Effects of Environment 345 



And evidently the apparent persistence of certain ancient 

 simple forms shows, and is accounted for, in a persistence 

 (or at least the very slow change) of their environment; 

 and at the same time their flexibility under change, shows 

 that there may have been many broods and families of their 

 output, led away from the old stock and evolved into related 

 forms, in new environments in which they in turn became 

 settled, when the new environment became, and remained, 

 settled. Thus there are logical reasons for approximate 

 constancy of type as well as for variability of type and there 

 is no denial of evolutionary change to be found in the fact 

 that some species do not change. Environment influences 

 heredity either for steadfastness or for change. 



