162 
A. D. Darbishire. 
great-grandparents, and so back. I propose to call this theory, for 
convenience of reference,“The Theory of Ancestral Contributions.” 1 
It follows from this theory that our ability to predict the result 
of a given mating depends on the extent of our knowledge of the 
ancestry, i.e., the somatic characters of the ancestors of the two 
forms mated. The attempt, which stands in such sharp contrast to 
the Mendelian method of procedure, “to breed out” an undesirable 
characteristic by breeding for many generations from individuals 
which do not manifest it, is based on a deeply rooted, though 
perhaps not definitely formulated, belief in this theory. The 
delusion that by breeding for a sufficiently large number of 
generations from an Andalusian Fowl (known now to be a hybrid 
form which will always throw blacks and “ splashed-whites ” in 
definite proportions) it will ultimately be possible to obtain a race 
of pure Andalusians, can only be due to a belief that the characters 
of offspring are determined by the somatic characters of their 
parents and ancestors to a diminishing extent as we proceed 
backwards. And really it involves some such theory as Pangenesis 
to account for it. But the practical breeder is not primarily con¬ 
cerned with the interpretation of the phenomena he witnesses, or 
with the scientific basis on whieh the principles which he follows 
are founded; all he requires is a principle which shall guide him to 
the end to which he wishes to attain. There is, however, not much 
difference between the practical breeder and pure biologist in the 
matter of the attention which either pays to the scientific explanation 
of this theory ; for the biologist is guilty of retaining a belief in the 
theory of ancestral contributions long after he has not merely 
formally given up his belief in the theory of Pangenesis, but after 
he has declared his allegiance to the principle involved in Weismann’s 
doctrine of the continuity of the germ-plasm, namely that inheritance 
is not from soma to soma, but from germ to germ. It is, in my 
opinion, important to recognize the reality and universality of a 
belief in the theory of ancestral contributions, because this theory, 
which is merely another name for what is called the common 
1 Whilst this lecture is going through the press, a paper, by 
Professor Pearson, entitled TheThcory of Ancestral Contributions 
in Heredity has appeared (Proc. Roy. Soc., Series B, Vol. 81, 
p. 219). I shall deal with the point raised by the author in a 
later lecture, but should like to state here that whilst I am in 
substantial agreement with Professor Pearson’s main con¬ 
tention, my “Theory of Ancestral Contributions” is a 
physiological theory of inheritance applicable to individuals, 
whilst the Law of Ancestry is a statistical generalization 
relating to masses, the component individuals of which mate 
at random. 
