THE LIMITS OF HEREDITY i <S9 



The records of similar twins show that ilhicsses 

 clearly retard i^rowth, and may thus cause permanent 

 differences between twins. Some inherited differences 

 also first develop late in life. 



The number of the Journal of Heredity for December, 

 1 91 9, is devoted entirely to twins, and contains 

 thirty figures, chiefly photographs of twins, which 

 show remarkable degrees of resemblance. One ]jair 

 of grown-up brothers have not only identical features, 

 but the same height and weight, the same tastes, 

 disposition, and talent. Another pair of identical 

 twins of exceptional abilit}" have never differed 

 more than a pound in weight, never varied more 

 than o-i per cent, in their college marks, and although 

 absolutely dependent upon glasses, can wear each 

 other's. Their illnesses have often coincided, and 

 most of their tastes are similar. But their tailor says 

 that one of the twins has a short left arm and the 

 other a short right arm — a mirror-image difference 

 such as frequently occurs in twins. Several pairs of 

 these twins are illustrated in Figs. 30 to 35. 



The record of identity in another case extends to 

 size, voice, and tastes in music, but they differ in 

 their taste for mathematics. Twins which were 

 separated at three years of age (Fig. 34), and have 

 since remained apart, show^ an equall}' striking 

 identity of features. The handwriting, which is 

 known to be an index of character, is closely alike 

 in many twins, in one case " virtually identical," 

 but differences are also recorded. 



There are clearly differences in the degree of 

 resemblance between *' identical " twins. One pair 

 of men twins agree in features and in their likes and 

 dislikes, diversions, foods, and intellectual interests. 

 They both suffer from night-blindness, but their hand- 

 writing is " very different." Another pair have 

 similar tastes for poetry and music, and enjoy the 



