THE EVOLUTION OF LIVING BEINGS. 77 



favour to homozygotes, as happens in the case of habitual 

 self fertilisers. 



This agrees fully with Baurs results, calculated on 

 the basis of promiscuous mating of white and black 

 mice, about which he says: 



,,Ueberlassen wir nun eine Population vain dieser Zu- 

 ,,sammensetzung sich zur weiteren panmiktischen Ver- 

 ,,mehrung, so werden alle folgenden Generationen das 

 ,,gleiche Zahlenverhaltniss zwischen den weissen (aa) 

 ,,und den beiden sorten (AA und Aa) von schwarzen 

 ,,Tieren aufweisen." 



These calculations consequently lead to the result: 



Self fertilisation after a cross leads to a considerable 

 proportional increase of the homozygotes in subsequent 

 generations, random mating has no such effect : the pro- 

 portion of homozygotes to heterozygotes remains the same 

 in successive generations, 



Now all such calculations suffer from the impossible 

 supposition that all individuals born, reach maturity, 

 form an equal number of gametes, and that all these 

 gametes mate and form viable zygotes, by which kind 

 of calculation as is well known a human couple, 

 in the possession of one cock and six hens, can look for- 

 ward not only to a prosperous, but even to a wealthy life. 



Unfortunately, the ideal conditions on which such 

 calculations are based are never realised, so that the 

 calculated proportion of homozygotes to heterozygo- 

 tes is valueless, also because strict selffertilisation ne- 

 ver persists in nature, even not in such ,,typical" self- 

 fertilizers as wheat. 



So NILSSON-EHLE showed that Pudelweizen can be 



