The Journal or Heredity 



In the case considered the people 

 generally have been of small stature as 

 far back as their history extends. 

 There has been no substantial change 

 in the average height of the race within 

 historical times. From this we may 

 conclude that the ancestors of the pres- 

 ent generation were mainly of the 

 present normal height; and that only 

 a few of them were much taller or 

 shorter than this. 



The above diagram, then, represents 

 substantially the relative proportions 

 of the three classes at each successive 

 generation of the population. It ty]ji- 

 fies the future distribution, as well as 

 the past, unless some means can be 

 found to change it. 



The desirable and undesirable classes, 

 like the normal, arc sprung mainh- 

 from normal parents; so that it 

 is obvious that no process of inter- 

 ference with the marriages of these 

 classes could much affect the relative 

 proportions of the three classes in the 

 next generation of the community. If, 

 for example, the desirables and unde- 

 sirables should all decide to lead celibate 

 lives so as to leave no descendants, we 

 would have just about as large a pro- 

 portion of desirables and undesirables 

 in the next generation of the commun- 

 ity, born from the normal class. 



SELECTION IN MARRIAGE. 



The individuals belonging to the 

 desirable and undesirable classes are 

 not only few in number, but are scat- 

 tered throughout the community. They 

 appear only here and there as excep- 

 tional cases, and are not segregated 

 from the others in their actual distri- 

 bution in the poijulation. If, then, 

 they decide to marry, it is obvious that 

 most of the desirable and undesirable 

 individuals will marry normal i^ersons, 

 because normal i3eo]jle constitute the 

 bulk of the community with whom they 

 come in contact; and the offspring will 

 tend to revert to the normal type of 

 the race. From this it follows that, on 

 the whole, the oflfs])ring of the desirables 

 will Vie less desirable than themselves; 

 and the ofFsjjring of the undesirables 



more desirable; most of the oflfspring 

 will be of the normal type. 



Given a large normal class, and two 

 small classes,' the desirable and unde- 

 sirable, the i)roblem is. how to increase 

 the ]:»ro]jortion of desirable children 

 born from the normal population. 



This can be accomplished by mar- 

 riage with members of the desirable 

 class. 



In the ty]jical case considered, this 

 would mean that ])ersons of normal 

 height would increase their liability to 

 have tall children by marrying tall 

 people. 



Where normals marry normals a small 



proportion (say 1%) of the offspring will 



belong to the desirable class. 



Where normals marry desirables the 



percentage of desirable offspring will be 



increased (say to IC^^c). 



Of course, it is only possible for a 

 small proportion of the normal popula- 

 tion to marry persons belonging to the 

 desirable class, on account of limited 

 numbers. The range of choice, how- 

 ever, may be extended by marriages 

 with brothers or sisters or close blood 

 relatives of desirable persons. That is 

 upon the asstimption that we are here 

 dealing with an inherited character- 

 istic. 



PROOF OF INHERITANCE. 



The late Professor W. K. Brooks, of 

 Johns Hopkins Universit>', said :' 



"An inherited characteristic may, or 

 may not, have been manifested by the 

 parents or other ancestors. ... If 

 it is more common either among the 

 ancestors or the brothers and sisters and 

 cousins of the organism than it is in the 

 race at large, this fact is scientific proof 

 that it is an inherited characteristic." 



Where a ])ectiliarity manifests itself 

 in only one memlicr of a family we arc 

 dealing with a sjjoradic case; and the 

 peculiarity may, or may not, be trans- 

 mitted to the descendants: But where 

 a number of people in the same family 

 exhibit the same congenital i)eculiarity 

 we have good reason to believe that it 



' See appendix to Rt-p. Rova! Comm. on Blind, Deaf and Dumb, etc., London, 1889, ii, 

 322: also Education of Deaf (Miildnn, Pt. II, p. 104, Volta Bureau. Washington, D. C, 1892. 



