xx THE INFLUENCE OF ENVIRONMENT 401 



mission of somatic modifications (badly called " the 

 inheritance of acquired characters ") may be stated thus : 

 Does a structural or metabolic change directly induced 

 in the body of an individual organism as the result of 

 some peculiarity in function (use and disuse) or in environ- 

 ment and nurture generally, ever affect the germ-plasm 

 in the reproductive organs in such a specific or repre- 

 sentative way that the offspring will thereby, though not 

 subjected to the nurtural peculiarity in question, exhibit 

 the same modification that the parent acquired, or even 

 an approximation towards it ? 



It is easy to interpret evolutionary change on the 

 Lamarckian assumption that somatic modifications are 

 transmissible, but it is difficult to find any convincing 

 evidence for the assumption. It is admitted that somatic 

 modifications may have secondary effects on the germ- 

 cells and on the offspring (especially in the case of the 

 viviparous mammals), but that is not proving the trans- 

 missibility of particular modifications. It is probable that 

 long-continued, deeply saturating environmental and 

 functional peculiarities may produce substances that 

 enter into the cytoplasm of the germ-cell or into the 

 embryonic body (e.g. the mammalian foetus or the seed 

 of a flowering plant), but there is as yet no convincing 

 evidence that the resulting changes grip the constitution 

 permanently. It is not impossible that particular modifi- 

 cations of an incisive sort may liberate very specific 

 chemical substances, like hormones, and that these may 

 be carried to the germ-cells and accumulate there with 

 subsequent formative (morphogenetic) influence, but 

 facts are required to substantiate this hypothesis. As to 

 diseases, so often referred to in this connection, ' when 

 we come to understand that pre-natal infection is not 

 inheritance, that inheritance of a predisposition to a 

 disease is not inheritance of the disease, that the general 

 weakening of the offspring through disease in the parent 

 is a very different matter from the transmission of a 

 specific disease, we are almost irresistibly led to the con- 

 clusion that in the sense in which the word " inherited ' 

 is used in biology there are no inherited diseases. What 



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