Characters, Hereditary and Acquired. 101 



What he regarded as the inherited effects of use and 

 of disuse may be entirely due to the cessation of 

 selection in the case of our domesticated animals, 

 combined with an active reversal of selection in the 

 case of natural species. And in accordance with 

 this view is the fact that the degeneration of disused 

 parts proceeds much further in the case of wild 

 species than it does in that of domesticated varieties. 

 For although it may be said that in the case of wild 

 species more time has been allowed for a greater 

 accumulation of the inherited effects of disuse than 

 can have been the case with domesticated varieties, 

 the alternative explanation is at least as probable 

 that in the case of wild species the merely negative, 

 or passive, influence of the cessation of selection has 

 been continuously and' powerfully assisted by the 

 positive, or active, influence of the reversal of selection, 

 through economy of growth and the general advantage 

 to be derived from the abolition of useless parts *. 



The absence of any good evidence of this direct 

 kind in favour of use-inheritance will be rendered 

 strikingly apparent to any one who reads a learned 

 and interesting work by Professor Semper 2 . His 

 object was to show the large part which he believed 

 to have been played by external conditions of life in 

 directly modifying organic types or, in other words, 

 of proving that side of Lamarckianism which refers 

 to the immediate action of the environment, whether 

 with or without the co-operation of use-inheritance 

 and natural selection. Although Semper gathered 



1 For a fuller explanation of the important difference between the 

 mere cessation and the actual reversal of selection, see Appendix L 

 * Animal Life, International Scientific Series, vol. xxxi. 



