242 NOTES AND COMMENTS [october 



desire to see it at work is to determine the relative amounts of the 

 selective and non-selective parts of the death-rate for individuals 

 living under the like environment. If, therefore, individuals living 

 under much the same conditions are dealt with, the determination of 

 the selective and non - selective death - rates is a measure of the 

 quantitative amount of natural selection." 



One method of dealing with the problem has been followed by 

 Professor Weldon, who selected a certain structural part (in crabs), 

 and sought to determine whether the death-rate is a function of the 

 dimensions of this part. Another method has been followed by the 

 authors. " We do not attempt to select any organ whatever, but 

 select individuals having any general resemblance in their constitution, 

 or in the whole complex of organs and characters, and correlate their 

 fitness for surviving. Now relations or members of the same family 

 are precisely such individuals. If there were no selective death-rate, 

 there would be no correlation between the ages of death of, say, 

 brothers. If there were no non-selective death-rate, we ought to find 

 that the correlation between ages of death of brothers takes the value 

 determined for the coefficient of heredity^ in brothers, c.<j. the '4- of 

 stature, fore-arm, cephalic index, eye-colour, etc. Actually we find it 

 to be something sensibly less than *4. Our investigation shows that, 

 in round numbers, about 80 per cent of the death-rate is selective in 

 the case of mankind. To that extent natural selection is actually 

 at work." 



The authors close the abstract of their interesting preliminary 

 paper with an appeal for biological experiment. " Various types of 

 life ought to be submitted to ordeals of a kind like to those which 

 occur in nature, and the correlation between the powers of resistance 

 to these ordeals existing in members of the same family or brood 

 determined. We shall thus be able to ascertain under a variety of 

 circumstances the relative proportions of the selective and non- 

 selective death-rates. . . . One may venture to express the hope that 

 in a comparatively few years, if enough workers can be found for 

 the experimental side of the subject, we shall no longer hear natural 

 selection spoken of as hypothetical, but rather its quantitative measure 

 given for various organisms under divers environments." 



A Verbose Vitalist. 



Natukalists of an earlier day would probably be surprised — if not 

 shocked — at some of the contents of modern biological journals. We 

 refer to the now frequent occurrence of pages thickly strewn with 

 equations and mathematical symbols, of others bristling with "categories" 

 and " principles," of others where the author seems at first to be living in 



