1 88 PROBLEMS OF GENETICS 



rences which we now know to be ordinary features of descent 

 under uniform conditions, and the origin of variations which 

 were certainly not caused directly by circumstances at all. In 

 the absence of any factorial analysis, or of any conception of what 

 factorial composition means and implies, no one knew what 

 varieties might be expected from given parents. The appearance 

 of any recessive variety was claimed as a consequence of some 

 treatment which might have been applied to the parents. There 

 was no possible standard of evidence or means of controlling it, 

 and thus the discussion was singularly unfruitful. Before we can 

 tell how the course of descent has departed from the normal, we 

 must know what the normal would have been if we had let alone. 

 We are still far from having such knowledge in adequate measure, 

 but it does now exist in some degree, and we are steadily approach- 

 ing a position from which we shall be able to form fairly sound 

 estimates of the true significance of evidence for or against the 

 proposition that environmental treatment can produce positive 

 disturbances in the physiological course of descent. 



Thus described, the field for consideration is very wide. 

 Though the effects of changed conditions were especially studied 

 in the hope of solving the problem of adaptation by direct ob- 

 servation, that, as all are now agreed, is but a part of a more 

 general question. We must ask not only do changed conditions 

 produce an adaptative response on the part of the offspring, but 

 whether they produce any response on the part of the offspring 

 at all. It is not in doubt that by violent means, such as starvation 

 or poisoning of the reproductive cells, effects of a kind, stunting 

 and deformity for instance, can be made evident, just as similar 

 effects may follow similar treatment during embryonic or larval 

 life. Apart from interferences of this class, are there any that 

 may be reasonably invoked as modifying the course of inher- 

 itance? 



No epitome of the older evidence for the inheritance of 

 adaptative changes is here required. That has often been col- 

 lected, especially by Weismann, who exposed its weaknesses so 

 thoroughly as to carry conviction to most minds, and showed 

 that whether the phenomenon occurs or not, no one can yet prove 



