HEREDITY 479 



winian days, men always spoke of heredity with a capital 

 letter, as if it were a power that did things, as many people 

 still talk of Evolution, but one of Darwin's many services 

 was that he showed the linkage between generations to be 

 amenable to scientific experiment and description. 



In mankind one generation may influence its successors 

 by tradition and institutions, by literature and art, and in 

 similar ways which are outside heredity in the biological 

 sense. For the extra-organismal legacies the term social 

 heritage may be usefully restricted, — a usage which would 

 leave Galton's term natural inheritance for all that is handed 

 on by means of the germ-cells, namely the egg-cell and the 

 sperm-cell. The natural inheritance includes all that the 

 organism is or has to start with in virtue of its hereditary 

 relation to parents and ancestors. 



In most mammals, where the unborn offspring is carried 

 by the mother for a more or less prolonged period — the two 

 being bound together in a very intimate ante-natal partner- 

 ship or symbiosis — the natural inheritance of the ofi'spring 

 may be influenced by peculiarities in the available maternal 

 nurture. The same is true in all cases where the parents, 

 plants as well as animals, nurture the ofi^spring. It is plain, 

 though often forgotten, that ante-natal dints or imprints are 

 not in the strict sense part of the natural inheritance. The 

 word nurture, which Galton raised to the rank of a technical 

 term, includes all manner of extrinsic influences, environ- 

 mental, nutritional, and functional, which play upon the 

 organism, or with which the organism plays. Modifications, 

 as we have seen, are structural changes in the body of the 

 organism directly induced in the individual lifetime by 

 peculiarities in function or environment (including food, 

 etc.), which transcend the limit of organic elasticity and 



