378 AisrisruAL eepoet Smithsonian institution, 1915. 



than if the body be starved can the full height be attained, but such 

 influences are not superficial and do not alter the genetic constitution. 

 The factors which the individual receives from his parents and no 

 others are those which he can transmit to his offspring ; and if a fac- 

 tor was received from one parent only, not more than half the oflF- 

 spring, on an average, will inherit it. What is it that has so long pre- 

 vented mankind from discovering such simple facts ? Primarily the 

 circumstance that as man must have two parents it is not possible 

 quite easily to detect the contributions of each. The individual body 

 is a double structure, whereas the germ cells are single. Two germ 

 cells unite to produce each individual body, and the ingredients they 

 respectively contribute interact in ways that leave the ultimate prod- 

 uct a medley in which it is difficult to identify the several ingredients. 

 "VVlien, however, their effects are conspicuous the task is by no means 

 impossible. In part also even physiologists have been blinded by the 

 survival of ancient and obscurantist conceptions of the nature of man 

 by which they were discouraged from the application of any rigorous 

 analysis. Medical literature still abounds with traces of these archa- 

 isms, and, indeed, it is only quite recently that prominent horse 

 breeders have come to see that the dam matters as much as the sire. 

 For them, though vast pecuniary considerations were involved, the 

 old " homunculus " theory was good enough. We were amazed at the 

 notions of genetic phj'^siology which Prof. Baldwin Spencer encount- 

 ered in his wonderful researches among the natives of Central Aus- 

 tralia : but in truth, if we reflect that these problems have engaged the 

 attention of civilized man for ages, the fact that he, with all his 

 powers of recording and deduction, failed to discover any part of the 

 Mendelian system is almost as amazing. The popular notion that any 

 parents can have any kind of children within the racial limits is con- 

 trary to all experience, yet we have gravely entertained such ideas. 

 As I have said elsewhere, the truth might have been found out at any 

 period in the world's history if only pedigrees had been drawn the 

 right way up. If, instead of exhibiting the successive pairs of pro- 

 genitors Avho have contributed to the making of an ultimate indi- 

 vidual, some one had had the idea of setting out the posterity of a 

 single ancestor who possessed a marked feature such as the Hapsburg 

 lip, and showing the transmission of this feature along some of the 

 descending branches and the permanent loss of the feature in col- 

 laterals, the essential truth that heredity can be expressed in terms of 

 presence and absence must have at once become apparent. For the 

 descendant is not, as he appears in the conventional pedigree, a sort of 

 pool into which each tributary ancestral stream has poured some- 

 thing, but rather a conglomerate of ingredient characters taken from 

 his progenitors in such a way that some ingredients are represented 

 and others are omitted. 



