loo NATURAL SCIENCE. ^,^„ 



Tertiaries being in this respect quite unrivalled in the known world. 

 Of the better known species, the collections already contain hundreds, 

 and sometimes thousands, of individuals available for study 

 [and by implication, I presume, actually studied] . If results obtained 

 from such material point in one direction, it is surely most illogical 

 to assume that specimens yet to be discovered will probably lead to 

 opposite conclusions. The probabilities are all the other way. . . . 

 That individuals in the early stages of life are uncommon as fossils 

 is very far from being the case. They are abundantly represented 

 in the collections, and show no more tendency to indeterminate 

 variation than do the adults. But even were the young stages un- 

 known, before their absence could be allowed weight as an objection, 

 it would be necessary to show that such very slight changes were of 

 * elimination value.' '" 



It is not my intention here to urge again my previous criticism. 

 Personally, I also am disposed to question whether such very slight 

 changes would be of what I have termed " elimination value," that 

 is, whether they would be fatal in life's competition; but the thorough- 

 going believer in Natural Selection as the sole factor in evolution does 

 not accept my " elimination value." He says all unfavourable 

 variations, no matter how slight, are eliminated ; and it is he that we 

 have to convince. From his point of view, then, I am still somewhat 

 doubtful whether the material already studied is sufficient to justify 

 the assertion that unfavourable variations in the budding stage (i.e., 

 scarcely recognisable, or deemed of no consequence by the palaeonto- 

 logist, but readily picked out by the "ever-vigilant eye" of Natural 

 Selection) do not occur. 



Granting, however, that my criticism Avas ill-founded — and it 

 should be remembered that I was criticising the view to which I 

 myself lean — it seems to me probable that, on the selection hypo- 

 thesis, determinate variations in the direction of mechanical 

 adaptations would far outnumber other variations in other directions. 

 Take the case of an organism which has in some way reached 

 harmony with its enxironment. Slight variations occur in many 

 directions, but these are bred out by intercrossing. It is as if a 

 hundred pendulums were swinging 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-swinging,the other 98 pendulums are rapidly damped down as before. 

 Let us suppose, then, that the variation of tooth structure, in a 

 certain mechanically advantageous direction, be such a selected 

 pendulum swing. That particular pendulum, swinging in that 

 particular direction, will be the subject of selection. The other 

 pendulums will still l>e damped down as before, and in tliat particular 



