Recent Advances in the Study of Heredity. 175 
who have given expositions of Mendelian doctrine do not clearly 
distinguish between what, on the theory, we expect will happen and 
what actually does. One author for instance, referring to the 
production of recessives in definite proportions says that the hybrids 
“ will repeat the process and proportions practically for ever.” 
Let us now examine the Mendelian phenomenon displayed in 
the diagram on p. 172 in the light of the theory of ancestral contri¬ 
butions. Two of the things which happen are contrary to the 
expectation based on that theory; one is the unexpected breeding 
true of all the greens and one-third of the yellows which appear in 
F 2 : the fact, however, that the offspring of these forms continue 
to breed true in subsequent generations becomes more in accordance 
with expectation based on the ancestral theory as we proceed away 
from F t . On the other hand whilst the production, by the remaining 
two-thirds of the yellows, of yellows and greens in the ratio 3:1, does 
not give cause for much surprise when it occurs in F 2 , the fact that 
these hybrid yellows continue to do so for six generations becomes 
more remarkable ( i.e ., less in accordance with the contributional 
theory) in each successive generation as we proceed further 
from F x . 
It is seen therefore that the Mendelian phenomenon itself 
strongly negatives any theory of inheritance according to which the 
characters of a given generation are determined by the somatic 
character of its parents and, in a diminishing degree, of its ancestors. 
That these somatic characters play no part at all in determining the 
characters of progeny is an entirely novel conception, the acceptance 
of which is due in large part, as I have suggested, to the combined 
weight of the work done by Weismann and Mendel. 
I think it will be desirable therefore to place before you the 
result of an experiment 1 which proves in regard to the pair of 
characters (yellow and green) before us, that the somatic characters 
of parents and ancestors play no part in determining the nature of 
their offspring. 
The precise point which the following experiment was designed 
to test was whether the ancestry of the recessive parent of the 
cross could have any effect on the result of the cross. The recessive 
parent of the cross was chosen because (in virtue of the fact that 
two yellows may produce greens, whilst two greens never produce 
yellows) it is possible to adulterate the ancestry of the green parent 
with the yellow character to a much greater extent than it is possible 
1 An Experimental Estimation of the Theory of Ancestral Contri¬ 
butions in Heredity. Proc. Roy. Soc. B., Vol. 81, 1909, p. 61. 
