40 RELATIVE STRENGTH OF NURTURE AND NATURE 



a measure of home environment, Ur Alice Lee provides me with the 

 following correlations : 



Age and acuity of vision — '037 



{i.e. the vision is slightly worse for the elder children). 



Age and home environment +'029 



{i.e. the cleanliness is slightly better with the elder children). 



Acuity of vision and home environment +'072. 



Hence the relation between goodness of vision and home environ- 

 ment for a constant age ='073, or, the relationship between home 

 environment, as measured by cleanliness of body and clothing, and 

 goodness of vision is just about one-seventh of the intensity of the 

 relationship between goodness of vision in parent and child. Nor 

 are we sure that the home environment is the source of this small 

 correlation ; for not only do the statistics indicate a marked selection 

 of the ages and the homes, but degeneracy in the parents, which is 

 usually characterised by defective vision among other factors, may be 

 the source of the want of cleanliness ; and the association of this with 

 bad vision be thus only a secondary hereditary effect. Until we know 

 far better than we do at present the closeness of correlation between 

 various physical degeneracies and the relation of these in the parent 

 to the home environment, it seems hardly possible to determine 

 whether these small correlations are really the expression of nurture, 

 or only a secondary effect of nature. What is certain is that 

 they are practically negligible compared with the direct effect of 

 nature. 



K. P. 



