Page Twelve 



EVOLUTION 



January, 1938 



The Research Front 



Speeding Up Evolution 



DISCOVERY of a method of caus- 

 ing evolution was announced at 

 the recent meeting of the National 

 Academy of Sciences by Dr. Albert F. 

 Blakeslee, Director of the Station tor 

 Experimental Evolution of the Car- 

 negie Institution of Washington. 



For some time it has been known 

 that, among animals and plants alike, 

 parents transmit their traits to their 

 offspring by means of chromosomes, 

 little "threads of lite", on which the 

 real heredity bearers, the genes, are 

 located somewhat like tiny beads on 

 a string. A set ot these chromosomes 

 is inherited from each parent, carrying 

 a full complement of genes for trans- 

 mitting all the various characteristics 

 of the parent plant or animal. These 

 merge, and in that merger the charac- 

 teristics of the offspring are deter- 

 mined. If nothing has happened to 

 change the genes, then "like begets 

 like" and the children will be like 

 their parents. 



But we know that heritable varia- 

 tions, or mutations, do occur in nature. 

 The young are not always like the old. 

 A great many instances have been ob- 

 served where new characteristics have 

 come into being. Such mutations oc- 

 cur when something has happened to 

 the genes, causing them to transmit to 

 posterity a message different from that 

 received from their ancestors. Plant 

 and animal breeders are constantly on 

 the lookout for suitable mutations with 

 which to "breed up" seed and stock. 



How to affect the genes and cause 

 mutations artificially and thus speed up 

 evolution is a problem that has chal- 

 lenged the attention of scientists for 

 a long time. In Volume III, Number 

 1 of EVOLUTION, Dr. H. J. Mueller 

 described a method for bringing this 

 about by means of X-rays. Scientists 

 in many Agricultural Colleges are now 

 experimenting on various plants with 

 this method. 



Dr. Blakeslee experimented along a 

 different line. He tried out the effect 

 of various chemicals in his effort to 

 induce hereditary mutations. And he 

 found that a chemical, colchicine, 

 would cause mutations in plants, 

 doubling the chromosomes and genes, 

 (distinguished from mutations due to 

 changes within the genes ) . 



He reports: "The alkaloid col- 

 chicine we have found will induce an 

 abundant production of branches with 

 doubled chromosome number. When 



seeds are heavily treated all the seed- 

 lings may be affected. Doubling in 

 adult tissue has been induced by im- 

 mersion of twigs in solutions and in 

 agar, by treatment of buds with mix- 

 tures ot colchicine and lanolin and by 

 spraying with solutions. By the use 

 ot colchicine changes have been in- 

 duced which are interpreted as being 

 due to doubling of chromosomes in 

 the following genera: Datura, Portu- 

 laca, Cosmos, Phlox, Nicotiana, and 

 several others. 



"If control of chromosome doubling 

 proves of general application, as seems 

 to be the case, the plant breeder will 

 be able to work with greater precision 

 in his efforts to control the evolution 

 of economic forms of plants propa- 

 gated vegetatively as well as those 

 produced by seed. Starting with a 

 sterile hybrid, a pure breeding double 

 diploid has been synthesized, having 

 hybrid vigor and the desirable charac- 

 teristics of tetraploidy. Doubling the 

 chromosome number would give en- 

 larged flowers and fruits to the horti- 

 culturist. In addition to increase in the 

 size of the organs of plants, doubling 

 the chromosome number has changed a 

 self sterile to a self fertile form, 

 changed a dioecious to a hermaphro- 

 ditic race and an annual into a peren- 

 nial, and has increased winter hardi- 

 ness. In Zoology the causing of chro- 

 mosome doubling is an unexplored 

 field, but it will probably be a fertile 

 one. Tlie ability to induce chromo- 

 some doubling therefore is of impor- 

 tance to practical as well as theoretical 

 genetics." 



{In an early issue Evolution will bring 

 its readers more details regarding Dr. 

 Blakeslee' s epoch making discovery.) 

 • 



The Borderland of Life 



TWO reports made at a Symposium 

 on Biophysics, just held at the 

 University of Pennsylvania under the 

 auspices of the American Institute of 

 Physics and the Eldridge Reeves John- 

 son Foundation for Medical Physics to 

 apply the findings of modern physics 

 to solution of biological problems, will 

 be of special interest to readers of 

 EVOLUTION. 



Dr. Wendell M. Stanley of the 

 Rockefeller Institute for Medical Re- 

 search, who achieved fame two years 

 ago with the successful isolation in 

 crystalline form of the virus that causes 

 tobacco mosaic disease, reported the 

 isolation of two viruses causing disease 



in animals. Like the virus of the 

 tobacco mosaic disease, these viruses 

 are not small living bacteria, as had 

 been supposed, but giant protein mole- 

 cules, resembling the ordinary protein 

 molecules of protoplasm but larger, 

 and having the life-like ability ot re- 

 producing themselves rapidly when in 

 contact with living matter. 



It appears that in these viruses Dr. 

 Stanley has discovered forms that exist 

 in the "twilight zone" between the liv- 

 ing and the non-living, having certain 

 properties of each, but belonging to 

 neither. They help to bridge the gap 

 between the organic and the inorganic 

 worlds. They furnish one of the most 

 important "missing links" that funda- 

 mentalists have always challenged the 

 evolutionists to find. 



The study of these invisible forms, 

 so small that they pass through the 

 finest porcelain filters, but capable of 

 causing many of the most serious dis- 

 eases in plants and animals, has occu- 

 pied men of science for many years. 

 But not until Dr. Stanley isolated the 

 tobacco mosaic virus was their nature 

 definitely understood. They are mole- 

 cules of protein, similar to the pro- 

 tein that exists in all protoplasm, but 

 in a suitable environment they seem to 

 "come alive" and reproduce their kind 

 indefinitely. 



"In view of the properties which 

 this protein possesses," says Dr. Stan- 

 ley, "the borderline between the liv- 

 ing and the non-living tends to be- 

 come non-existent, for although it pos- 

 sesses properties which have been re- 

 garded as characteristic of living 

 things, such as specificity of host-range 

 and the ability to reproduce and mu- 

 tate, it is nevertheless a protein mole- 

 cule, and as such may be regarded as 

 non-living." 



To the evolutionist one of the most 

 interesting features of this protein 

 molecule is that, in common with all 

 forms of life, it is subject to mutation, 

 and therefore to the process of evolu- 

 tion. Such virus mutations have al- 

 ready been observed in nature, and 

 have even been brought about artifi- 

 cially in the laboratory by chemical 

 means. Through mutation a virus 

 growing in connection with one kind 

 of plant becomes adapted to existence 

 on another plant, or capable of pro- 

 ducing a different disease from its an- 

 cestral virus. This protein molecule 

 seems to be closely akin to the gene, 

 the heredity bearer, through which the 

 traits of living forms are transmitted 

 from generation to generation. It may 

 be that here we have the key with 



