30 HEREDITY IN RELATION TO EUGENICS 



secreted in the iris, in northwestern Europe blue, gray or 

 yellow-bkie eyes are found. It seems probable that, once 

 upon a time, or perhaps at many times, an individual was 

 born without brown pigment in the iris. The offspring of 

 such prospered and spread throughout northwestern Europe 

 and migrated thence to America and Australia (Fig. 8). 

 This defect, lack of eye pigment, has had a wonderful 

 history. By noting its distribution the migrations of peoples 

 can be traced. Thus Gray (1907) has shown that, in Scot- 

 land, pure blue eyes are most abundant in the coal and 

 iron districts. ''This is probably due to the Irish inami- 

 grants, it being well known that blue eyes are very common 

 among the Irish." In the Spey valley of Scotland the dens- 

 ity of pure blue eyes is high — probably owing to the Norse 

 invasion at that point. (Fig. 9). So in our country the 

 pigmentation survey that will some day be made will show 

 a high percentage of blue eyes where the Scandinavians 

 and north Germans have settled. Thus eye color, just 

 because it shows no tendency to blend in heredity, is a most 

 valuable aid in history. 



Our loiowledge of heredity of eye color depends on studies made by 

 Galton, 1899, who noted its alternative nature but otherwise overlooked 

 the true method of its inheritance; more recently, by three studies car- 

 ried on simultaneously and independently and pubUshed by G. C. and 

 C. B. Davenport, in November, 1907; by C. C. Hurst in 1908; and by 

 Holmes and Loomis in December, 1909. Since 1907 the present author has 

 collected additional data. Hurst's data have the advantage of having 

 been collected from personal observation, hence the chance of error due to 

 a diversity of collaborators was eliminated. In the other studies the data 

 were supplied by unprejudiced, if not always critical, recorders. 



Applying the test of the 6 (strictly 5) kinds of unions we 

 get the results shown in Table IV. 



