CHAPTER XII 



IN the foregoing chapters an attempt has been made to 

 bring together the main points of the available evidence 

 with regard to the transmission of hereditary characters. 

 There are many conflicting theories with regard to the 

 various problems connected with heredity, and no doubt 

 this is in part due to the fact that general theories have 

 been based upon limited groups of phenomena, without 

 taking the evidence afforded by other groups into account. 

 Our knowledge of cell phenomena has advanced with extra- 

 ordinary rapidity in recent years, and as we have no know- 

 ledge of living matter except in the form of cells, it is 

 obvious that the evidence afforded by this branch of biology 

 must be included in all theories of evolution and heredity. 

 Unless such theories are compatible with what we know 

 happens during the processes of cell multiplication, the pro- 

 duction of the gametes, and fertilisation, they cannot be 

 true. On the other hand, no interpretation of cell pheno- 

 mena can be correct unless it harmonises with observed 

 facts with regard to the transmission of characters from 

 parents to offspring. 



When apparently contradictory groups of facts are con- 

 sidered separately by different groups of biologists, there 

 is a probability that each party will deny the facts of their 

 opponents. Something dangerously like this has occurred 

 in recent years. The Mendelians have gone very near to 

 denying any mode of hereditary transmission excepting the 

 alternative, while the biometricians have sought to explain 

 the Mendelian experiments in some way that hardly allows 

 alternative transmission as a natural phenomenon. It is 

 really ridiculous to question the observations of either party. 

 Both have provided most valuable evidence. There is no 



