410 NOTES. 



This idea at first seems striking;, but it is opposed alike to the facts, and 

 to the laws of mechanics. 



Nate 6,i)age 37. With reference to the constancy of such characters 

 as have arisen under external influences, Sachs says, in his Text-hooli of 

 Botany : ' We may infer very decidedly that hereditary characters, or 

 such as might become hereditary, are not produced by external 

 elementary influences, from the fact that seeds from the same fruit 

 produce several varieties, or one variety side by side with the here- 

 ditary parent-form ; ' and further on : ' We come to the conclusion that 

 hereditary varieties first arise independently of direct external in- 

 fluences, but that the possibility of their continued existence depends 

 on such influences.' There can certainly be no doubt that a great 

 number of modifications which are in a high degree hereditary were 

 due to causes which — like sexual reproduction and hybridisation — we 

 are not accustomed to designate as external influences, although I 

 reckon them as such ; and it is equally little doubtful that those con- 

 ditions which are universally recognised as external — such as climate, 

 nutrition, the nature of the soil, &c. — are able to acquire a modifying 

 influence on living and growing animals ; thus the modifications called 

 forth by such causes must constantly recur as long as the causes them- 

 selves remain constant. In the course of our investigations I shall have 

 occasion to discuss a few examples which may be regarded as having a 

 direct bearing on this. So far as I know, it was Helmholtz who first 

 pointed out that the constancy of an altered condition of life must 

 result in the permanence of any deviation from the parent form of the 

 species — or of the organ — to which such an alteration had given rise. 



Note 1 , page Z?i. I need here adduce only a few quotations. 'There 

 can be no doubt that changed conditions induce an almost indefinite 

 amount of fluctuating variability by which the whole organisation is 

 rendered in some degree plastic ' (Darwin, Descent of Man, i. 114). 

 ' Such changes are manifestly due, not to any one pair, but all the indi- 

 viduals having been subjected to the same conditions ' (Darwin, ibid., 

 in speaking of horses, page 236) ; and finally, ' We do not know what 

 produces the numberless slight difierences between the individuals of 

 each species, for reversion only carries the problem a few steps back- 

 wards ; but each peculiarity must have had its own efficient cause. If 

 these causes, whatever they may be, were to act more uniformly and 

 energetically during a lengthened period (and no reason can be 

 assigned why this should not sometimes occur), the result would pro- 

 bably be not mere slight individual difPerences, but well-marked, con- 

 stant modifications (ibid. p. 1 53). And in other places in the same 

 book, as well as in his other works, Darwin expresses himself in a way 

 that proves that he no longer rates the influence of the conditions of 

 life (external causes) on the transformation of forms (in species as 

 in organs) so low as he seemed to do in the first edition of his Orifin 

 of Species 



