EVOLUTION AND MENDELISM 



By R. BROOM, D.Sc. 



The appearance of Darwin's Origin of Species fifty-six years 

 ago is generally admitted to have been the most important event 

 in the history of biology. Though others before him had be- 

 lieved in the evolution of living forms, it was not till Darwin had 

 brought together and arranged his wondrous wealth of facts 

 that the scientific world was convinced that whatever the 

 cause or causes of evolution there was no longer any doubt 

 as to the fact. Wallace and Darwin further advanced the 

 very plausible theory that the natural selection of the varieties 

 best fitted to survive in the struggle for existence was the chief 

 factor in the evolution. 



Many, perhaps the majority of biologists, accepted this 

 theory of Wallace and Darwin as giving a satisfactory explana- 

 tion : others, while accepting the truth of evolution, felt that 

 though natural selection had undoubtedly played a part, there 

 must have been some other agency. Of these latter Cope was 

 one of the most prominent, and in his book The Origin of the 

 Fittest he endeavours to get at the causes of the fitness that 

 is selected. 



In the last thirty years there has been very little advance 

 made in our knowledge of the causes of evolution, but our 

 knowledge of the facts of biology has increased enormously. 



The embryological history of most of the principal living 

 types is now fairly well known ; while palaeontology can now 

 give a moderately satisfactory view of the types of animals, 

 and to a less degree of the plants, which flourished in the 

 various geological epochs. 



New fields have been opened up by experimental embry- 

 ology, and the minute study of the animal cell and the changes 

 that take place during fertilisation and cell division has greatly 

 added to our knowledge. 



Since the beginning of the twentieth century, perhaps the 

 most important biological work that has been done has been 



