10 ON THE ORIGIN OF SPECIES 



affected by the treatment of the parent prior to the act 

 of conception. These cases anyhow show that variation 

 is not necessarily connected, as some authors have sup- 

 posed, with the act of generation. 



Seedlings from the same fruit, and the young of the 

 same litter, sometimes differ considerably from each 

 other, though both the young and the parents, as Muller 

 has remarked, have apparently been exposed to exactly 

 the same conditions of life ; and this shows how unim- 

 portant the direct effects of the conditions of life are 

 in comparison with the laws of reproduction, of growth, 

 and of inheritance ; for had the action of the conditions 

 been direct, if any of the young had varied, all would 

 probably have varied in the same manner. To judge how 

 much, in the case of any variation, we should attribute 

 to the direct action of heat, moisture, light, food, etc. , 

 is most difficult : my impression is, that with animals 

 such agencies have produced very little direct effect, 

 though apparently more in the case of plants. Under 

 this point of view, Mr. Buckman's recent experiments 

 on plants are extremely valuable. When all or nearly 

 all the individuals exposed to certain conditions are 

 affected in the same way, the change at first appears to 

 be directly due to such conditions ; but in some cases it 

 can be shown that quite opposite conditions produce 

 similar changes of structure. Nevertheless some slight 

 amount of change may, I think, be attributed to the 

 direct action of the conditions of life — as, in some cases, 

 increased size from amount of food, colour from par- 

 ticular kinds of food or from light, and perhaps the 

 thickness of fur from climate. 



Habit also has a decided influence, as in the period 

 of flowering with plants when transported from one 

 climate to another. In animals it has a more marked 

 effect ; for instance, I find in the domestic duck that the 

 bones of the wing weigh less and the bones of the leg 

 more, in proportion to the whole skeleton, than do the 

 same bones in the wild-duck ; and I presume that this 

 change may be safely attributed to the domestic duck 

 flying much less, and walking more, than its wild parent. 



