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.^ 



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. AVe cannot, therefore, 

 accept any arguments against the agency of natural selection 

 which are based upon the opjiosite 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 Dar\Wn 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, 

 Avhich are inherited ; and from these, peculiar habits folloAV 

 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, 

 w^hile preserving only those animals which best served our 

 purpose in their peculiar faculties, instincts, or habits. 



^ 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 otlier 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. 



