MENDELISM AND BIOMETRY 227 
nevertheless the few exceptions recorded by competent 
observers still require further examination before they 
can be accepted as invalidating the law in any single 
instance. 
The question naturally arises as to how far the Men- 
delian rule of inheritance agrees with or contradicts 
those estimations of hereditary values which have been 
arrived at by the labours of the biometricians. 
So long ago as 1902 Mr. G. Udny Yule endeavoured 
with some apparent success to reconcile the Mendelian 
results with those of biometry. Progress has been 
rapid during the last four years, and what we have now 
before us is rather the question of reconciling the bio- 
metrical conclusions with the firmly established facts 
of Mendelian inheritance. More recently Mr. Yule 
seems to have succeeded in performing this service for 
science, although the comments of other biometrical 
students upon his work have still to be awaited. 
In 1902 Yule considered the case of a pair of simple 
Mendelian characters, A and a, exhibited in a mixed 
population breeding together at random, in such a way 
that the total number of germ cells bearing A and a 
respectively might be regarded as equal in any genera- 
tion. In such a case it will always be an even chance 
whether a recessive parent will produce a dominant 
or a recessive child, because the chance of its gamete 
(a2) mating with A or a is the same. A knowledge 
of the ancestry of the recessive parent makes no 
difference to the result. Consequently the case of 
the pure recessive does not fall in with any possible 
theory of ancestral heredity. 
15—2 
