PACKARD. — INHERITANCE OF ACQUIRED CHARACTERS. 369 



the formation of new structures (Dohru), the effects of parasitism, 

 commensalism, and of symbiosis, in short the biological environment ; 

 together with geological extinction, natural and sexual selection, and 

 hybridity. 



It is to be observed that the Neolamarckian in relying mainly on 

 these factors does not overlook the value of natural selection as a 

 guiding principle, and which began to act as soon as the world became 

 stocked with the initial forms of life, but he simply seeks to assign this 

 principle to its proper position in the hierarchy of factors. 



Natural Selection, as the writer from the first has insisted, is not a 

 vera causa, an initial or impelling cause in the origination of new 

 species and genera. It does not start the ball in motion ; it only so 

 to speak guides its motions down this or that incline. It is the expres- 

 sion, like that of " the survival of the fittest" of Herbert Spencer, of 

 the results of the combined operation of the more fundamental fac- 

 tors. In certain cases we cannot see any room for its action ; in some 

 others we cannot at present explain the origin of species in any other 

 way. Its action increased in proportion as the world became more and 

 more crowded with diverse forms, and when the struggle for existence 

 had become more unceasing and intense. It certainly cannot account 

 for the origination of the different branches, classes, or orders of or- 

 ganized beings. It in the main simply corresponds to artificial selec- 

 tion ; in the latter case, man selects forms already produced by domes- 

 tication, the latter affording sports and varieties due to change in the 

 surroundings, that is, of soil, climate, food, and other physical features, 

 as well as education. 



In the case also of heredity, which began to operate as soon as the 

 earliest life forms appeared, we have at the outset to invoke the prin- 

 ciple of the heredity of acquired characters during the lifetime of 

 the lowest organisms. 



Finally, it is noticeable that when one is overmastered by the dogma 

 of natural selection he is apt, perhaps unconsciously, to give up all 

 effort to work out the factors of evolution, or to seek to work out this 

 or that cause of variation. Trusting too implicitly to the supposed 

 vera causa, one may close his eyes to the effects of change of environ- 

 ment or to the necessity of constant attempts to discover the real 

 cause of this or that variation, the reduction or increase in size of 

 this or that organ ; or become insensible to the value of experiments. 

 Were the dogma of natural selection to become universally accepted, 

 further progress would cease, and biology would tend to relapse into a 

 stage of atrophy and degeneration. On the other hand a revival of 

 vol. xxix. (n. s. xxi.) 24 



