March, 1928 



EVOLUTION 



Page Five 



two million years to lose one tusk, the Horse a million 

 years to lose one toe. She gave Man five million years 

 to lose his tail; we carry around five bones of it yet. 

 A half-million years ago she stood Man on two feet; 

 our bodies are not yet adjusted to an upright gait. 



It is curious that Man trusts his voice to the telephone 

 and his family to the motor car, while he still clings, 

 like the poet's vine to the moudering wall, to his ancient 

 notions about his own nature. It was more than 200 

 years after Man knew that the earth revolves once every 

 twenty-four hours, that he discovered his own blood com- 

 pletes its circuit every twenty-three seconds. He can pre- 

 dict comets, but not wars, famines, or elections. He 

 knows his Ford's viscera better than he knows his own. 

 He rears calves more intelligently than he raises chil- 

 dren. He does not know why he suffers from rupture 

 or drops dead of heart-failure: or that he has hare-lip 

 because there were Sharks in his ancestry, and cleft palate 

 because he is of the line of Amphibia and Reptiles. 



East is East and West is Europe, said Kipling, there- 

 by insinuating grave error. But had he said that Susie 

 O'Grady and the Chinese lady are sisters under the skin. 



he w-ould have served truth. What we should like to 

 know is: why is their skin different? Or why an East, 

 or a Chinese lady — or women at all? And if Man's 

 nature is incurable, are his habits? Or is Man the onlv 

 dog that cannot learn new tricks, the only machine that 

 defies law, the only animal that cannot be understood? 



What are we? Before we can answer that question we 

 must know something of our physical body: what it is, 

 where it comes from, who made it, what it is good for. 

 what is its upkeep. Why so many sizes and colors; will 

 the color fade; is one color, size, or sex better than an- 

 other? Why do so many fail before they are used up, 

 v.hy do they wear out at all? Is it coming or going, 

 is there likely to be a new model out soon, and will it be 

 better (and if so, in what respect), or cheaper? 



When we know this body of ours we begin to know- 

 what we are — and that will help us to understand whv 

 Man made culture and why we call our culture Civiliza- 

 tion and think it pretty good. It will also help us to 

 understand why the old lady who lost her petticoat in 

 the market-place got frightened when she discovered she 

 had legs — and whv her dog barked at her. 



X-Rays Stimulate Variation 



Beloiv we reprint from "Science" of January 21th. 

 1928, an abstract of the paper by Dr. H. J. Muller of the 

 University of Te.-cas presented before the Joint Genetic 

 Sections of ih-e American Society of Zoologists and the 

 Botanical Society of America, at their Nashville meeting. 

 Awarded the American Association Prize of one thousand 

 dollars for the most notable contribution to the advance- 

 ment of Science. We hope to have a less technical presen- 

 tation of this tremendously important subject soon. 



"The Effects of X-Radiation on Genes and 

 Chromosomes" (Abstract) 



THIS paper reported the author's experiments of the 

 past fifteen months on the hereditary effects of X- 

 rays applied to the fruit fly, Drosophila melanogaster. 

 By means of special courses, the discrimination of muta- 

 tions in individual genes from genetic recombinations of 

 various sorts (due to segregation, non-disjunction, etc.), 

 was facilitated, and lethal as well as visible changes were 

 rendered detectable. Results in the second and later gen- 

 erations, based on several thousand cultures, showed that 

 gene mutations had occurred in the most heavily treated 

 germ cells at about 150 times the frequency of those in 

 the controls, derived from the same source, while in germ 

 cells less heavily treated the result was intermediate. 

 Germ cells in all stages studied were susceptible to the 

 effect: these included oogonia. ova, spermatozoa shortlv 

 before fertilization, and spermatozoa when rayed either 

 in the male or in the female receptacles six or more 

 days prior to fertilization. 

 " The induced mutations resembled spontaneous ones, 



inasmuch as: (1) The great majority were lethal; of 

 the rest most, but not all, reduced viability or fertility- 



(2) Recessives greatly outnumbered definite dominants. 



(3) Many of the visible effects were relatively incon- 

 spicuous. (4) Though "new" mutations were somewhat 



more frequent, there were also numerous repetitions of 

 familiar mutations. (5) All regions of the chromatin 

 were affected, but the induced mutations were more dense- 

 ly distributed in those regions of the linkage map in 

 which more spontaneous mutations have occurred. 

 (6) Multiple allelomorphism occurred. (7) So also did 

 reverse mutation of genes already mutant when treated. 

 Tlie two latter facts argue against the effects always be- 

 ing complete losses or inactivations. (8) Though point- 

 mutations were the rule, there was an occasional "line- 

 mutation" involving a row of neighboring genes, as if 

 by an electron that had passed parallel to the chronio- 

 nema. (9) The vast majority of the treated genes, both 

 mutant and normal-seeming, remained stable in their 

 inheritance throughout succeeding generations, though 

 at least one case of an "eversporting" condition arose. 



Evidence was secured (by making use of non-disjunc- 

 tion) that only one of the two identical genes, or allelo- 

 morphs, present in a diploid cell, is caused to mutate at 

 a time. The effect on a given gene, in a haploid germ 

 cell, is "fractional," in that only a fraction of the re- 

 sulting embryo will receive mutant gene material, the 

 remainder being of normal gene content. Since there is 

 no evidence of an indiscriminate intermingling of the 

 mutant and normal tissues thereby arising, it becomes 

 unlikely that the gene is compounded of many inter- 

 changeable members. This is also evidenced by the 

 stability of treated genes in heredity. 



Besides gene mutations, frequent rearrangements of 

 gene order — involving inversions, translocations', dupli- 

 cations, etc., of chromosome sections — were found, by 

 genetic evidence, to be produced by X-rays. These pro- 

 vided information concerning various questions. For 

 example, cytological verification of two such cases yield- 

 ed direct evidence for the physical validity of the link- 

 age maps and of the corollary theory of crossing-over. 



