108 



The Journal of Heredity 



affected by their environment than the 

 brains of dogs and cats, of worms and 

 mollusks. Not only in the heredity- 

 environment complex are there sure 

 to be grt'at differences between higher 

 and lower ty])es in their reactions to their 

 surroundings, Vjut if we have also the 

 problem of free-will to deal with — and 

 we certainly do have it to deal with and 

 perhaps it will be one of the last and 

 most scientific problems of all — then, 

 it is not i:)resuraptuous to suppose 

 that free-will acts somewhat more in a 

 man than it does in a tree. At any rate, 

 if there is any such thing demonstrable, 

 there will be differences and these 

 differences will be measvirable. 



A PROBLEM OF DIFFERENCES 



And this brings us back to the crux 

 of the whole question. The heredity- 

 environment tangle can never be tm- 

 ravelled until it is made into a problem 

 of differences and as far as mental and 

 moral heredity is concerned, there have 

 been very few pieces of evidence found 

 that can be called significant in this 

 respect. But these few are very sig- 

 nificant up to a point, as I shall show 

 later. 



To explain the method of differences 

 it is best to take a single example. A 

 factory manager wishes to test an 

 "efficiency scheme." He keeps all the 

 conditions as nearly as possible the 

 same, introduces his novel method, 

 and if a notable result follows he is 

 justified in ascribing it to the new 

 scheme, or at least he has a probability 

 in his favor, and if he experimented long 

 enough he might ajJi^roach practical 

 certainty. vSuch an experiment would 

 not solve the heredity-environment 

 problem, but it would be a very real 

 contribution, though a very minor one. 

 What it would show would be just 

 what influence one particular change 

 in the environment would V)e likely to 

 have on f)ne jjarticular tyjje or class of 

 men. There would be every reason to 

 supi)Ose that in other manufacturing 

 plants, with about the same sort of 

 workmen, about the same sort of 

 result would be obtained. 



All this throws no light on heredity 

 in worms and fishes, hut for man it docs 



throw clear light as far as it goes; it 

 gives a valuable and definite answer. 

 It is of a type that I believe researches 

 must be if they are best to contrib- 

 ute to the solution of the heredity- 

 environment problem. One of the two 

 factors must be kept virtually .stable 

 or unchanging during the experiment, 

 while the other is observed to 

 change. Many experiments along such 

 lines are beiiig performed all the 

 time at agricultural stations; for ex- 

 ample, the soil is fertilized in sev- 

 eral little adjacent plots with dif- 

 ferent sorts of fertilizer, the seed 

 being always samples from the same 

 lot; the measured differences in the 

 results represent the practical value of 

 the differences in the fertilizers. In 

 the same way if the soil, moisture, 

 sunshine and all the conditions that 

 affect growth be kept as constant as 

 possible, the monetary value of different 

 seeds, of different ancestral strains and 

 crossings can be gradually determined. 

 Thus an essentially practical science 

 of the subject is built up, each experi- 

 menter adding .something, provided his 

 experiment has been properly conducted. 



WRONG STATEMENT OF CASE 



It is a waste of time to argue whether 

 for any one individual, heredity or 

 environment is more important. Each 

 is, in a sense, entirely important. Some 

 changes in the environment are more 

 important than others, some even 

 leading to death of the organism. 

 Some changes in the germ are more 

 important than others, as they lead to 

 trivial or fundamental alterations of adult 

 structure, l)ut there is no way that 

 I know of to make the consideration 

 of them an^ylhing more than a verbal 

 quibble except to specify definite par- 

 ticular traits, which for some reason or 

 other seem interesting or significant, 

 and then to measure those traits by 

 what I have si)oken of as the method 

 of differences. 



It is not easy to get good material 

 for psychological inheritance which can 

 be dealt with in this way. Gener- 

 ally when the heredity is different, as 

 for instance among the various social 

 classes, wealth, education and all the 



