12 ORTHOGENETIC EVOLUTION IN PIGEONS. 



habitually assume that the evolution of an organ or character begins with an 

 ''infinitesimal rudiment," which has no way of emerging from its functionless state 

 except through minute chance variations in various directions. In this assumption 

 the problem is misconceived. The characters we meet with to-day have rarely, 

 if ever, arisen by direct evolution from useless rudiments. When we know enough 

 about a character to undertake to trace its genesis, the "rudiment" imagined to 

 lie so near recedes, and we are led on, not to a "beginning," but to an antecedent, 

 and if we are fortunate enough to be able to advance farther, we come to another 

 antecedent, and so on. The series of antecedents stretches ever as far as we can 

 see. As we repeat this experience with different characters, looking always for the 

 primordial rudiment, our childish faith in such "beginnings" gives way to the 

 conviction that the chase is led by a phantom. 



No one of our sense-organs, for example, can be traced to a rudiment, except 

 in the embryological sense. The eye of the vertebrate may appear as a rudiment 

 in the embryo, but no one can doubt that it has had a phylogenetic history, the 

 first term of which — if first there be — must have been very different from its present 

 embryonic rudiment. To assume that the eye began in some different variation 

 that fluctuated or mutated, chance-wise, into a state of incipient utility, and was 

 then developed in a direct line to its present stage of complex adaptations, either 

 gradually or per saltum, would be hardly more satisfactory than appealing to a 

 miraculous succession of miracles. It is impossible to believe that such a system 

 of harmonious coadaptations could ever arise by mutation; 4 and selection, although 

 playing a very important part in such achievements, is probably never equal to the 

 whole task. Without the assistance of some factor having more continuous direct- 

 ive efficiency, selection would fail to bring out of the chaos of chance variation, 

 or kaleidoscopic mutation, such progressive evolution as the organic world reveals. 



In order to show that such a factor is essential, and that it is actually present, 

 supplying the indispensable initial stages and holding the master hand in the 

 general direction of evolution, demonstrative evidence is, of course, required. Such 

 evidence lies in the history of specific characters. But how shall we approach such 

 a task, if no near-by rudiment is to be found as a starting-point? Rudiments and 

 premutations are alike illusory in this regard, for their beginning is always and 

 necessarily assumed to lie in the realm of the invisible and unknowable. If we are 

 to keep always on ground that is open to investigation, we must find our starting- 

 points in known stages. As the laws of nature are constant, it is not essential to 

 trace entire histories. If some chapters are sufficiently open to observation and 

 experiment to permit close study, we may hope, in some of the more favorable 

 cases, to read the phenomena in their natural order and to learn from what goes 

 on in one part of the history the factors that govern in all parts. 



The study of the problem of the origin of species resolves itself, therefore, ever 

 more clearly into exhaustive studies of single favorable characters, in the more 

 accessible portions of their history. For decisive evidence we must have characters 

 of a comparatively simple nature, the evolutional records of which, in every case, 

 are to be read in a considerable number of species of known common origin. 



1 Darwin frequently emphasized the same objection. In a letter to Asa Gray, referring to the orchids, he remarks: 

 "It is impossible to imagine so many coadaptations being formed, all by a chance blow." Weismann has shown in a 

 masterly manner how inadequate is the mutation theory to account for such phenomena. 



