678 REPORT— 1903. 



' variations ' in weight. Now, such variations may be due partly to differences in 

 the muscular training, the nourishment, the general health, and other post-natal 

 causes ; but it is assumed, and there are doubtless good reasons for the assumption, 

 that if all these post-natal influences had been equal throughout life there would 

 still remain variations in weight of lesser amplitude than is usual, but nevertheless 

 substantial. 



The variation of the adult in weight, therefore, is a compound quantity, partly 

 due to the influence of external conditions upon the growing body, and partly due 

 to a quality or character present at birth .ind usually supposed to be inherited 

 with the germ-plasm from one or both parents. The former may be called the 

 artificial part of the variation, or for brevity the artificial variation, and the latter 

 the natural or inherited variation. In the character of weight in human beings 

 there can be no doubt that artificial variation is predominant, the character being 

 a very fluctuating one and liable to profound modification in the varying vicissi- 

 tudes of civilised human life. 



In the character of stature the artificial variation is probably much less pre- 

 dominant. The children of tall parents grow into tall men and women, however 

 handicapped in early life by ill-health or insufficient nourishment, and the children 

 of short parents remain short in adult life, however healthy and well fed in their 

 youth. Nevertheless, he would be a bold man who would assert that the character 

 of stature is uninfluenced by the environment, and that the short people would not 

 have been taller had the conditions of their life in childhood been more favourable, 

 or the tall people shorter if the conditions in their early life had been less 

 favourable. 



Finally, we have, in the colour of the iris, the shape of the ear, and the size of 

 the teeth, characters which are usually considered to be unmodified by post-natal 

 conditions, or at least so slightly modified by them that the differences observed 

 in them may be regarded as almost pure natural variations. Now, if we turn our 

 attention to characters such as weight, which we feel certain are influenced very 

 profoundly by the environment, we might be tempted to exaggerate the import- 

 ance of the environment in moulding or forming the characteristic features of the 

 adult organism, as, in the opinion of many authorities, Lamarck did, and many of 

 his followers are still doing. U, on the other hand, we confine our attention to 

 sucli characters as the colour of the iris or the shape of the ear, we might be 

 tempted to under-estimate the influence of the environment. 



This brings us to the important question whether the characters of the adult 

 that are due to the influence of the environment, and tbat part or degree of any 

 character which is more or less modified by the conditions of the earlier stages of 

 life are or are not transmitted by parents to their offspring. Time will not permit 

 me to discuss this difficult problem here. Rightly or wrongly, I agree with those 

 who maintain that acquired characters are not inherited, and' I intend to assume 

 for the purpose of the argument that follows that they are not inherited. I wijl 

 also assume, and I must say that the facts seem to be conclusive in favour of this 

 assumption, that the characters which are usually supposed not to be influenced, 

 or to be only slightly influenced by, the environm'ent are capable of transmission by 

 heredity. 



We have, then, in most variations a part that can be transmitted and a part 

 that cannot be transmitted by heredity from parents to offspring, and we find in 

 every plant and animal an enormous difference in the proportions of these two 

 parts in different organs. _ It is not difficult to see the general reasons for these 

 differences. It is clearly important that some organs should be plastic— i.e. capable 

 of changing in form and size to meet the varying changes in the environment, and 

 that others should remain relatively constant in spite of changes in the environ- 

 ment. Thus the shape .and size of the branches of an oak in a plantation will vary 

 enormously, according to the light and space they have for their development, 

 whereas the anthers, the pistils and fruit, will be relatively constant in form and 

 colour. It is clearly important for a chamieleon that the colour of its skin should 

 vary according to the colour of its environment ; but it is none the less important 

 that the shape and muscular organisation of its tongue should remain relatively 

 constant throughout life. 



