530 Colonel K. Meinertzhagen on [Ibis, 



portion, and that a very small one, can survive to 

 produce offspring. The nature of the surviving portion 

 is not determined by chance alone. No two individuals 

 of a species are exactly alike, and among the variations 

 which occur some enable their possessors to cope more 

 successfully with the competitive conditions under 

 which they exist. In comparison with their less 

 favoured brethren they have a better chance of sur- 

 viving and consequently of leaving offspring. Off- 

 spring tend to resemble their parents more than other 

 members of the species, and favourable variations are 

 transmitted. 

 In opposition to the Darwinian Theory is the Mutational 

 Theory, which believes that new varieties suddenly arise 

 from older ones by sharp sudden steps or mutations, and not 

 by any process involving the gradual accumulation of minute 

 differences. Such mutations turn up suddenly complete 

 in themselves and are therefore " sports," their origin or 

 meaning being unknown. Where such differences are due 

 to a change in the gamete, they are heritable, are termed 

 mutations, and are good species. Where such variations are 

 not heritable, they are termed fluctuations and can never 

 become permanent. Hybrids are, of course, mongrels, and 

 no amount of selection, artificial or natural, can fix them as 

 species. 



Mutation is therefore regarded as the basis of all evolution, 

 though it is conceded that th(^ continued existence of a 

 mutation is subject to natural selection. 



Such is the theory based on MendeFs experiments and on 

 the work of his many later disciples. 



An examination of the experiments on which the Men- 

 delian theories are based shows that they have been almost 

 exclusively undertaken on plants and domesticated animals . 

 and under artificial conditions. In fact, they could not have 

 been undertaken in any other medium. I believe that selec- 

 tion by man, and the perpetuation of sports or mutations as 

 permanent varieties, whose differences are heritable, is a state 

 which occurs but rarely in nature, and most of the deductions 



