REVIEWS OE BOOKS. 



295 



appears to know nothing of ecology, or the present-day method of 

 teaching botany in the field, as well as in the laboratory, which should 

 always have the former as its sole aim and object. 



"The Principles of Heredity." By G. Archdall Reid, M.B., F.R.S.E. 

 Second edition. 8vo. 379 pp. (Chapman & Hall, London.) 12s. Qd. 

 net. 



The author of this work maintains that variations, with very rare 

 exceptions, are spontaneous ; in other words, he insists that offspring 

 difi'er inherently from their parents quite independently of the action of 

 the environment. He supposes that the germinal cell-descendants of the 

 fertilised ovum vary amongst themselves for precisely the same reason as 

 the somatic descendants vary when some become skin, others bone, and 

 others muscle-cells. He points out that, though the germ-cells from 

 which spring a litter of puppies, kittens, or pigs have all existed under 

 practically identical conditions, yet the members of the litter may, and 

 indeed always do, vary greatly in all sorts of different directions. More- 

 over, from time immemorial many human races have been exposed to 

 diseases which literally soak the germ-cells in virulent toxins; thus 

 Negroes on the West Coast of Africa have suffered for hundreds of 

 generations from malaria. If the action of the environment were the 

 cause of variations, then presumably the toxins should injure the germ- 

 plasm and cause deterioration of the race. But no such result follows ; 

 on the contrary, every human race is resistant to every disease precisely in 

 proportion to its past sufferings from it. It undergoes progression, not 

 deterioration. Thus Negroes, a fine race physically, are very resistant to 

 malaria and Englishmen to consumption, whereas Polynesians who have 

 suffered from neither are very susceptible to both when exposed to 

 infection. We are driven therefore to the conclusion that variations are 

 spontaneous, that they tend to occur all round the specific mean like 

 bullet-marks round a bull's-eye, and that thus are provided the materials 

 for natural selection. If variations were not spontaneous the race would 

 drift helplessly to destruction ; for natural selection would have no scope 

 when variations are all in one direction. 



The author maintains that the study of disease is a very valuable 

 means of investigating the problems of heredity. Every disease supplies 

 us with an enormous series of experiments - which have already been 

 statistically tabulated. Moreover, we are able to eliminate errors of 

 observation and reasoning by comparing, not only individuals, but races. 

 Our knowledge of human beings is more intimate and minute than our 

 knowledge of lower animals and plants ; our observations, therefore, are 

 more accurate and extensive. Disease is the only form of selection to 

 which civilised races are now exposed, other forms of death being rare 

 and non-selective. He discusses the influence of diseases on the fortunes 

 of human races. The capacity for becoming civilised is physical not 

 mental, and depends on ability to resist the infective diseases which 

 prevail when human beings are crowded together. All, or almost all, 

 infective diseases originated by the evolution of saphrophytic microbes 

 into pa.rasitic forms in the long and densely populated centres of the 

 eastern hemisphere, the inhabitants of which, under conditions that 



