3 io 



THE QUARTERLY REVIEW OF BIOLOGY 



Goldschmidt, '17, '2.0c, 'zz, 'z^c, 'Z7D). 

 Thus we have the four sets of facts: 1. 

 At the beginning of development two sets 

 of genes, male and female, are present in 

 definite quantities; z. The relation or 

 grade of balance of these two quantities 

 decides whether normal sex is developed 

 or a definite step in a continuous series of 

 intersexuality up to sex-reversal; 3. Nor- 

 mal sex, increasing intersexuality and 

 sex-reversal are determined by the non- 

 occurrence or earlier and earlier incidence 

 of the turning point; 4. The time of 

 incidence of the turning point is a simple 

 function of the relative quantities of the 

 M and F genes, namely of the degree of 

 their unbalance. These facts, based on an 

 extraordinarily diversified but always 

 consistent set of experimental and morpho- 

 logical data, are linked together by the 

 conclusion that a) both the F and M genes 

 produce chains of reactions of definite 

 velocities, b) that these velocities are 

 ceteris paribus proportional to the absolute 

 quantities of the genes, c) that the series 

 of turning points are points of intersection 

 of the curves of the two reactions, and d~) 

 that therefore the position in time of 

 these points of intersection is a simple 

 function of the proportion of the two 

 quantities of the genes in question. It 

 should be emphasized that every criti- 

 cism of these conclusions is worthless 

 without a proof that either the underlying 

 facts are not correct or that other and 

 better conclusions can be drawn from the 

 facts. 



Here then has been derived for one type 

 of genes, the sex -genes, a definite idea of 

 their action: the production of chains of 

 reaction of definite velocities which are 

 a function of the quantity of the gene in 

 question. As early as 1917 the present 

 writer, after having studied another case, 

 which led to the same conclusions, had 

 enlarged them to apply to all genes. In 



'zob and 'z7a he used this insight as the 

 basis for developing a general theory of 

 heredity, a theory which has been called by 

 some critics the beginning of a new era in 

 genetics and by others bunkum, neither 

 sound genetics nor sound physiology; a 

 reception which in view of historical 

 parallels seems rather encouraging to the 

 author. But this generalized theory may 

 be dismissed here and only such material 

 reviewed as furnishes further evidence on 

 the nature and action of the gene. 



2. Multiple allelomorphism 



The different sex genes of the races of 

 the gipsy moth behave genetically like 

 multiple allelomorphs; our work therefore 

 demonstrated for the first time that a 

 series of multiple allelomorphs of a 

 definite gene was really a series of different 

 quantities of this gene. There is a 

 possibility that sex-genes are different 

 from other genes; discarding this the 

 present writer came to the conclusion 

 ('17, 'zob, *Z4) that most if not all 

 multiple allelomorphs are of the same 

 order. Two ways of proving this 

 generalization were visible, first the 

 indirect way of demonstrating that as in 

 the case of intersexuality series of multiple 

 allelomorphs were linked up with reac- 

 tions of definite velocities, and second the 

 direct way of proving the quantitative 

 nature of multiple allelomorphs. The 

 first line of demonstration was followed by 

 the present writer in his work on the 

 markings of gipsy-moth caterpillars ('17, 

 'zob, 'Z4), after Sew all Wright had come 

 very near to the same result in his work on 

 rodents ('16, '2.5)- A similar demonstra- 

 tion for non-multiple allelomorphic genes 

 was given recently by Ford and Huxley 

 CZ7). The second direct way of approach 

 has only recently been made possible 

 through the brilliant work of Sturtevant 

 on the bar series of Drosophila CZ5). 



