506 THE AMERICAN NATURALIST [Vol. LVI 



It must not be inferred that this study is an attempt 

 to determine ' ' how far the zygote of an individual de- 

 termines his performance " or " what is the resemblance 

 between the zygotes of two brothers." It is primarily 

 a statistical measurement of resemblance in performance 

 with particular reference to performance in science. 

 With the results of these measurements at hand, some- 

 thing about the resemblances of the zygotes of near rela- 

 tives and about how far the zygote of an individual de- 

 termines his performance may be estimated. 



By resemblance is meant, not identity, but degree of 

 similarity. Gralton, with the idea of particulate inherit- 

 ance in mind, early insisted on measuring resemblances 

 as deviations from an average. He justly claims to have 

 been the first to introduce the law of deviations from 

 the average into the discussions on heredity. ' ' ^ Almost 

 forty years later he is found insisting that "proba- 

 bility is the foundation of eugenics. " * It is here that the 

 statistical method avoids the pitfalls of proof by anec- 

 dote. Given a group, selected for some particular sort 

 of performance, the number in any particular degree of 

 relationship showing similar performance may be de- 

 termined and compared with a similar group of the gen- 

 erality. This is the method used in this study. 



The group studied consists of approximately 1,000 

 American men of science and their families. The wives 

 and the near relatives of the wives of the men of science 

 are included in the data, and the results of the compari- 

 sons offer perhaps the most unique contribution of the 

 investigation. The statistical data include only relatives 

 of a d(\£iToo no more remote than first cousin. These rela- 

 ti\('< nrc: hmtlicrs and sisters, sons and daughters, 

 filth. fs and imithers, nieces and nephews, uncles and 

 aunts, «;r:in(li)ar("nts and first cousins. 



It may be well here to anticipate a criticism of the use 

 of the term resemblance. Since the group of men of sci- 

 ence is made up of persons of known distinction and since 



3 " Hereditary Genius," Preface, 1869. 



4 Spencer lecture, 1907. 



