Deiinlte Variation 99 



fertile on the female side, and some on the male side also, but the 

 hybrids produced between the Turnip (Brassica napiis) and the 

 Swede (Brassica campestris), which, according to our estimates of 

 affinity, should be nearly allied forms, are totally sterile \ Lastly, it 

 may be recalled that in sterility we are almost certainly considering a 

 meristic phenomenon. Failure to divide is, we may feel fairly sure, 

 the immediate " cause " of the sterility. Now, though we know very 

 little about the heredity of meristic differences, all that we do know 

 points to the conclusion that the less-divided is dominant to the 

 more-divided, and we are thus justified in supposing that there are 

 factors which can an-est or prevent cell-division. My conjecture 

 therefore is that in the case of sterility of cross-breds we see the 

 effect produced by a complementary pair of such factors. This and 

 many similar problems are now open to our analysis. 



The question is sometimes asked. Do the new lights on Variation 

 and Heredity make the process of Evolution easier to understand? 

 On the whole the answer may be given that they do. There is some 

 appearance of loss of simplicity, but the gain is real. As was said 

 above, the time is not ripe for the discussion of the origin of species. 

 With faith in Evolution unshaken — if indeed the word faith can be 

 used in application to that which is certain — we look on the manner 

 and causation of adapted differentiation as still wholly mysterious. 

 As Samuel Butler so truly said : " To me it seems that the ' Origin of 

 Variation,' whatever it is, is the only true 'Origin of Species'"^, and 

 of that Origin not one of us knows anything. But given Variation — 

 and it is given : assuming further that the variations are not guided 

 into paths of adaptation — and both to the Darwinian and to the 

 modern school this hypothesis appears to be sound if unproven — an 

 evolution of species proceeding by definite steps is more, rather than 

 less, easy to imagine than an evolution proceeding by the accumulation 

 of indefinite and insensible steps. Those who have lost themselves in 

 contemplating the miracles of Adaptation (whether real or spurious) 

 have not unnaturally fixed their hopes rather on the indefinite than 

 on the definite changes. Tlic reasons are obvious. By suggesting 

 that the steps through which an adaptative mechanism arose were 

 indefinite and insensible, all further trouble is spared. AVhile it 

 could be said that species arise by an insensible and imperceptible 

 process of variation, there was clearly no use in tiring ourselves by 

 trying to perceive that process. This labour-saving counsel found 

 ureat favour. All that had to be done to develop evolution-theory 

 was to (liHCOver the good in everything, a task which, in the complete 

 absence of any control or test whereby to check the truth of the 



* See Sutton, A. W., Jouru. Linn. Soc. xxxviii. p. 341, 1908. 

 » Life nnd Habit, London, p. 2G3, 1878. 



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