354 APPENDIX A 



the plants were now grown in sunshine and under precisely 

 similar conditions. In the fourth year plants with an ex- 

 clusively shady ancestry produced flowers but failed to mature 

 fruit." 1 



Many other examples of racial change under the direct action 

 of the environment have been alleged. 2 Most of them admit of 

 the simple explanation that the reputed variations are no more 

 than mere acquirements. But such examples as those instanced 

 by Pictet and Clayton cannot be set aside so easily. Pictet's 

 observations raise the presumption that under novel conditions 

 the germ-plasm may be affected temporarily by direct action, but 

 that it tends always to swing back to the normal, the change in 

 the offspring being something between a variation and a modifi- 

 cation. Obviously Pictet's observations do not disprove the 

 contention that racial change permanent change that is is not 

 usually due to direct action. The lesson conveyed by Clayton's 

 beans is even more instructive. We do not know that the 

 alteration caused by shade was more permanent, more innate, 

 than that caused by nutrition in Pictet's butterflies, but, in any 

 case, its occurrence rendered the race extinct. Had there been 

 among the beans a single individual, the germ-plasm of which 

 was insusceptible to the direct action of the environment, the 

 descendants of it would have survived, and an insusceptible type 

 would have been established by Natural Selection. This in- 

 susceptibility, therefore, was essential to the persistence of the 

 race, and a like insusceptibility to the influences by which they 

 are surrounded is essential to the persistence of all races ; for 

 all races are exposed to influences injurious to the cells of the 

 individual. 



No doubt germ-cells are as liable to injury as any other kind 

 of cell. But the somatic cells reproduce their types truly even 

 when exposed to prolonged injury, as in the case of a gland 

 affected by tuberculosis. We have no reason to suppose that germ- 

 cells are less resistant. Apparently their hereditary tendencies 

 have been so firmly implanted by Natural Selection that an injury 

 which is sufficiently powerful to change them is usually sufficient 

 to cause the death of the cell. It is probable, in fact, that the 

 action of Natural Selection is more complex than biologists 

 have supposed. As indicated by Darwin, the environment 

 eliminates unfit individuals and so produces evolution; but, in 

 addition, it is likely that it eliminates unfit germ-cells that is, 

 all germ-cells easily altered by its influence. Natural Selection 

 therefore operates, not only on the individuals of a race, but 

 antecedently on the germ-cells whence they spring; and this 

 doubtless is a partial explanation of the fact that even the 



1 Vernon, Variations in Animals and Plants, p. 247. 



2 See for example Evolution and Adaptation, by Prof. H. D. Morgan. 

 Chapter IX. 



