Mabch 16, 1906.] 



SCIENCE. 



433 



Dr. William Popper delivered a lecture on 

 ' Superstitions of the Arabs,' based on his re- 

 searches and personal experiences among the 

 Arabic-speaking peoples of the Orient. 



One hundred and thirty-five persons at- 

 tended the meeting. A. L. Kroeber, 



Secretary. 



THE BERKELEY FOLK-LORE CLUB. 



The third regular meeting of the Berkeley 

 Folk-Lore Club during 1905-6 was held in the 

 Faculty Club of the University of California 

 on Wednesday evening, January 31. Presi- 

 dent A. P. Lange presided, Professor W. P. 

 Bade acting as secretary pro tern. Dr. W. 

 Popper and Dr. A. W. Ryder were proposed 

 for membership in the club and unanimously 

 elected. Professor G. R. Noyes presented the 

 paper of the evening on ' Servian Heroic Bal- 

 lads.' Mr. Nikolitzsch, who was present as 

 the guest of the club, read one of the ballads 

 in the original. The paper was discussed at 

 length by the members. 



A. L. Kroeber, 



Secretary. 



DISCUSSION AND CORRESPONDENCE. 



ISOLATION AND THE EVOLUTION OP SPECIES. 



I HAVE read with the greatest interest the 

 discussion on isolation and its relation to 

 evolution, commencing with President Jor- 

 dan's article in Science for November 3, 1905. 



There are many reasons for believing that 

 in the earlier stages of the segregation that 

 produces two or more species from one, geo- 

 graphical isolation, or at least some degree of 

 local isolation, has had in many cases an influ- 

 ential part. It is, however, important to ob- 

 serve that, when the local variety multiplies 

 and passes over into areas occupied by the 

 original stock, its continued separate evolu- 

 tion must depend on some other form of iso- 

 lation. 



One form of isolation that may prevent the 

 variety from being swamped by free crossing 

 is seasonal isolation due to its having gained 

 a separate season for propagating. This form 

 of isolation is mentioned in one of the quota- 

 tions given in President Jordan's article.^ 



' See page 552. 



Another form of isolation is what Romanes 

 has called physiological isolation, which he 

 defines as the prevention of free crossing due 

 to physiological incompatibility between the 

 reproductive cells of different groups of crea- 

 tures.'^ 



But this extended use of the word isolation 

 is not found in the works of Darwin, and even 

 at the present time many writers follow his 

 usage by treating the term as meaning the pre- 

 vention of free crossing due to geographical 

 separation. This limited meaning of the word, 

 as used by Darwin and the writers of his time, 

 led me for many years to seek other terms 

 when discussing the broad problem of the 

 prevention of free crossing. Separation and 

 segregation are the terms I have chiefly used.' 



I observe that E. A. Ortmann in his dis- 

 cussion entitled, ' Isolation as One of the 

 Factors of Evolution,' appearing in Science 

 for January 12, 1906, also uses ' separation ' 

 as an equivalent for isolation when meaning 

 - the prevention of free crossing. In some of 

 the previous discussions on the subject it has 

 been pointed out that sometimes the nearest 

 allies of a species are found in the same dis- 

 trict. In such cases the point of chief in- 

 terest is that some other form of separation 

 will be found to prevent free crossing between 

 the different races and species. Closely allied 

 plants may bloom at separate seasons and so 

 occupy the same district without crossing. In 

 other cases the pollen of each variety may be 

 prepotent on the stigmas of the same variety. 

 Varieties of birds and mammals differing 

 chiefly in color may be held apart by sexual 

 or social instincts. These and many other 

 forms of isolation have been pointed out in 

 my work on ' Evolution, Racial and Hab- 

 itudinal,' published by the Carnegie Insti- 

 tution. 



I have also brought together many reasons 

 for believing that without isolation one spe- 

 cies can not be transformed into two or more 



- See ' Darwin and After Darwin,' Part III., 

 entitled ' Isolation,' pp. 43-47. 



' See my three papers published in the Linnean 

 Society's Journal, between 1872 and 1889, also 

 three articles published in the Amer. Jour, of 

 Science for 1890, 



