188 THE TREND OF THE RACE 
we must bear in mind that their better environment is to a large 
extent the result of their belonging to hereditary stocks at least 
a little above the general average of humanity. If the birth rates 
of the classes that achieve success by virtue of their inherent 
superiority were as high or nearly as high as it is among their 
less favored brethren the general level of ability would doubtless 
be raised through natural selection. Unfortunately under our 
present social conditions natural selection and reproductive 
selection frequently work in opposite directions, and the evidence 
points to the conclusion that the influence of the latter is gener- 
ally the more potent. 
For a number of years Professor Karl Pearson and several of 
his associates have been endeavoring to demonstrate by statistical 
methods that natural selection is actually at work among human 
beings and to obtain a measure of the intensity of its action. 
From data on the general health of professional classes which were 
exposed to much the same environmental influences, Pearson 
found a parent-offspring correlation of .3824 which is indicative 
of a fair amount of hereditary resemblance. Longevity was found 
by Beeton and Pearson to run in families as has long been believed 
and as in fact common observation seems to show. In selected 
groups such as the British Landed Gentry and the Peerage where 
environmental differences play a relatively small réle, a marked 
correlation was found between the length of life of father and son 
and also between the length of life of brothers. Great length 
of life was also found to be correlated with increased fertility. 
It is, of course, obvious that up to the end of the reproductive 
period, the longer people live the more children they may be 
expected to have. But the fact that the longer women live after 
their reproductive period the more children they are likely to have 
in this period indicates that increased fertility and longevity are 
both the result of a high degree of vitality. ‘‘Of two women who 
both lived beyond 50 years, the longer lived is likely to have had 
before 50 the larger family.”” (Beeton, Yule and Pearson.) 
Similar results were obtained by Powys from data obtained 
in New South Wales. Fecundity was found to increase in women 
