CONCLUSIONS 157 



It would seem a good principle to encourage the study of 

 " scientific heresies." There is always the danger that a reader 

 might be seduced by one of these heresies but the danger is 

 neither as great nor as serious as the danger of having scientists 

 brought up in a type of mental strait-jacket or of taking them so 

 quickly through a subject that they have no time to analyse and 

 digest the material they have " studied." A careful perusal of the 

 heresies will also indicate the facts in favour of the currently 

 accepted doctrines, and if the evidence against a theory is over- 

 whelming and if there is no other satisfactory theory to take its 

 place we shall just have to say that we do not yet know the answer. 



There is a theory which states that many living animals can be 

 observed over the course of time to undergo changes so that new 

 species are formed. This can be called the " Special Theory of 

 Evolution " and can be demonstrated in certain cases by experi- 

 ments. On the other hand there is the theory that all the living 

 forms in the world have arisen from a single source which itself 

 came from an inorganic form. This theory can be called the 

 " General Theory of Evolution " and the evidence that supports 

 it is not sufficiently strong to allow us to consider it as anything 

 more than a working hypothesis. It is not clear whether the changes 

 that bring about speciation are of the same nature as those that 

 brought about the development of new phyla. The answer will 

 be found by future experimental work and not by dogmatic 

 assertions that the General Theory of Evolution must be correct 

 because there is nothing else that will satisfactorily take its place. 



