On the other hand, it must be fairly evident, from the pains which Nature has taken to arrange for the transmission of the germ-plasm from generation to generation, that she would also protect it from injury with meticulous care. It seems hardly reasonable to suppose that a material of this sort should be exposed, in the higher animals at least, to all the vicissitudes of the environment, and to injury or change from the chance of outward circumstances.
In spite of these presumptions which the biologist would, to say the least, consider worthy of careful investigation, the world is full of well-intentioned people who are anxious to improve the race, and who in their attempts to do so, wholly ignore the germ-plasm. They see only the body-plasm. They are devoted to the dogma that if they can change the body (and what is here said of the body applies equally to the mind) in the direction they wish, this change will in some unascertainable way be reproduced in the next generation. They rarely stop to think that man is an animal, or that the science of biology might conceivably have something to say about the means by which his species can be improved; but if they do, they commonly take refuge, deliberately or unconsciously, in the biology of half a century ago, which still believed that these changes of the body could be so impressed on the germ-plasm as to be continued in the following generation.
Such an assumption is made to-day by few who have thoroughly studied the subject. Even those who still believed in what is conventionally called "the inheritance of acquired characteristics" would be quick to repudiate any such application of the doctrine as is commonly made by most of the philanthropists and social workers who are proceeding without seeking the light of biology. But the idea that these modifications are inherited is so widespread among all who have not