Wilder: Physical Correspondences 



411 



STRIKING SIMILARITY IX PALM AND 

 SOLE PRINTS 



In several papers during the past 

 twenty years I have put forth as an 

 exact criterion of the degree of bodily 

 correspondence between twins the use 

 of the friction-skin patterns covering 

 the surfaces of the palms and soles ; 

 parts the individual character of which 

 is now well known. Sir Francis Galton 

 and others, notably Fere, have made 

 careful comparisons of the finger-print 

 patterns, with for the most part rather 

 inconclusive results, but in my opinion 

 these areas are too small and the varia- 

 tions too slight to serve well for the 

 purpose. The larger area presented by 

 an entire palm or sole, on the other 

 hand, allows the delineation of a much 

 more extended pattern, or rather a 

 series of patterns, in which the general 

 configuration of the whole surface may 

 show a striking similarity not even no- 

 ticeable in a single detail of the size 

 and importance of a finger-print only. 



The result of the study of some fifty 

 sets of twins in this particular justifies 

 me in making the following claims : 



1. The friction-skin configuration of 

 twins corroborates the conclusions 

 based upon the general physical appear- 

 ance, that there are two distinct types 

 of human twins, duplicate (or identi- 

 cal) and fraternal. Twins of the first 

 type are monochorial at birth, and rep- 

 resent typical cases of polyembryony, 

 similar to the normal condition in 

 armadillos ; those of the second type 

 are dichorial, and represent simply 

 cases of multipary, the normal condi- 

 tion in many small mammals like dogs 

 and rabbits. 



2. Twins of the first type show the 

 high degree of facial and bodily resem- 

 blance noted throughout this magazine 

 and illustrated through photographs ; 

 those of ihe second type either may or 

 may not look alike, as in the case of 

 any brothers or sisters of distinct birth. 

 Twins of the first type are necessarily 

 of the same sex; those of the second 

 may be either of the same or of oppo- 

 site sex, as in any two children of one 

 family. 



3. The correspondence in the fric- 

 tion-skin configuration is confined to the 

 general plan of the surface as a whole 

 and does not extend in the least to the 

 finer details, the "minutiae" of Galton. 

 Thus a loop pattern upon a given area 

 of the right hand of one twin will be 

 found, usually to about the same de- 

 gree of development, in the corre- 

 sponding place on the right hand of 

 the other, but there will be no similar- 

 ity in the number of individual ridges 

 of which the loop is composed in the 

 two cases ; technically, the "ridge- 

 count" in the two cases will be differ- 

 ent. The two will present the same 

 painting, but with diff'erent brush- 

 marks. Heredity determines with con- 

 siderable precision the occurrence and 

 arrangement of patterns and other 

 larger features, but the execution of 

 them, as drawn by the ridges, is wholly 

 individual, and is quite beyond the limit 

 of hereditary control. 



4. Not only does the degree of de- 

 velopment of a given pattern in the 

 two twins differ within considerable 

 limits, but it frequently happens that 

 a definite pattern in one twin may be 

 represented in the other by nothing 

 more than a convergence of lines rep- 

 resenting the last vestige of the pat- 

 tern in question. In such cases, how- 

 ever, there is always a well-marked and 

 definite area left for either the pat- 

 tern or the pattern vestige, thus keep- 

 ing the general plan of the whole area. 



5. In duplicate twins there is, in both 

 hands and feet, a marked correspond- 

 ence between the two sides, so that the 

 right and left hands of each twin cor- 

 respond as completely as do the right 

 or the left hands of the two individuals. 

 All four of the hands involved are thus 

 duplicates of virtually the same pic- 

 ture, and the same phenomenon is 

 shown in the four feet. It is true that 

 in normal single individuals some form 

 of bilateral symmetry between the two 

 sides is often found, but this is seldom 

 as complete as in duplicate twins. There 

 are found also all grades of dissimi- 

 larity between the two sides, while they 

 are often entirely unlike. Then, too, if 



