CHAP, xx SUMMARY AND CONCLUSIONS 



presumably no critic will question, but which ought 

 to be made explicit. If evolution is to mean progress, 

 it must at least imply continuous adjustment to a 

 constant environment. If the environment changes, 

 if there is no continuity in the definition of " fitness," 

 there can be no real progress. Dissatisfied with my 

 dwelling, I build myself a house exactly suited to my 

 personal needs. That is a real improvement. But 

 forthwith I have to accept an appointment in a dif- 

 ferent town, and must sell my new house at a loss 

 for whatever it will fetch. The improvement due 

 to building for myself is forfeited, and turns to the 

 opposite. Now in the far-off past our planet is said 

 to have passed through more than one ice age. Of 

 course so tremendous a change in environmental 

 conditions involved the forfeiting of past progress. 

 The tests were all (however gradually) altered. The 

 last became first and the first last. The unfit were 

 now found fit, while the fit proved unfit. Physiologi- 

 cal capital was fatally depreciated, like machinery 

 thrown out of use by a better invention. Only here 

 there was no better invention. There was no con- 

 tinuous progress. There was discontinuity and a 

 change of conditions. Evolution then will scarcely 

 mean progress unless first it is continuous evolution. 

 But continuity in evolution of species implies con- 

 stancy of environment. No doubt, speaking broadly, 

 we have had such continuity on the earth for a good 

 many aeons. 



Secondly, a difficulty occurs as to those species 

 which seem unchanged from remote geological times. 

 Drummond's Ascent of Man has been the one of our 

 authorities which has told us most about these. 



