xiv 
FUNDAMENTAL PROBLEMS 
441 
the resulting epilepsy, or a general state of weakness, de¬ 
formity, or sores, was sometimes inherited. It is, however, 
possible that the mere injury introduced and encouraged the 
growth of certain microbes, which, spreading through the 
organism, sometimes reached the germ-cells, and thus trans¬ 
mitted a diseased condition to the offspring. Such a transfer¬ 
ence of microbes is believed to occur in syphilis and tuberculosis, 
and has been ascertained to occur in the case of the muscardine 
silkworm disease. 1 
The Theory of Instinct. 
The theory now briefly outlined cannot be said to be 
proved, but it commends itself to many physiologists as being 
inherently probable, and as furnishing a good working 
hypothesis till displaced by a better. We cannot, therefore, 
accept any arguments against the agency of natural selection 
which are based upon the opposite and equally unproved 
theory that acquired characters are inherited; and as this 
applies to the whole school of what may be termed Neo- 
Lamarckians, their speculations cease to have any weight. 
The same remark applies to the popular theory of instincts 
as being inherited habits ; though Darwin gave very little 
weight to this, but derived almost all instincts from spontaneous 
useful variations which, like other spontaneous variations, are 
of course inherited. At first sight it appears as if the acquired 
habits of our trained dogs—pointers, retrievers, etc.—are 
certainly inherited; but this need not be the case, because 
there must be some structural or psychical peculiarities, such 
as modifications in the attachments of muscles, increased 
delicacy of smell or sight, or peculiar likes and dislikes, 
which are inherited ; and from these, peculiar habits follow 
as a natural consequence, or are easily acquired. Now, as 
selection has been constantly at work in improving all our 
domestic animals, we have unconsciously modified the structure, 
while preserving only those animals which best served our 
purpose in their peculiar faculties, instincts, or habits. 
1 In his essay on “ Heredity,” Dr. Weismann discusses many other cases 
of supposed inheritance of acquired characters, and shows that they can all 
be explained in other ways. Shortsightedness among civilised nations, for 
example, is due partly to the absence of selection and consequent regression 
towards a mean, and partly to its individual production by constant reading. 
