486 



NA TURE 



[September 13, 1906 



between fresh and sea water may produce a large 

 jiroportionate increase in resistance. 



Tliere are many other matters of interest that can- 

 not be mentioned in the space available. The parallel 

 drawn between resistance in shallow water and in 

 layers of different densities is most suggestive. The 

 determination of the critical speeds at which the in- 

 fluence of dead-water rapidly diminishes or disappears 

 and the accompanying changes in the wave-pheno- 

 mena are of great interest. On the whole Dr. Ekman 

 is to be congratulated on his work on an obscure 

 problem that has puzzled many persons; Prof. 

 Bjerknes on his prescience in suggesting the solution 

 and his selection of so capable an investigator; and 

 Dr. Nansen on having decided to get to the bottom 

 of the phenomena of " dead-water." It may be hoped 

 that the subject will not be overlooked by other in- 

 vestigators possessing facilities for experiments on a 

 larger scale. VV. H. White. 



SEGREGATION AS A FACTOR IN EVOLUTION. 

 Evolution, Racial and Habitudinal. By Rev. John 

 T. GuHck. Pp. xii 4-269; three plates. (Washing- 

 Ion : Carnegie Institution, 1905.) 



MORE than fifty years ago Mr. Gulick collected 

 snails on the island of Oahu, and was im- 

 pressed and puzzled by the fact that each valley 

 seemed to be inhabited by peculiar forms. " Valleys 

 only a mile apart were occupied by distinct varieties, 

 and often by distinct species." The more facts he 

 .iccumulated the more puzzling did they appear, and a 

 perusal of the " Origin of Species " left his riddle 

 unread. In many cases of divergence diversity of 

 sexual selection cannot be the cause ; in the case of 

 snails this hardly requires proof. In many of the 

 same cases diversity of natural selection cannot be the 

 cause, because in many cases the divergence is not in 

 proportion to the degree of environmental difference, 

 because the divergence is sometimes non-utilitarian, 

 and for other reasons. 



Gradually Mr. Gulick was led to the position, with 

 which his name is honourably and familiarly asso- 

 ciated, that isolation itself, by preventing all chance 

 of crossing with the original stock, may open the 

 way for new habits, for new forms of selection, and, 

 in short, for new species. He believes that no process 

 of natural selection, or of sexual selection, or of any 

 other form of selection, can transform one species 

 into two or more species without the prevention of 

 free crossing between the branches that are thus 

 transformed. " Isolation is an essential factor in the 

 production and maintenance of divergent types." 

 Segregation in particular, i.e., the intergeneration of 

 like with like, with the prevention of crossing be- 

 tween unlike groups, is one of the fundamental 

 factors in the formation, continuance, and control of 

 divergent types. To substantiate and develop this 

 thesis is the aim of the present bulky volume, the 

 full title of which should read, he tells us, " Habitu- 

 dinal and Racial Segregation ; or the origin and 

 intensification of organic types, guided by innovation 

 and tradition acting under segregate association, and 

 NO. 1924, VOL. 74] 



established by variation and lieredity acting under 

 segregate intergeneration "! 



Mr. Gulick distinguishes racial (or aptitudinal) 

 segregation, produced by the intergeneration of indi- 

 viduals with like innate characters, from social (or 

 habitudinal) segregation produced by the association 

 of individuals with like acquired characters, but these 

 two " spheres of evolution " interact. Hereditarily 

 similar forms draw together, and we have " racial 

 segregation"; modificationally similar forms draw 

 together and we have "habitudinal segregation." 

 Each of these is " controlled by two principles." The 

 former is controlled by racial demarcation through 

 isolation, and racial intensification through survival 

 (in its two forms, selection and indiscriminate elimina- 

 tion). The latter is controlled by habitudinal demar- 

 cation through partition, and habitudinal intensification 

 through success (in its two forms, election and indis- 

 criminate failure). " We have, therefore, four main 

 principles cooperating in the production of segregate 

 types, namely, partition, success, isolation, and sur- 

 vival." All this sounds very " wordy," but it need 

 hardly be said that the author illustrates his new 

 distinctions by concrete instances. And, after all, the 

 terms are of less importance than the analysis of th»- 

 modes of segregation which they express. 



Partition (P), acting on acquired characters, pro- 

 duces habitudinal demarcation with initial habitudinal 

 segregation; election (E), acting on acquired char- 

 acters, produces intensified habitudinal segregation ; 

 isolation (I), acting on inherited characters, produces 

 racial demarcation with initial racial segregation ; 

 selection (S), acting on inherited characters, produces 

 intensified racial segregation ; but we must refer the 

 reader to the book to see what is produced when P 

 and E, I and S, P and I, E and S, respectively work 

 together. The interaction of the principles of segre- 

 gation is illustrated, inter alia, by the Tarpon Island 

 cats, quoted from the New Orleans Times-Democrat , 

 which wade freely off the beach, and even swim out 

 to the oyster boats. 



Moreover, as to P, E, I, and S, each lias its reflexive 

 mode, produced by the action of the members of the 

 species upon each other, and its environal mode, deter- 

 mined by the relations between the environment and 

 the species ; also its regressive aspects, caused by the 

 cessation or reversal of the influence that has been 

 ruling ; and its indiscriminate aspects. There may be 

 conjunctional P, E, I, and S; sexual forms of S, E, 

 and I ; social forms of P, E, I, and S. Moreover, 

 under the environal mode of each principle, the rela- 

 tions between the group and its environment may be 

 determined by conditions within the group {endonomic 

 P, E, I, or S), or they may be determined chiefly by 

 conditions lying outside of the group {heteronomic 

 P, E, I, or S), Eleven forms of P, eleven forms of E, 

 fifteen forms of I, and twenty forms of S are duly 

 distinguished and defined, and we begin to feel that 

 the grammar of evolution is not easy. Altogether 

 twenty-one forms of segregation are found in natural 

 species, and to these must be added institutional 

 segregation and eight forms of intensive segregation 

 found to occur in man. 



