306 THE TREND OF THE RACE 



families of a given size the first and second born show as a rule a 

 preponderating amount of albinism, criminality and tuberculosis. 

 Mongolian idiocy was found to characterize in a rather striking 

 manner the last born of the family. 



When we investigate the incidence of any quality in regard to 

 order of birth in individual families we are not entirely free from 

 statistical pitfalls, if we start with material segregated in institu- 

 tions. If we take individuals of a certain age, say 20, which are 

 confined in a sanitorium, then if the numbers of families are 

 increasing in the population at large the individual will be more 

 apt to be the eldest of a recent family than the younger member 

 of an old family. This possible source of error was pointed out 

 by Mr. Cobb who says: 



"It has hitherto been assumed that if a person of given age is 

 selected at random from amongst fraternities of a given size then 

 all positions in that fraternity are equally likely. But this is 

 not the case. If the number of births has been increasing he is 

 more likely to be one of the older members of his fraternity, and 

 if the number hasbeen decreasing he is more likely to be a younger 

 member. For while the number of births is increasing there are 

 more children born every year who belong to the first half of their 

 fraternities than who belong to the second half." 



In most countries there are more births per annum than 

 previously and a steady increase in the number of families. But 

 granting that this would give us an apparent increase of the first 

 born of any particular age there is a compensating tendency 

 brought about by the declining birth rate. Along with an in- 

 creasing number of people there has been a reduction of the 

 percentage of the later born owing to the increasing restriction of 

 the size of the family. Consider a random group of 20 year old 

 individuals from families of twelve members. Will not this be 

 more apt to represent the last members of the old families than 

 the first members of families that were started later. Suppose 

 that of the families starting in 1825, one in ten contained a 

 twelfth child, which lived for 60 years. Suppose also that of the 

 families starting in 1875 only one in one hundred had a twelfth 



