PRESIDENT’S ADDRESS. 23 
was received from one parent only, not more than half the offspring, © 
on an average, will inherit it. What is it that has so long prevented 
mankind from discovering such simple facts? Primarily the circum- 
stance that as man must have two parents it is not possible quite 
easily to detect the contributions of each. The individual body is a 
double structure, whereas the germ-cells are single. Two germ-cells 
unite to produce each individual body, and the ingredients they respec- 
tively contribute interact in ways that leave the ultimate product a 
medley in which it is difficult to identify the several ingredients. When, 
however, their effects are conspicuous the task is by no means impos- 
sible. In part also even physiologists have been blinded by the survival 
of ancient and obscurantist conceptions of the nature of man by which 
they were discouraged from the application of any rigorous analysis. 
Medical literature still abounds with traces of these archaisms, and, 
indeed, it is only quite recently that prominent horse-breeders have 
come to see that the dam matters as much as the sire. For them, 
though vast pecuniary considerations were involved, the old ‘ homun- 
culus’ theory was good enough. We were amazed at the notions 
of genetic physiology which Professor Baldwin Spencer encountered 
in his wonderful researches among the natives of Central Australia; 
but in truth, if we reflect that these problems have engaged the atten- 
tion of civilised man for ages, the fact that he, with all his powers 
of recording and deduction, failed to discover any part of the Mendelian 
system is almost as amazing. The popular notion that any parents 
can have any kind of children within the racial limits is contrary to 
all experience, yet we have gravely entertained such ideas. As I have 
said elsewhere, the truth might have been found out at any period 
in the world’s history if only pedigrees had been drawn the right 
way up. If, instead of exhibiting the successive pairs of progenitors 
who have contributed to the making of an ultimate individual, some 
one had had the idea of setting out the posterity of a single ancestor 
who possessed a marked feature such as the Habsburg lip, and showing 
the transmission of this feature along some of the descending branches 
and the permanent loss of the feature in collaterals, the essential 
truth that heredity can be expressed in terms of presence and absence 
must have at once become apparent. For the descendant is not, as he 
appears in the conventional pedigree, a sort of pool into which each 
tributary ancestral stream has poured something, but rather a con- 
glomerate of ingredient-characters taken from his progenitors in such 
a way that some ingredients are represented and others are omitted. 
_ Let me not, however, give the impression that the unravelling of 
such descents is easy. Even with fairly full details, which in the case 
of man are very rarely to be had, many complications occur, often 
preventing us from obtaining more than a rough general indication of 
