314 
PROFESSOR KARL PEARSON AND AIR. LESLIE BRAMLEY-MOORE, 
is not demonstrated, but may be treated as probable until the results of further 
investigations—preferably by breeding experiments instituted for this very purpose— 
are available. 
( 18 .) Conclusion. —The investigations of this memoir have been to some extent 
obscure and difficult, but the general result is beyond question. 
Fertility and fecundity, as shown hy investigations on mankind and on the 
thoroughbred horse, are inherited characters. 
The laws of inheritance of these characters are with considerable probability those 
already developed in my memoir on the Law of Ancestral Heredity for the inherit¬ 
ance of directly measurable organic characters. 
In the course of the work it has been shown how a numerical measure may be 
obtained for the inheritance of a character by one sex from the other, when it is 
patent in the former and latent in the latter. Fertility and fecundity purely latent 
in the male (in the sense here used) are shown to be transferred by him from his 
mother to his daughter. Thus Darwin’s views with regard to the transmission 
through one sex of a character peculiar to tlie other are given a quantitative 
corroboration.'" 
When we turn from these points to their weight and importance for the theory of 
evolution, we are at once encountered by all the wide-reaching principles which flow 
from the demonstration that genetic (reproductive) selection is a true factor of 
development. Let us look at these a little more closely. 
If natural selection were to be absolutely suspended, i.e., if there were no 
differential death-rate at all, then development would not for a moraejit cease. Not 
only is fertility inherited, but there can be small doubt that it is closely correlated 
with all sorts of organic characters ; thus the inheritance of fertility marks, the 
moment natural selection is suspended, a progressive change in a great variety of 
orpfanic characters. Without a differential death-rate the most fertile will form in 
every generation a larger and larger percentage of the whole population. There are 
very few characters which may not be supposed to be more or less directly correlated 
with fertility, and in reproductive selection we see a cause of progressive change 
continuously at work.t There is, so to speak, in every species an innate tendency 
to progressive change, quantitatively measurable by determining the correlation 
coefficients between fertility and organic characters, and between fertility in the 
parents and in the offspring. This “innate tendency” is no mysterious “force” 
causing evolution to take place in a pre-ordained direction ; it is simply a part of the 
physical organisation of the individual, which does not leave fertility independent of 
* The method is perfectly general, and a value can always be found for the intensity of transmission 
of a sexual character through the opposite sex. We could obtain, for example, a numerical measure of 
the manner in which a bull transmits good milking qualities to its offspring. 
t I have endeavoured to show (‘ Roy. Soc. Proc.,’ vol. 59, p. 303), that fertility is correlated with 
stature in woman. I hope later to return to the correlation of fertility and physique. 
