V20 
PROFESSOR K. PEARSON AND DR. A. LEE ON 
In order to illustrate the method, I chose two characters, coat-colour in horses and 
eye-colour in man, which seemed sufficiently diverse both as to origin and species A 
The new method enabled me to reach results for half-brethren, grandparents and 
uncles and aunts, which had not yet been independently considered. The conclu¬ 
sions arrived at for eye-colour in man at no point conflict with those for coat-colour 
in horses, and both in the main accord with the theory of exclusive inheritance with¬ 
out reversion herein developed. We find— 
(i.) No approach to a single value for the coefficient of inheritance for each grade 
of relationship; it varies widely with the sex, and the line through which the 
relationship is traced. 
(ii.) No approach in average values to those which would be indicated by Mr. 
Galton’s Law. 
Nor does the modification of Mr. Galton’s Law, which I have termed the Law of 
Ancestral Heredity, give better results. For, if we cause it to give the parental 
values, it then renders results inconsistent with the fraternal values. 
(iii.) There is agreement with the theory of exclusive inheritance without reversion 
for the parental, avuncular and fraternal series ; but there is some anomaly in the 
case of grandparental inheritance. This requires further investigation, and possibly 
a modification of our views on the nature of reversion. 
We want a list formed of characters in various types of life, which are supposed to 
be exclusively inherited, and then experiments ought to be made and statistics col¬ 
lected with regard to these characters. It is in this field of exclusive inheritance 
that we must look for real light on the problem of reversion. 
If we consider the three known forms of inheritance, the blended, the exclusive, 
and the particulate (which may possibly be combined in one individual, if we deal 
with different organs); if we consider further that these forms may possibly have to 
be supplemented by others not yet recognised (e.g., reversional theories depending, 
say, on heterogamous unions), then it would appear that the time is hardly ripe even 
for provisional mechanical theories of heredity. What we require to know first is, 
the class of organs and the types of life for which one or other form of inheritance 
predominates. As variation in no wise depends on the existence of tivo germ-plasms, 
so biparental heredity can by no means be treated as the result of their simple quanti¬ 
tative mixture ; the component parts of these germ-plasms corresponding to special 
characters and organs, must he able to act upon each other in a variety of qualita¬ 
tively different ways. To adopt for a moment the language of Darwin’s theory of 
pangenesis, the multiplying gemmules from an organ in the father must (i.) cross with 
gemmules from that organ in the mother, and the hybrid gemmules give rise to 
blended inheritance, (ii.) must without crossing multiply alongside the gemmules of 
the mother, and give rise to particulate inheritance, (iii.) must alone survive, or alone 
* Since supplemented by my investigations, based on Mr. Gai.ton’s data, for coat-colour in hounds, 
‘ Roy. Soc. Proc.,’ vol. 6G, p. 140 et seq. 
