The Editor: Nature or Nurture? 



229 



some power to mould the individual, 

 by giviiig his inborn possibilities a 

 chance to express themselves, but that 

 nature says the first and last word. 

 Francis Galton, the father of eugenics, 

 hit on an ingenious and more convincing 

 illustration, by studying the history of 

 twins. 



There are, as you know, two kinds of 

 twins — ordinary twins and the so-called 

 identical twins. Ordinary twins are 

 merely brothers, or sisters, or brother 

 and sister, who happen to be born 

 two at a time, because two ova have 

 developed simultaneously. The fact 

 that they were born at the same time 

 does not make them alike — they differ 

 quite as widely from each other as 

 ordinary brothers and sisters do. Iden- 

 tical twins have their origin in a different 

 phenomenon — they are halves of the 

 same egg, which split in two at a very 

 early stage of its development, each of 

 the halves then developing into a 

 separate individual. As woiild be ex- 

 pected, these identical twins are always 

 of the same sex, and extremely like 

 each other, so that sometimes their own 

 mother can not tell them apart., -This 



"^ /"likeness extends to all sorts of traits— 

 ^ they may lose their milk teeth on the 



J. I same day, they may become sick on the 

 \ same day with the same disease, even 



^ though they be in different cities, and 



' ,so om 



Now Galton reasoned that if environ- 

 ment really changes the inborn char- 

 acter, then these identical twins, who 

 start life as halves of the same whole, 

 ought to become more unlike if they 

 were brought up apart ; and as they grew 

 older and moved into different spheres 

 of activity, they ought to become 

 measurably dissimilar. In the case of 

 ordinary twins, who start dissimilar, 

 they ought to become more alike when 

 brought up in the same family, on the 

 same diet, among the same friends, 

 with the same education. If the course 

 of years shows that identical twins 

 remain as like as ever and ordinary 

 twins as unlike as ever, regardless of 

 changes in conditions, then environ- 

 ment will have failed to demonstrate 

 that it has any great power to modify 

 one's inborn nature. 



With this view, Galton collected the 

 history of eighty pairs of identical twins, 

 thirty-five of which cases were accom- 

 panied by very full details, which showed 

 satisfactorily that the twins were really 

 as nearly identical, in childhood, as one 

 could expect to find. I can not quote 

 his long and interesting descriptions of 

 them; I can only state the conclusion. 

 In the case of these thirty-five pairs 

 who were "closely alike" in both body 

 and mind, during childhood and youth, 

 when they were brought up in the same 

 environment, what changes did their 

 separation into different environments, 

 different walks of life, when they grew 

 up, produce? In many cases the re- 

 semblance of body and mind continued 

 unaltered up to old age, notwithstanding 

 very different conditions of life ; in others 

 a severe disease was sufficient to account 

 for some change noticed. Other dis- 

 similarity that developed, Galton had 

 reason to believe, was due to the develop- 

 ment of inborn characters that appeared 

 late in life. He therefore felt justified 

 in broadly concluding "that the onh' 

 circumstance, within the range of those 

 by which persons of similar conditions 

 of life are affected, that is capable of 

 producing a marked effect on the 

 character of adiilts, is illness or some 

 accident which causes physical infirmity. 

 The twins who closely resembled each 

 other in childhood and early youth, 

 and were reared under not very dis- 

 similar conditions, either grow unlike 

 through the development of natural 

 (that is, inherited) characteristics which 

 had lain dormant at first, or else they 

 continue their lives, keeping time like 

 two watches, hardly to be thrown out 

 of accord except by some physical jar." 



Now let us consider the ordinary 

 twins, who were unlike from the start, 

 and see how far nurture has made 

 them resemble each other. I cannot 

 take time to cite Galton's evidence, 

 which was presented in his usual 

 cautious way. It led him to write: 

 "The impression that all this evidence 

 makes on the mind is one of some wonder 

 whether nurture can do anything at all, 

 beyond giving instruction and profes- 

 tional training." The unlike twins 

 never became any more like, no matter 



