828 THE POPULAR SCIENCE MONTHLY. 



to resemble one another, time and again, somewhat more closely than 

 a brother and a sister. Furthermore, the two elder children and the 

 two younger will tend to resemble one another more, as a rule, than 

 the eldest resembles the youngest, and for a very sufficient reason, be- 

 cause all the habits and constitution of the two parents are liable to 

 change from time to time, and especially after a long interval of years. 

 Hence it will follow by parity of reasoning that two brothers or two 

 sisters, born twins, will tend to resemble one another on the average 

 far more intimately than do any two other members even of the same 

 family. The rationale of this is clear. They are both the children of 

 the one father and the one mother ; they are both of the same sex ; 

 and they are both born at the same time, and therefore under exactly 

 the same conditions of age, health, habit, and constitution on the part 

 of both parents. 



Here, then, we have a crucial instance by which we may test the 

 physical and psychical correctness of this our general a jjriori prin- 

 ciple. If character results in the way I say it does — if it is a product 

 of the interaction of two independent sets of factors, derived equally 

 on the whole from father and mother — then it will follow that, men- 

 tally and physically, twins will far more closely resemble one another 

 than ordinary brothers and sisters do. Now, does the case of twins 

 bear out in actual fact this debated deductive conclusion ? Common 

 experience tells us that it does, and Mr. Galton has supplemented that 

 fallible and hasty guide by the most rigorous inductive collection of 

 instances. The result of his investigation is simply this, that many 

 twins do actually behave under similar circumstances in almost iden- 

 tical manners, that their characters often come as close to one another 

 as it is possible for the characters of two human beings to come, and 

 that even where the conditions of later life have been extremely differ- 

 ent, the original likeness of type often persists to the very end, in spite 

 of superficial variations in style or habit of living. Some of his stories, 

 carefully verified, are very funny. I will supplement them by two of 

 my own. In one case a couple of twins, men, had a quarrel over a 

 perfectly unimportant matter. They came to very high words, and 

 parted from one another in bad blood. On returning to their rooms — 

 they lived apart — each of them suffered from a fit of remorse, and sat 

 down to write a letter of contrition to the other, to be delivered by 

 the morning post. After writing it one brother read his letter over, 

 and, recalling the cause of quarrel, added at once a long postscript, 

 justifying himself, and reopening the whole question at issue. The 

 other brother posted his note at once, but thinking the matter over 

 quietly, afterward regretted his action again, and supplemented it by 

 a second palinodia, almost unsaying what he had said in the first one. 

 I saw all three letters myself the next morning, and was simply amazed 

 at their absolute sameness of feeling and expression. 



The other story relates to a fact w^hich happened, not to twins, but 



