248 GENETICS AND PLANT BREEDING 



Clearly, if the general life expectancy bomb. Even more important, it was a 



doubles, then even without any in- large factor in preventing this time the 



crease in births at all there are twice aftermath of hunger that followed the 



as manv mouths to feed at any one end of the first World War; for the 



time as there were before. But there amount of food we were able to ship 



arc also more than twice as manv adults to the desolated countries of Europe 



with unmodified (or but slightly in 1946-47 was more than equalled by 



moderated) yearning to have children the increase in the com crop attribut- 



and rear families. 'Hie world popula- able to the planting of hybrid com. 



tion has soared, in spite of wars and The hunger and chaos of Eastem 



famines, from one and a half billions of Europe in 1918 and 1919 fumished 



people, a centur)' ago, to two and three- Communism with the seedbed in 



fourths billions today. Fertile land is which it first rose to political domina- 



almost fully occupied. How can we tion in Russia. The curbing of the 



feed another billion people, whom we spread of Communism in Westem 



may expect inevitably to arrive before Europe after the more recent World 



the slowly dropping birth rate overtakes War may in a vcr)' considerable meas- 



the still declining death rate? Tlie im- ure have been due to the boon of 



mediate answer, if there be one, lies in hybrid com, as Paul Mangelsdorf of 



the almost unheralded achievements Harvard University has claimed, 



of geneticists in increasing the food It is of some interest, therefore, to 



supply. see just what G. H. Shull did with his 



On September 28, 1954 there died corn plants. He started out with the 



in Princeton, New Jersey, a geneticist intention of studying the inheritance 



who never received a Nobel prize or of quantitative characters, such as 



made a fortune. To most Americans yield, in order to see whether these fol- 



George H. Shull remains completely lowed the laws of Mendelian inheri- 



unknown. Yet this man, together with tance; and he began by inbreeding his 



a few others who made his theoretical lines. He found that this inbreeding 



achievement a practical possibility, has brought out a number of hidden, 



brought about a 20-30 per cent in- deleterious hereditary characteristics, 



crease in the United States yield-per- and that the inbred strains showed a 



acre of corn crop with no further re- marked loss of both vigor and produc- 



quirement for labor, and has added tiveness. Eventually he obtained very 



literallv billions of dollars to the in- pure strains of great uniformit}^ though 



come of our nation. from the point of a farmer totally 



In fact, a true agricultural revolu- worthless, runty, and weak, with small 



tion, though scarcely recognized, has ears bearing few seeds, and of course 



resulted from the discovery of hybrid very low in yield. When, however, two 



corn. During the war years 1942-44, in of these inbred lines were crossed to- 



the face of acute shortages of labor gether, there was a phenomenal im- 



and of bad weather, and at a time provement in the hybrids, 



when the corn acreage of the United In 1917 Donald F. Jones, at the 



States was still only about one-half Connecticut Agricultural Experiment 



planted with hvbrid corn, the increased Station, invented the so-called "double 



\ield amounted to approximately cross," with quite the opposite effect 



twenty per cent— a total of 1,800,000,- from that of the usual connotation. 



000 bushels worth two billion dollars. By crossing together the two hybrids 



Hybrid com thus in a sense paid for produced from the single crosses of 



the entire development of the atomic four different inbred lines, A, B, C, and 



