CHAPTER IV 



THE INHERITED EFFECTS OF CHANGES INDUCED BY 

 EXTERNAL FACTORS 



IT has been pointed out that in butterflies the changes brought 

 about by higher and lower temperatures give rise to forms that 

 resemble southern and northern varieties of the same butter- 

 flies. The question at once arises whether species may not 

 have originated in this way. 



Fischer found that when a dark moth, produced by cold, 

 was paired with another similar moth, the offsprings were also 

 dark. His experiments extended, however, only to the first 

 generation, and consequently the cold may have acted directly 

 on the germ-cells of the parents. Highly important as this 

 observation is in showing that the undeveloped germ-cells may 

 be affected in the same way as the somatic tissues of the pupa, 

 so that even under altered conditions the effect persists, yet the 

 result as it stands does not conclusively show that permanent 

 racial or specific changes have been produced in this way. 

 Were such forms bred for several generations at a warmer 

 temperature, it is possible that they would return again to their 

 original condition. The new type might persist only so long as, 

 or a little longer than, the external conditions are the same as 

 those that produced it. The change may represent only an 

 extreme fluctuating variation that has been caused by an ex- 

 ternal factor. The results do not appear, from this point of 

 view, to belong to the kind of changes by which new species 

 are made. Nevertheless the question still remains an open 

 one as to whether changed external conditions may not at 

 times cause more permanent effects. Some observations of 

 Standfuss seem to show that such may be the case, although 



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