362 THE AMEBIC AN NATURALIST [Vol. LI 



now temperate, on the basis of processes now going on in 

 certain parts of the earth; and just as the astronomer 

 creates the planetary systems in his mind by forces that 

 still govern, so the biologist mnst conceive evolution in 

 the past to have been the result of agencies that are still 

 causing change to-day. Whatever causes evolution now 

 may conceivably have caused it during tlie early history 

 of living things, and tlicie arc no ciicniiistaiices which 

 compel one to devise otiicr caiix'- Tor pa>t cliaiige. 



Adherence to this principle automatically removes the 

 first solution of the problem of the method of evolution 

 from the realm of the investigator who deals only with 

 past events or the results of past occurrences, and places 

 it in the hands of him who studies present-day phe- 

 nomena. Conclusions based on statistics have repeatedly 

 shown how dangerous it is to argue from end results to 

 causes. The compiler who finds that among the poorer 

 classes of a population the ratio of male children to female 

 is higher than in the well-to-do classes, and concludes that 

 deficient nutrition causes the high male-production, might 

 also have discovered, had his investigations borne upon 

 that point, that the poorer classes lived in houses pro- 

 tected with a cheaper grade of paint or even without this 

 protection. It would have been ridiculous to conclude 

 that cheap paint favoi-ed boys, liut that conclusion would 

 have been as ]icarl\ innm/ })y tlic data collected as was 

 the more plau.-il.lc conclusion involvi no- nutrition. Causes 

 are not safely to he judged from results. In discovering 

 the method of evolution, the initiative is denied the paleon- 

 tologist, zoogeographer and the morphologist. No doc- 

 trine of scientific cloture is here advocated, however, for 

 the right of debate and even of veto is still theirs. The 

 experimentalist alone may propose, but his colleagues 

 employing the older forms of investigation may, and 

 doubtless will, dispose. The experimentalist accepts his 

 burden cheerfully. He knows that he may be unable to 

 create a correct theory, but he prefers dispensing with a 

 theory to adopting the wrong one. 



