinctly evolutionary; the comparisons were made with 

 an eye to kinship and became some of the most important of the evidences 

 of evolution. Embryology, too, profited by the idea of kinship of animal 

 forms and in turn furnished much of the evidence on which the evolution 

 theory is based. Only among the French, of the great intellectual 

 peoples, was the acceptance of the evolution doctrine long delayed; and 

 when the idea finally triumphed there, it was rather in the form proposed 

 by their countryman Lamarck (as a consequence of use and disuse) than 

 in the Darwinian form (as guided by natural selection). 



Genetics. — In one respect in particular did enthusiasm for the 

 evolution theory overreach itself. Since evolution can consist only of 

 hereditary variations, it would be supposed that any information regard- 

 ing the phenomena of heredity would be promptly seized upon as of 

 importance to evolution. Darwin himself did strive to learn from 

 practical breeders and others what was known of these phenomena. 

 His feeling of their importance was not shared sufficiently by biologists 

 in general, so that when in 186G Gregor Mendel (Fig. 14), an Austrian 

 monk, published some experiments dealing with inheritance in garden 

 peas, they attracted no attention. Mendel's work lay unnoticed until 

 1900. By that time the ardor of the natural selectionists had cooled 

 enough that the futility of attempting to discover the course of evolution 

 by speculation alone was duly recognized. Realizing that in a knowledge 

 of heredity lay the best hope of explaining evolution, various biologists 

 had resumed the study of inheritance by means of experiments. Plants, 

 being simplest, yielded the first results, and in 1900 three European 

 botanists, working independently, publislunl at about the same time 

 accounts of their crosses, from which they derived the same conclusion as 

 Mendel had derived before them. Fortunately they also discovered 

 Mendel's old paper. These experiments were capable of being explained 

 in so simple a manner that a great impetus was given to the experim(;ntal 

 study of heredity. Hundreds of plants and animals have been shown to 



