Januaby 23, 1920] 



SCIENCE 



75 



It may be that the emphasis laid on unit- 

 character by some of the earlier enthusiastic 

 followers of Mendel and the frequent confu- 

 sion in their writings between the unit-char- 

 acter, so-called, and the change in the germ- 

 plasm that gave rise to it, may justify Whit- 

 man's scepticism; but this charge can hardly 

 be brought against de Vries, who stated over 

 and over again that a single change in the 

 germ-plasm may be the cause of manifold 

 although slight changes in the characters 

 throughout the whole organism. 



In contrast to change by mutation Whit- 

 man opposes orthogenesis. Evidence for the 

 latter he finds in his study of the group of 

 pigeons. The evidence is the familiar argu- 

 ment from comparative anatomy and from 

 the hypothesis of " recapitulation."^ Before 

 taking up the evidence I can not refrain from 

 quoting a fine and characteristic statement of 

 Whitman's in the same lecture: 



" I take exception here only to the implica- 

 tion that a definite variation-tendency must 

 be considered teleological because it is not 

 ' orderless.' I venture to assert that variation 

 is sometimes orderly and at other times 

 rather disorderly, and that the one is just as 

 free from teleology as the other. In our 

 aversion to the old teleology, so effectually 

 banished from science by Darwin, we should 

 not forget that the world is full of order, the 

 organic no less than the inorgatiic. Indeed 

 what is the whole development of an organism 

 if not strictly and marvelously orderly? Is 

 not every stage, from the primordial germ 

 onward, and the whole sequence of stages, 

 rigidly orthogenetic ? If variations are devia- 

 tions in the directions of the developmental 

 processes what wonder is there if in some 

 directions there is less resistance to varia- 

 tion than in others? What wonder if the 



2 Whitman uses the word ' ' recapitulation ' ' in the 

 sense for which the reviewer argued in 1903 ("Evo- 

 lution and Adaptation," Chap. III.). As so used 

 it means something essentially different from the 

 word "recapitulation" in the original sense of 

 Darwin and Haeckel, unless the changes in the 

 germ-plasm add Stages only to the end of ontogeny 

 as Whitman seems to think is the way in which 

 the process takes place. (See a later footnote.) 



organism is so balanced as to permit both 

 unifarious and multifarious variations? If a 

 developmental process may run on throughout 

 life (e. g., the lifelong multiplication of the 

 surface-pores of the lateral-line system in 

 Amia) what wonder if we find a whole species 

 gravitating slowly in one or a few directions? 

 And if we find large groups of species all 

 affected by a like variation, moving in the 

 same direction, are we compelled to regard 

 such ' a definite variation-tendency ' as teleo- 

 logical, and hence out of the pale of science? 

 If a designer sets limits to variation in order 

 to reach a definite end, the direction of events 

 is teleological; but if organization and the 

 laws of development exclude some lines of 

 variation and favor others there is certainly 

 nothing supernatural in this, and nothing 

 which is incompatible with natural selection. 

 Natiiral selection may enter at any stage of 

 orthogenetic variation, preserve and modify 

 in various directions the results over which it 

 may have had no previous control." 



How far one is justified in extending the 

 orderly sequence of embryonic development to 

 the sequence shown in evolutionary advance 

 is a large question and will no doubt be 

 settled some day by fuller knowledge. At 

 present our speculations must rest on the 

 evidence at hand, and this evidence. Whitman 

 finds, as stated, in his comparative studies of 

 pigeon coloration, and in a most ingenious 

 experiment of feather plucking. 



His studies of domesticated breeds and their 

 wild relatives led him to conclude that the blue 

 wing with two black bars is not the original 

 pattern as Darwin supposes, but rather the 

 checkered wing covered with black spots. 

 Both patterns are found to-day in wild birds, 

 hence these birds can not be appealed to for a 

 decision. But an examination of other spe- 

 cies of pigeons shows that the checkered type 

 is widespread and occurs in many varieties; 

 and the young in many groups show a more 

 checkered pattern than do the adults them- 

 selves. The Japanese turtle dove comes near- 

 est, in Whitman's opinion, to the original type 

 of wing pattern. The elaborate consideration 

 that Whitman devotes to the subject indicates 

 how important the question appeared to him; 



