280 
PROFESSOR KARL PEARSON AND MISS ALICE LEE, 
fertility of marriages, which were formed with husband and wife between 20 and 
28"' say, and which have lasted till the wife is over 50. But these conditions must 
be true in two successive generations, and, had we adopted them, we may safely say 
that without immense labour it would have been impossible to collect even a 
thousand cases. From the wBole of the peerage, the baronetage, the landed gentry, 
a variety of family histories, of private pedigrees, and a collection of data formed of 
families at first hand, it was not possible to extract more than about 4000 cases for 
the inheritance of fertility in the female line, when the limitations were far less 
stringent, being applied only to one generation, and consisting in our taking marriages 
entered into at any time of life for either husband or wife, and lasting till the death 
of one member or for at least fifteen years. Even in this case the pedigree of the 
wife had to be sought for from one record to another and often in vain. It is the 
male pedigree with which the recorder in nearly all cases occupies himself. 
Only those who have attempted the labour of extracting, as has been done in this 
case, some 16,000 separate returns, will fully grasp the difficulty of making the 
limitations of selection more and more complex ; the quantity to be obtained becomes 
dangerously small and the labour immensely increases. Even could with time and 
patience a sufficient selection of ideal cases have been made, it does not follow that 
the result would be satisfactory ; for, we should have made a narrow selection, and 
this very fact might indicate that possibly we have been selecting one grade or class 
of fertility. It is possible that the less fertile are the weaker, and so more liable 
to die early ; or again it may be the more fertile wmmen who are subjected to the 
more frequent risk of childbed, and thus are less likely to appear in the selection of 
long marriages. Even greater or less risk at birth may be an inherited character 
in women, and may not unfairly be looked upon in itself as a factor limiting fertility 
naturally. 
Taking these points into consideration, it seemed that if we were to have enough 
material to draw conclusions from we must entirely drop all attenipt to classify by 
age of parents at marriage. We might make some limitations but they must not be 
very stringent ; they must leave room for an increase of stringency in difterent 
directions, so that we could roughly appreciate the influence of the screening factors. 
Accordiugly our plan has been to show that correlation actually does exist between 
parent and oftspring with regard to fertility, and that when we make the conditions 
more stringent the correlation increases towards the value indicated by the law of 
ancestral heredity. 
(9.) Oti the Inheritance of Fertility in Woman. —(i.) Table I. gives the result for 
4418 cases of the fertility of a mother and of her daughter. These were extracted 
from Foster’s ‘ Peerage and Baronetage,’ Burke’s ‘ Landed Gentry,’ some family 
* As Duncan points out, an early marriage ou tlie average means an earlier ce.ssation of fecundity; a 
somewhat later one does not necessarily connote less fertility. 
