406 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



exhibited in organisms heterozygous for mutated and unmutated 

 genes into that produced by the most favorable gene combination. 

 Thus, if a tall plant mutated to a short one and the combination of 

 the two was intermediate and less favorable than the short, then in 

 time, through the gradual accumulation of supplementary genes, short 

 plants would come to be dominant to tall ones. If, on the other hand, 

 tall was the favorable size then in time tall would become dominant 

 and the two genes, tall and short, that in the beginning gave in the 

 segregating generations a ratio of one tall to two intermediate to one 

 short would give three tall to one short. 



For selection to operate to accumulate conditioning factors for 

 mutated genes the two gene forms must be brought together. If a 

 gene change occurred within a species this changed gene when intro- 

 duced into another species where no such change had taken place 

 should give an intermediate first generation and exhibit a 1-2-1 

 segregation in the second generation. However, if the two species 

 were not ^\^dely separated and intercrossing had occurred permitting 

 both species to accumulate the necessary conditioning factors then 

 the reaction should be one of clear-cut dominance. 



As is often the case when promising leads reach an impasse, a com- 

 bination of all of them offers hope of further progress and the origin 

 of maize may involve all the processes suggested — selection, mutation, 

 hybridization — and also an extinct plant having characteristics com- 

 plementing those of teosinte but not of sufficient merit from the stand- 

 point of man to have entered into his diet. By the accidental hybridi- 

 zation of teosinte or some mutations of teosinte with some such grass a 

 plant useful to man could result. This hybrid need not have occurred 

 often but selection of the fluid germ plasm resulting could produce a 

 new cereal relatively rapidly. 



Even under this combination of processes maize stands as having 

 been created and fLxed botanically at such a remote period that one 

 and only one sort of maize became established over the Americas 

 leaving no trace of its intermediate forms. Naturally, if hybridization 

 was an important factor in the development of maize, the center of 

 origin was very circumscribed, for presumably such chance hybrids 

 were not of common occurrence. Under this limitation the new hybrid 

 may have been fashioned into maize rapidly by means of selection 

 without starting a chain of distribution of pre-maizelike plants. The 

 distribution would not have begun or would not have gone far until 

 the main characteristics of corn were fixed. This would accord well 

 with the evidence on the distribution of maize. 



Whatever explanation is finally proved to be correct, everyone 

 agrees that in the form we know it today maize is the result of man's 

 skillful efforts. Whether it was derived from a hybrid, an extinct 

 plant, a mutation from teosinte, or by orthodox selection, generations 



