Recent Advances in the Study of Heredity. 167 
the difference between merely reading or hearing about the results 
and seeing them, is not much greater than the difference between 
seeing them, and planning and carrying out and laboriously recording 
the results of the experiment. I propose therefore to confine myself 
to the exhibition of such instances as you can easily make for 
yourselves in the course of a few years. 
This, therefore, is my reason for laying such emphasis on 
the nature of the revolution in opinion which is now approaching 
completion. That this is the real turning point will not, I think, 
be denied. Without the recognition that all attempts to predict 
the results of a given mating based on a knowledge of the somatic 
character of the individuals mated and of their ancestors are futile, 
none of the progress made since the beginning of this century 
would have been possible. And it was only natural that, so long as 
the problem of inheritance which naturalists set themselves to 
solve was a fictitious one, no progress was made. 
It was failure to recognize that one of the most, if not the most, 
essential features of Mendel’s theory was that it was a germinal 
theory of inheritance ( i.e ., a theory to account for the manner in 
which the characters of organisms are represented in the 
germ-cells which produce them) that rendered the first reception 
of this theory so hostile. I am thinking of the criticism of 
this theory by Weldon. He concluded his critique 1 with the 
words “ The fundamental mistake which vitiates all work based 
upon Mendel’s method is the neglect of ancestry, and the attempt 
to regard the whole effect upon offspring, produced by a particular 
parent, as due to the existence in the parent of particular 
structural characters ; while the contradictory results obtained by 
those who have observed the offspring of parents apparently 
identical in certain characters show clearly enough that not only 
the parents themselves, but their race, that is their ancestry, must 
be taken into account before the result of pairing them can be 
predicted.” 
I think this sentence shows that the theory of inheritance in 
Weldon’s mind was closely similar in essence to what I have called 
the theory of ancestral contributions, the theory, namely, that the 
characters of offspring are determined by the characters both of their 
parents and ancestors. We see, at any rate, that in Weldon’s theory 
the somatic character of parents and ancestor are the data which 
enable us to to predict the characters of offspring. Whether 
1 Biometrika, I., p. 228. 
