n8 BIOMETRY 



and show no regression towards the type of the general 

 population to which the group belongs. 



If we were to carry on this conception to the case of 

 bisexual inheritance, we should find that the different 

 pure lines would become crossed and confused together 

 in a way which would be very difficult to disentangle. 

 There is no reason to doubt that statistical treatment 

 of such a population would yield similar results to 

 those actually obtained by biometricians from the 

 data at their disposal ; and we may notice that a for- 

 tuitous mixture of a considerable number of pure 

 lines, having slightly different types, would admirably 

 fulfil the conditions we have seen to be necessary in 

 the case of material, to which methods based upon 

 the theory of chance are to be applied. The phe- 

 nomena which follow upon the crossing together of 

 two or more pure lines have been found, in the majority 

 of cases so far studied, to conform to those laws of 

 heredity associated with the name of Mendel which 

 are explained in Chapter VII. This being the case, 

 there appears to be every probability that the theory 

 of pure lines, in combination with the method of in- 

 heritance referred to, may adequately serve to describe 

 those phenomena to account for which the law of 

 ancestral inheritance was called into existence. 



The conclusions to which Professor Johannsen's 

 experiments lead him may be summed up as follows : 

 Individuals which differ (in size, for example) from 

 the mean of a population give rise to offspring which 

 differ from that mean value in the same direction 

 but to a smaller extent. Selection, therefore, will 



