OTHER THEORIES OF SPECIES-FORMING 267 
dwarfed in size. The relative sizes of the parts were unaltered, show- 
ing that there had been no real struggle among the determinants; for, 
on the theory of germinal selection, only the stronger determinants 
would have survived and the weaker ones would have been starved 
out. Partial individuals, moreover, lacking certain organs and over- 
developed in others, would have been produced instead of individuals 
merely smaller in all parts. 
These are the specific objections to the theory, but more important 
than all of these is the general objection that follows: 
“Thus Weismann,” says Morgan, “has piled up one hypothesis 
on another as though he could save the integrity of the theory of 
natural selection by adding new speculative matter to it. The most 
unfortunate feature is that the new speculation is skilfully removed 
from the field of verification, and invisible germs whose sole functions 
are those which Weismann’s imagination bestows on them, are brought 
forward as though they could supply the deficiencies of Darwin’s 
theory. This is, indeed, the old method of the philosophizers of 
nature. An imaginary system has been invented which attempts to 
explain all difficulties, and if it fails, then new inventions are to be 
thought of. Thus we see where the theory of selection of fluctuating 
germs has led one of the most widely known disciples of the Darwin- 
ian theory. 
“The worst feature of the situation is not so much that Weismann 
has advanced new hypotheses unsupported by experimental evidence, 
but that the speculation is of such a kind that it is, from its very 
nature, unverifiable, and therefore useless. Weismann is mistaken 
when he assumes that many zodlogists object to his methods because 
they are largely speculative. The real reason is that the speculation is 
so often of akind that cannot be tested by observation and experiment.” 
It seems almost impossible that the same Professor Morgan, who 
wrote the foregoing paragraphs in 1903, should now be the leading 
exponent of a theory of the mechanics of. hereditary transmission 
which depends upon hereditary units almost identical with Weis- 
mann’s ‘‘determinants,” for the “genes” or “factors” of Morgan are 
minute corporeal bodies in the germ cells which determine the charac- 
ters of the adult individual. , 
The difference is, however, that the ‘‘genes”’ of Morgan are experi- 
mentally demonstrable and have behind them a vast amount of real 
evidence for their existence. 
« From T. H. Morgan, Evolution and Adaptation. 
