November 25, 1910] 



SCIENCE 



763 



left where Darwin left us, without any clue to 

 the manner in which natural selection is sup- 

 plied with the material on which it may act. 



The biogenetic law reappears in all its pris- 

 tine vigor, indeed with added vigor, for it is 

 held to be inconceivable that the phylogenetic 

 recapitulation should not occur if it be granted 

 that species arose by evolution and that the 

 offspring recapitulates the parental develop- 

 ment. Both progressive and retrogressive 

 modifications of the recapitulation occur, and 

 of these the retrogressive ones tend to be the 

 greater either in frequency or magnitude or 

 in both. Retrogressive modifications are omis- 

 sions from the complete recapitulation and are 

 therefore identical with reversions. The omis- 

 sion may, however, be merely apparent in some 

 cases; an ancestral trait may appear to have 

 been dropped when in reality it is merely 

 latent, and hence the reappearance of a dor- 

 mant ancestral trait is not a reversion. Re- 

 gression in the Galtonian sense is merely the 

 first stage of retrogression. 



The object of sexual reproduction is not the 

 production of variations, since these occur 

 with parthenogenesis; its function is the 

 blending of parental characters. Certain char- 

 acters, however, are alternative and among 

 these are sexual characters, using the term 

 sexual in the widest sense. Thus every indi- 

 vidual possesses three sets of characters, one 

 set common to both sexes, that is to say, patent 

 in both, and two sets of sexual characters, one 

 'of which is patent and the other latent, accord- 

 ing to the sex of the individual. This same 

 condition Dr. Eeid finds in Mendelian inherit- 

 ance, the dominant characters being patent 

 ones and the recessive latent, and he carries 

 the idea a step further in maintaining that 

 instead of sexual characters being Mendelian, 

 these latter characters are sexual, the Men- 

 delian phenomena depending on their relative 

 potency or latency, rather than on the pres- 

 ence or absence of definite determining fac- 

 tors. " Unit segregation, gametic purity and 

 independent inheritance of characters (in the 

 Mendelian sense) are all myths that have been 

 founded on experiment, but have not been 

 tested by it or in any other way " ! 



In discussing mutations, to which class of 

 variations he assigns those characters that 

 show Mendelian phenomena. Dr. Eeid main- 

 tains that " In hardly a single instance has the 

 crossing of natural varieties revealed a latent 

 ancestral character," that is to say, a recessive 

 parental character! But in domestic races 

 this revelation is frequent and therefore nat- 

 ural and artificial selection are essentially 

 unlike. Man in dealing with domestic races 

 uses mutations, but nature uses fluctuating 

 variations. Mutations occur in nature, but 

 " never yet has a mutation been recorded — 

 neither in man, nor in lower animals, nor in 

 plants — that gave its possessors an advantage 

 in the struggle for existence so overpowering 

 that it enabled them to supplant the ancestral 

 type." 



In what has been said the attempt has been 

 made to state concisely Dr. Eeid's position 

 with regard to the principal problems of in- 

 heritance, and the abstract corresponds to 

 about two fifths of the book. The remainder 

 is occupied with discussions of the sociological 

 and psychological applications of the author's 

 conclusions, and concerning these, interesting 

 though they are, space remains but for an 

 illustrative statement and a quotation. The 

 author holds that disease, alcohol and nar- 

 cotics are the only important selective factors 

 in the case of the human species, and the only 

 progressive evolution that human races under- 

 go is that which tends to resistance to these 

 factors. Acquired immunity or total absti- 

 nence will not lead to the development of that 

 resistance, and, far from being for the good of 

 the race, would, if effective, expose it eventu- 

 ally to disaster from the very causes it en- 

 deavored to avoid. A newly introduced dis- 

 ease if fatal, is always more so than one to 

 which the community has been for some time 

 exposed and to which it has, by natural selec- 

 tion, gained some resistance. 



" In considering any practical problem we 

 must first of all determine what we propose to 

 improve — whether germinal potentialities or 

 characters which developed under the stimulus 

 of nutrition, or of use, or of injury — and then 

 consider in what way they may best be im- 



