East: As Genetics Comes of Age 



209 



sentially their method was to measure 

 the degree of association between par- 

 ents and offspring for any particular 

 character. It was wholly a group 

 method, and by its very nature pre- 

 cluded both the analysis of individual 

 cases and the utilization of biological 

 facts among the premises. Its chief 

 generalization, the law of ancestral 

 heredity, wherein the correlation of 

 characters among blood relatives was 

 interpreted as showing the inheritance 

 of an individual to be made up of a 

 series of contributions, one-half from 

 the parents, one-fourth from the grand- 

 parents, and so on, has been shown to 

 be erroneous. Having proved no 

 stimulant to productive investigation, 

 its discussion has passed from the 

 genetic literature of today; but the 

 mathematical procedure evolved by 

 the Galtonian school has proved to be 

 extremely helpful. 



The earlier genetic theories of the 

 period under consideration necessarily 

 were highly speculative because of the 

 paucity of known facts ; but the funda- 

 mental postulate of each, active ultra- 

 microscopic living units, has been 

 retained in the genetic theory of today. 

 Darwin's provisional hypothesis of 

 pangenesis (1868), for example, as- 

 sumed that such particles, the gem- 

 mules, were given off at all times by 

 every cell, and passed to all parts of 

 the body including the germ cells. 

 He thus accounted vaguely for the 

 inheritance of acquired characters and 

 for regeneration of parts, as well as 

 for ordinary heredity. 



Among several contemporary modi- 

 fications of this type of theory was 

 that of De Vries (1889), who assumed 

 that the corpuscles, which he called 

 pangens, represented potential elemen- 

 tary body characters rather than cell 

 qualities, and that the universe of 

 their activity was the cell rather than 

 the body. 



It is clear, even with only a glimpse 

 of such theories, that they could satisfy 

 none but the philosophically inclined. 

 They did little or nothing toward 

 stimulating work designed to test the 

 points involved. 



A different fate met the speculations 

 of Nageli (1884). Here was postulated 

 two types of protoplasm built up of 

 physiological units, the micellae: the 

 one was nutritive in its functions, and 

 required no particular architecture; 

 the other, the idioplasm, a structure of 

 elaborate constitution, was built of 

 units which represented the potential 

 elementary characters of the organism. 



weismann's theory 



Utilizing this conception, Weismann 

 (1892) evolved a theory which more 

 nearly fulfilled the requirements of an 

 experimental working hypothesis than 

 any of those previously outlined. The 

 idioplasm or germplasm he identified 

 with the chromatin of the nucleus. 

 His ultimate physiological unit, the 

 biophore, was the biological atom 

 active in building up organic charac- 

 ters. Grouped together into higher 

 units, the determinants, these cor- 

 puscles controlled the specialization of 

 cells. The various determinants of an 

 organism made up the ids contributed 

 by past generations. The ids, if more 

 than one, might differ slightly among 

 themselves, thus governing variation 

 within the species. They formed the 

 chromosomes, or idants, by arrange- 

 ment in a linear series. 



Denying the inheritance of acquired 

 characters, and doing much toward 

 demolishing the fallacious logic put 

 forth as proof at that time by adher- 

 ents in the belief, Weismann outlined a 

 very stimulating conception of heredity 

 on this basis. The immortal germ- 

 plasm was assumed to be set apart at a 

 very early cell division and passed along 

 unchanged to the next generation, 

 except as the activities of the 

 living units produced occasional 

 changes in its constitution. A pro- 

 vision for accurate equational division 

 of the chromosomes and their reduction 

 in number at the maturation of the 

 germ cells was thus demanded, pre- 

 dicted and afterwards realized — ^though 

 not precisely in the way he supposed — 

 by discoveries in the field of cytology. 



Weismann further accounted for 

 evolution by a selective struggle be- 



