92 Heredity and Variation in Modem Lights 



If, then, progress was to be made in Genetics, work of a different 

 kind was required. To learn the laws of Heredity and Variation 

 there is no other way than that which Darwin himself followed, the 

 direct examination of the phenomena. A beginning could be made 

 by collecting fortuitous observations of this class, which have often 

 throMii a suggestive light, but such evidence can be at best but 

 superficial and some more penetrating instrument of research is 

 required. Tliis can only be provided by actual experiments in 

 breeding. 



The truth of these general considerations was becoming gi-adually 

 clear to many of us when in 1900 Mendel's work was rediscovered. 

 Segregation, a phenomenon of the utmost novelty, was thus revealed. 

 From that moment not only in the problem of th.e origin of species, 

 but in all the great problems of biology a new era began. So un- 

 expected was the discovery that many naturalists were convinced it 

 was untrue, and at once proclaimed Mendel's conclusions as either 

 altogether mistaken, or if true, of very limited application. Many 

 fantastic notions about the workings of Heredity had been asserted 

 as general principles before : this was probably only another fancy of 

 the same class. 



Nevertheless those who had a preliminary acquaintance with the 

 facts of Variation were not wholly unprepared for some such revela- 

 tion. The essential deduction from the discovery of segregation was 

 that the characters of living things are dependent on the presence of 

 definite elements or factors, which are treated as units in the pro- 

 cesses of Heredity. These factors can thus be recombined in various 

 ways. They act sometimes separately, and sometimes they interact 

 in conjunction with each other, producing their various effects. All 

 this indicates a definiteness and specific order in heredity, and there- 

 fore in variation. This order cannot by the nature of the case be 

 dependent on Natural Selection for its existence, but must be a con- 

 sequence of the fundamental chemical and physical nature of living 

 things. The study of Variation had from the first shown that an 

 orderliness of this kind was present. The bodies and the properties 

 of living things are cosmic, not chaotic. No matter how low in the 

 scale we go, never do we find the slightest hint of a diminution in 

 that all-pervading orderliness, nor can we conceive an organism 

 existing for a moment in any other state. Moreover not only does 

 this order prevail in normal forms, but again and again it is to be 

 seen in newly-sprung varieties, Avhich by general consent cannot have 

 been subjected to a prolonged Selection. The discovery of Mendelian 

 elements admirably coincided with and at once gave a rationale of 

 these facts. Genetic Variation is then primarily the consequence of 

 additions to, or omissions from, the stock of elements which the 



