FOSSIL PEDIGREES 85 



yond our powers of imagination to conceive. If both these can 

 survive,- why has their common parent perished? Why, when 

 they cross, do they not reconstruct it instead of producing 

 partially sterile hybrids? I take this example to show how 

 entirely the facts were formerly misrepresented." {Heredity, 

 Smithson. Inst. Rpt. for 1915, p. 369.) 



Similarly, T. H. Morgan has shown, with reference to 

 mutants, the fallacy of inferring common descent from the 

 phenomenon of intergradence, and what holds true for a series 

 of intergradent mutants would presumably also hold true of 

 a series of intergradent species, could such a series be found 

 and critically distinguished from hybrid and mutational inter- 

 mediates. In short, the Darwinian deduction of common ori- 

 gin from the existence of intergradence must now be regarded 

 as a thoroughly discredited argument. "Because we can 

 often arrange the series of structures in a line extending from 

 the very simple to the more complex, we are apt to become 

 unduly impressed by this fact and conclude that if we found 

 the complete series we should find all the intermediate steps 

 and that they have arisen in the order of their complexity. 

 This conclusion is not necessarily correct." (''A Critique of 

 the Theory of Evolution," p. 9.) Having cited such a series 

 of gradational mutations ranging between the long-winged, 

 and completely wingless condition, in the case of the Vinegar 

 Fly {Drosophila melanog aster) , as well as two similar graded 

 series based on pigmentation and eye color, he concludes: 

 '^These types, with the fluctuations that occur within each type, 

 furnish a complete series of gradations; yet historically they 

 have arisen independently of each other. Many changes in 

 eye color have appeared. As many as thirty or more races 

 differing in eye color are now maintained in our cultures. 

 Some of them are so similar that they can scarcely be sepa- 

 rated from each other. It is easily possible beginning with 

 the darkest eye color, sepia, which is a deep brown, to pick 

 out a perfectly graded series ending with pure white eyes. 

 But such a serial arrangement would give a totally false idea 



