Decembee 7, 1906.] 



SCIENCE. 



729 



what Waagen ' called ' mutation/ a term tliat 

 has been accepted and frequently used by 

 paleontologists (for instance Neumayr/ W. 

 B. Scott' and also the present writer^). The 

 same idea is implied in Elmer's term ' ortho- 

 genesis/ * which has also been used by subse- 

 quent writers.* Thus, ' other terms being 

 available/ " there is absolutely no need to ac- 

 cept the confusing change of the meaning of 

 the word ' evolution.' 



Dr. Cook holds, that ' evolution ' (correctly, 

 according to the rule of priority, ' mutation,' 

 Waagen) is made possible by two factors, 

 * heterism ' (the normal diversity of individ- 

 uals) and ' symbasis ' (interbreeding = amphi- 

 mixis, Weismann). This is by no means cor- 

 rect, for it is unintelligible how interbreeding 

 of different individuals should be able to re- 

 sult in a ' progressive change ' of the species. 

 Amphimixis only serves to maintain the aver- 

 age of a number of individuals, which vary 

 around this average," and, moreover, it is not 

 an absolutely necessary factor in evolution 

 (old sense), which is evident at once, when 



* ' Die Formenreihe des Ammonites subradiatus,' 

 in Benecke's ' Geogn.-Palseontol. Beitr./ 2, pp. 

 179-256. 



* ' Die Staemme des Thierreiehs.' 1, 1889, pp. 

 60, 61. 



• ' On the Osteology of Mesohippus and Lepto- 

 meryx, with Observations on the Modes and Fac- 

 tors of Evolution in the Mammals/ in Journ. 

 Morphol., 5, 1891, p. 387, 388. 'On Variations 

 and Mutations,' in Amer. Journ. Sci., 48, 1894, 

 p. 355. 



' ' Grundziige der marinen Tiergeographie,' 

 1896, pp. 30, 31. 'On Natural Selection and 

 Separation/ in Pr. Amer. Phil. 8og., 35, 1896, p. 

 176. 



* ' Die Artbildung und Verwandtschaft bei den 

 Sehmetterlingen/ 2, 1895, p. 3. ' Orthogenesis 

 der Schmetterlinge,' 1897, pp. i-xii. 



* For instance, quite recently by Paul Sarasin, 

 in Verh. deutsch, zool. Ges., 1906, p. 137. 



" Ortmann, . in Science, I. c, p. 668. ' Trans- 

 formation ' might also answer ; it corresponds to 

 the German ' Umwandlung,' as used by PfeflFer. 



" See Ortmann, in Biolog. Centralblatt, 18, 1898, 

 pp. 146-149. (In opposition to Weismann's view 

 of the action of amphimixis; see Weismann, 'Am- 

 phimixis/ 1891.) 



we consider that there are organic forms, 

 which lack sexuality. 



As to the real causes of mutation (Waagen) 

 I refer to my discussion of this subject in a 

 previous paper," which in the main accepts 

 the views set forth by Pfeffer in a special 

 treatise on this question." According to this, 

 mutation of a species, its transformation in 

 time, is the evolutionary process restricted to 

 a single species ; it includes all factors of evo- 

 lution (old sense) except one, segregation, 

 which, when added, causes the splitting up of 

 one species into two or more. 



With reference to my belief that acquired 

 characters are transmitted, and that all varia- 

 tion is due to environment. Dr. Cook main- 

 tains that ' heterism,' the diversity of co- 

 existing individuals, is 'normal,' that is to 

 say, an innate quality of organisms, and he 

 asserts that there are no facts which sup- 

 port the doctrine that conditions of environ- 

 ment cause this diversity. I recommend to 

 him to read again the last two paragraphs of 

 my article," and further, what I have said on 

 these topics elsewhere," for he has not paid 

 attention to these arguments. The thesis pro- 

 pounded by Dr. Cook, that 'individual di- 

 versity persists in spite of uniformity of con- 

 ditions,' '^ may be met by the antithesis : if 

 the environment remains uniform, perfect 

 uniformity of individuals will results'' But 

 since it is practically impossible that any two 

 individuals grow up under precisely the same 

 conditions, a diversity of individuals results. 

 This is a fundamental law. It is, however, 

 not an innate, inexplicable quality of organ- 

 isms, but is due to the external conditions, 

 which continuously are changing and varying, 



^^ Pr. Amer. Phil. Soc, I. c. 



" Pfeffer, ' Die Umwandlung der Arten, etc.,' in 

 Verh. Naturw. Ver. Hamburg (3), 1, 1894. 



" Science, I. c, p. 669. 



^^ Biol. Centralbl., I. c, p. 153. Science, June 

 .22, 1906, p. 951. 



" Science, I. c, p. 306. 



" See Davenport, in Science, November 25, 

 1904, p. 704: 'Two individuals of the same family 

 develop alike only under the same conditions of 

 environment.' See also Copeland, in Bot. Qaz., 

 3S, 1904, p. 426. 



