November 20, 1896.] 



SCIENCE. 



735 



live variations are independent of adaptive 

 modifications. 



Now, what is natural selection, at any 

 rate as understood by the master — Darwin ? 

 It is a process whereby, in the struggle for 

 existence, individuals possessed of favorable 

 and adaptive variations survive and hand 

 on their good seed, while individuals pos- 

 sessed of unfavorable variations succumb, 

 are sooner or later eliminated, standing 

 therefore a less chance of begetting offspring. 

 This is the natural selection of Darwin. 

 But it is clear that to make the difference 

 between survival and elimination the favor- 

 ableness of the variation must reach a cer- 

 tain amount — varying with the keenness of 

 the struggle. This was termed by Ro- 

 manes 'selection value.' And one of the 

 difficulties which critics of natural selection 

 have felt is that the little more or the lit- 

 tle less of variation must often be too small 

 in amount to be of selection value so as to 

 determine survival. This difficulty is ad- 

 mitted by Prof. Weismann as a real one. 

 " The Lamarckians were right," he says, 

 '^ when they maintained that the factor for 

 which hitherto the name of natural selection 

 had been exclusively reserved, viz., personal 

 selection \i. e., the selection of individuals] , 

 was insufficient for the explanation of the 

 phenomena." * And again : f " Something 

 is still wanting to the selection of Darwin 

 and Wallace, which it is obligatory on us 

 to discover, if we possibly can." 



The additional factor which Dr. Weis- 

 mann suggests is what he terms germinal 

 selection. This, briefly stated, is as follows : 

 There is a competition for nutriment among 

 those parts of the germ from which the 

 several organs or groups of organs are de- 

 veloped. These he names determinants; 

 in this competition the stronger determi- 

 nants get the best of it, and are further 

 developed at the expense of the weaker 



* Germinal Selection, Monist Jan., 1896, p. 290. 

 t Op cit. p. 264. 



determinants, which are starved and tend 

 to dwindle and eventually disappear. The 

 suggestion is an interesting one, but one 

 well-nigh impossible to put to the test of 

 observation. It must at present be placed 

 among the 'may-bes' of biology. If ac- 

 cepted as a factor, it would serve to account 

 for the existence of determinate variations, 

 that is to say, variations along special or 

 particular lines of adaption. 



Such determinate variations are, how- 

 ever, explicable on the theory of natural 

 selection — a term which, in my opinion, 

 should be reserved for that process of indi- 

 vidual survival and elimination to which it 

 was applied by Darwin, Writing in 1892 

 I put the matter thus :* " Take the case of 

 an organism which has in some way 

 reached harmony with its environment. 

 Slight variations occur in many directions, 

 but these are bred out by intercrossing. It 

 is as if a hundred pendulums were swing- 

 ing just a little in many directions, but 

 were at once damped down. Now, place 

 such an organism in changed conditions. 

 The swing of one or two of the pendulums 

 is found advantageous; the organisms in 

 which these two pendulums are swinging 

 are selected ; they mate together and in 

 their offspring, while these two pendulums 

 are by congenital inheritance kept a- swing- 

 ing, the other 98 pendulums are rapidly 

 damped down as before. 



" Let us suppose, then, that the variation 

 in tooth structure, in a certain mechanically 

 advantageous direction, be such a selected 

 pendulum swing. That particular pendu- 

 lum, swinging in that particular direction, 

 will be the subject of selection. The other 

 pendulums will still be damped down as 

 before, and in that particular pendulum 

 variations from the particular direction 

 will be similarly damped down. It will 

 wobble a little, but its wobbling will be as 

 nothing compared with the swing that is 



* Natural Science, Vol. I., April, 1892, pp. 100-101. 



