22, PRESIDENT’S ADDRESS. 
uppermost in our minds is that knowledge of the nature of life is 
altogether too slender to warrant speculation on these fundamental 
subjects. Did we presume to offer such speculations they would 
have no more value than those which alchemists might have made as 
to the nature of the elements. But though in regard to these 
theoretical aspects we must confess to such deep ignorance, enough has 
been learnt of the general course of heredity within a single species to 
justify many practical conclusions which cannot in the main be shaken. 
I propose now to develop some of these conclusions in regard to our 
own species, Man. 
In my former Address I mentioned the condition of certain animals 
and plants which are what we call ‘ polymorphic.’ Their populations 
consist of individuals of many types, though they breed freely together 
with perfect fertility. In cases of this kind which have been suffi- 
ciently investigated it has been found that these distinctions—some- 
times very great and affecting most diverse features of organisatioun— 
are due to the presence or absence of elements, or factors as we call 
them, which are treated in heredity as separate entities. | These 
factors and their combinations produce the characteristics which we 
perceive. No individual can acquire a particular characteristic unless 
the requisite factors entered into the composition of that individual 
at fertilisation, being received either from the father or from the 
mother or from both, and consequently no individual can pass on to 
his offspring positive characters which he does not himself possess. 
Rules of this kind have already been traced in operation in the human 
species; and though I admit that an assumption of some magnitude 
is involved when we extend the application of the same system to 
human characteristics in general, yet the assumption is one which 
I believe we are fully justified in making. With little hesitation we 
can now declare that the potentialities and aptitudes, physical as well 
as mental, sex, colours, powers of work or invention, liability to 
diseases, possible duration of life, and the other features by which the 
members of a mixed population differ from each other, are determined 
from the moment of fertilisation; and by all that we know of heredity 
in the forms of life with which we can experiment we are compelled 
to believe that these qualities are in the main distributed on a factorial 
system. By changes in the outward conditions of life the expression 
of some of these powers and features may be excited or restrained. 
For the development of some an external opportunity is needed, and 
if that be withheld the character is never seen, any more than if the 
body be starved can the full height be attained; but such influences 
are superficial and do not alter the genetic constitution. 
The factors which the individual receives from his parents and no 
others are those which he can transmit to his offspring; and if a factor 
