SOME POSSIBLE BEARINGS
OF
GENETICS ON PATHOLOGY
THOMAS HUNT MORGAN
Professor of Experimental Zoology, Columbia University, New York.
Middleton Goldsmith Lecture delivered before the New
York Pathological Society on February 3, 1922.
PRESS OF
THE NEW ERA PRINTING COMPANY
LANCASTER, PA.
1922
Thomas Hunt Morgan,
Professor Experimental Zoology, Columbia University.
It has been pointed out in derision that modern genetics deals,for the most part, with the inheritance of abnormalities and disordersof various kinds—albinos, brachydactyls, cretins, dwarfs,freaks, giants, hermaphrodites, imbeciles, Jukes, Kallikaks, lunatics,morons, polydactyls, runts, simpletons, twins, and Zeros: ina word, with pathological phenomena in a very broad sense. Thisstatement, intended as a reflection on genetics, carries with it animplication that a study dealing with such material cannot be offirst rate importance. Such condemnation will probably be receivedby pathologists with the kind of smile it deserves, and I feelthat I am not likely to be called upon here to answer such an indictment.Nevertheless, I am going to ask your indulgence, for amoment, since this slightly malicious statement should not be allowedto pass unchallenged, both because it is inaccurate, and because,even were it true, the result of such work might still be ofmore importance than its critics seem to realize. The source ofthis criticism is not without significance. It comes almost alwaysfrom those whose interests lie in the field of evolution—in the old-fashioneduse of that word. Now the articles of all evolutionaryplatforms include a plank about heredity. This plank is for themost part an ancient article that has been worn pretty thin. It isdifficult to replace it (or at least it is supposed to be difficult to replaceit) with the new wood of Mendelian genetics. Hence, Ithink, originates the criticism referred to.
It is true that the student of Mendelian heredity does not oftentrouble himself about the nature of the character that he studies.He is concerned rather with its mode of inheritance. But thegeneticist knows that opposed to each defect-producing element[2]in the germ-plasm there is a normal partner of thatelement which we call its allelomorph. We can not study the inheritanceof one member of such a pair of genes without at thesame time studying the other. Hence whatever we learn aboutthose hereditary elements that stand for defects, we learn just asmuch about the behavior of the normal partners of those elements.In a word, heredity is not confined to a study of the shuffling ofthose genes that produce abnormal forms, but is equally concernedwith what is going on when normal genes are redistributed. Thismethod of pitting one gene against the other furnishes theonly kind of information relating to heredity about which we haveprecise knowledge.
In man and in domesticated animals we find that individualsappear occasionally that are defective in one or another respect.Some of the defects are inherited. Rarely a new one appears thathas not been seen before. But the majority of them are reappearancesof characters that have been carried under the surfaceas recessive genes in the germ-plasm. Today we recognize thateach of these modifications, if recessive, has first arisen as a mutationalchange in a