DEPARTMENT OF EXPERIMENTAL EVOLUTION. 91 



Inheritance of Human Skin-color. — As an apparent case of blending, the 

 inheritance of skin-color in crosses between whites and negroes has com- 

 manded much attention. With the aim of extending studies published some 

 years ago, a field worker of the Eugenics Record Office was sent to Ber- 

 muda to collect data ; and later the Director of this Department visited Ja- 

 maica and secured cooperation for studies upon some 80 families. All de- 

 terminations of skin-color are made quantitatively by means of the "color- 

 mixer." Altogether data on over 125 families have been secured, with clear 

 evidence that the skin-color of negroes depends upon two gametic factors 

 for black pigment. This conclusion immediately explains all of the observed 

 gradations of skin pigment in "colored" persons of all grades ; demonstrates 

 that wholly white-skinned persons may arise even in the second generation 

 from negro parents, and proves that skin-color is no exception to the law of 

 segregation of determiners in the germ-cells. 



STUDIES ON TERATOLOGICAL VARIATIONS. 



Teratological conditions are relatively so rare that there have been few 

 studies made upon the laws of their occurrence, degree of development, and 

 inheritance. Dr. Harris is dealing with large numbers for such studies. 

 He has examined about 500,000 seedling beans and nearly 200,000 fruits of 

 PassMora. The abnormalities found are being studied and analyzed. 



QUANTITATIVE STUDIES OF SELECTIVE ELIMINATION. 



Material progress in this subject has been made by Dr. Harris, working 

 with various flowering plants. Working with the physiological characters 

 of fertility, fecundity, and seed-weight, and asymmetry, he has used them 

 to study unfitness for survival. He finds that small and large seeds have 

 about the same chance of developing to maturity in the field, but in neither 

 case is the chance so good as for the seeds of more intermediate weight. 

 He sought an answer to the question : Have abnormally shaped seedlings 

 an equal chance of developing to maturity with normals? This involved 

 the examination of over 200,000 seedlings and the planting of 5,030 normals 

 and 4,217 abnormals. The answer was : There is a relatively high elimination 

 of the abnormals. In further studies it is hoped to test the relative elimi- 

 nation of each type of abnormality. 



INFLUENCE OF STARVATION OF PARENTS UPON CHARACTERISTICS OF PROGENY. 



Dr. Harris has published in the June (1912) number of the American 

 Naturalist a first study on this subject, based on many thousands of bean 

 plants. Beginning with very similar seeds, of as nearly as possible similar 

 potentialities, he planted some in poor soil and others in good soil; gathered 

 the seed from the two lots, and, the next year, planted them side by side in a 

 different, fairly fertile field. In another set of experiments two generations 



