242 NOTES AND COMMENTS [ocroBER 
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, eg. 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. 
NATURALISTS 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 
