162 Controversial Questions. 



mean of its ancestors in respect of certain characters. 

 Then we determine the curve describing the result of 

 our sowing. As a general rule, the mean of any char- 

 acter in the filial generation departs less from the normal, 

 than the character in question borne by the parent plant 

 does. According to Galton, the relation between these 

 two deviations is a constant one : the mean deviation 

 of the children amounts to about a third of that of their 

 parents. The question whether this is a universal prin- 

 ciple naturally suggests itself; the experiments which 

 I have made hitherto seem to point to the conclusion 

 that it probably is. 



8. Does this regression remain the same even when 

 selection is continued for several generations? In other 

 words, does the mean of a race never amount to more 

 than a third of the value attained by the seed bearers 

 chosen in every generation? Does the race in spite of 

 its improvement persist in this relation to its progen- 

 itors, that is to say, does it lag at every generation rela- 

 tively further behind the selected individuals w^hich pro- 

 duced it ? It seems to do ; at any rate the decision of this 

 point dominates the theory of the origin of species by 

 the natural selection of individual variations. 



9. OuETELET^s law cuablcs us to calculate from a 

 curve of variation the number of individuals that will 

 exhibit a desired degree of deviation from the mean. It 

 seems that this chance even in the case of small differ- 

 ences is a very remote one demanding as it does millions 

 of individuals. At any rate it is desirable to make such 

 calculations for as many cases as possible.-^ 



10. Artificial selection is a device for reaching a cer- 



^ See DuNCKER, Biolog. Centralbl, 1898, p. 571. For each addi- 

 tional 1000 individuals the range of variation only increases as from 

 I to 1.049. 



