THE STUDY OF NATURAL SELECTION 141 



tural characteristics of seedlings in their relation to survival are at 

 hand for garden beans, Phaseolus vulgaris. 37 From a lot of about 238,- 

 000 seedlings germinated in the greenhouse in sand, somewhat over 

 9,000 abnormal and normal plantlets were transferred to the field under 

 as nearly as possible identical conditions. The diagram shows most 

 clearly that the death rate, though very low, is unquestionably selective. 

 Solid dots and lines represent the mortality of the atypical individuals 

 in sixteen arbitrary but logical classes. 38 The actual numbers of deaths 

 in these classes is not large. The death rates consequently fluctuate 

 widely. Yet in every case but one the mortality of the atypical is 

 higher than that of the typical individuals. The solid bar gives the 

 rate for all atypical seedlings while the broken line smoothes the circles 

 connected by broken lines in the same way. 



Seedlings are thrown only into two classes, typical and atypical. 

 The latter is highly heterogeneous, comprising a very wide range of 

 structural variations. Possibly some of these are more fit for survival 

 than are the normal individuals, while others are far less so. Only the 

 collection of far wider series of data will settle the question. On an 

 average the variations from type are clearly inferior. This is precisely 

 the condition which one would expect if natural selection has been a 

 factor of weight in the development of the structural characteristics of 

 the seedling, for the most fit type would be the one preserved. 



It is important to remember that this selective mortality is found 

 in seedlings germinated under as favorable conditions of substratum 

 and temperature as we could give them, and then transplanted to fairly 

 good garden conditions. In nature, a considerable part of the seedling 

 death rate doubtless occurs in the early stages of germination where 

 the nascent root and shoot are subjected to a substratum far less favor- 

 able to growth than those of the seed pan. Again, the transplanted 

 seedlings were practically free from the inter-specific and intra-specific 

 competition which must be intense in nature. The detection of a con- 

 spicuous selective death rate under such optimum conditions can leave 

 little doubt as to the force of natural selection under the severe condi- 

 tions in which plants grow in nature. 



Pigmentation in Man in Relation to Selection. 39 — The problem of 



87 J. Arthur Harris, ' ' A Simple Demonstration of the Action of Natural 

 Selection," Science, N. S., 36: 714-715, 1912. 



88 These comprise about ten "pure lines" each. The fact that the mortality 

 of normals and abnormals tends to rise or fall together has no necessary signifi- 

 cance for heredity. It is probably due, largely at least, to the fact that the two 

 kinds of seedlings were under the same environmental conditions. 



88 So nearly all the work on pigmentation which falls in the scope of this 

 paper has been done on man that a more general heading seems unnecessary. 

 About the only other case for mammals is that suggested by the anomalous 

 behavior of yellow in breeding experiments with mice. The problem has been 



