ON HEREDITY. 1)1)6 



potentiality so varied, tlint all llie. iiinltiforni variations in physical 

 strnctuie, tendency to disease, teuipeiameiit, and other characters and 

 dispositions which have been exhibited by all the races and varieties of 

 men who either now inhabit, or at any period in the world's history have 

 inhabited, the earth ninst have been included in it. - - - 



Let us now glance at the other side of the question. All biologists 

 will, I suppose, accept the propositioi] that the individual soma is intlu- 

 enced or modified by its environments or surroundings. Now, if ou the 

 basis of this proposition, the theory be grafted that modifications or vari- 

 ations thus produced are capable of so affecting the gerin-plasra of the 

 individual in whom the variation arises as to be transmitted to its off- 

 spring (and I have already given cases in point), then such variations 

 might be perpetuated. If the modification is of service, then presum- 

 ably it will add to the vitability of the individual, and through the 

 inter-action between the soma and the germ-plasm, in connection with 

 their respective nutritive changes, will so affect the latter as to lead to 

 its being transmitted to the offspring. From this point of view the en- 

 vironment would, as it were, determine and regulate the nature of those 

 variations which are to become hereditary, and the possibility of varia- 

 tions arising which are likely to prove useful becomes greater than on 

 the theory that the soma exercises no influence on the germ-plasm. 

 Hence I am unable to accept the proposition that somatogenic charac- 

 ters are not transmitted, and I can not but think that they form an 

 important factor in the production of hereditary characters. 



The morphological aspect of organic structure is undoubtedly of fun- 

 damental imi)ortance. . But it should not be forgotton that tissues and 

 organs — in addition to their subjection to the principles of development 

 and descent — have to discharge certain specific purposes and functions, 

 and that structural modifications arise in them in correlation with the 

 uses 10 which they are put, so as to adoi)t them to perforin modified 

 duties. It may be difficult to assign the exact force which physiologi- 

 cal adaptation can exercise in the peri)etuation of variations. If the 

 habit or external condition which has produced a variation continues 

 to be practiced, then in all probability the variation would be intensi- 

 fied in successive generations. But should the habit cease or the 

 external condition be changed, then although the variation might con- 

 tinue to be for a time perpetuated by descent, it would i)robably be- 

 come less strongly marked and i)erhaps ultimately disai)i)ear. By :u'.- 

 cepting the theory that somatogenic characters are transmitted we 

 obtain a more ready explanation, how men belonging to a race living in 

 one clinnite or part of the globe can adapt themselves to a climate of a 

 different kind. On the theory of the non-transmissibility of these ac- 

 (juired characters, long periods of years would have to elapse before the 

 ])rocess of adaptation could be effected. The weaker exami)les (on this 

 theory) would have had to die out, and the racial variety would require 

 to have been produced by the selection of variations arising slowly and 



