PAUL C. MANGELSDORF 



Harvard University 



Chapter 1 1 



Hybridization in 

 the Evolution of Moize 



All varieties and races of maize so far studied prove upon inbreeding to con- 

 tain numerous heterozygous loci, and all respond to inbreeding with a marked 

 decline in vigor and productiveness. Since contemporary maize is both 

 heterozygous and heterotic, it is probable that the factors which have been 

 responsible for bringing about the present conditions are also factors which 

 have played an important, if not the principal role, in the evolution of maize. 



All of the steps involved in the evolution of maize are not yet known. 

 Archaeological remains have told us something of the early stages of maize 

 under domestication, and we can draw additional inferences about its original 

 nature from its present-day characteristics. Our knowledge of the nature and 

 extent of its present variation, although far from complete, is already sub- 

 stantial and is growing rapidly. By extrapolating forward from ancient 

 maize, and backward from present-day maize, w^e can make reasonably valid 

 guesses about some of the intermediate stages and about some of the evolu- 

 tionary steps which have occurred in its history. 



The earliest known archaeological remains of maize, as well as the best 

 evidence of an evolutionary sequence in this species, occur in the archaeo- 

 logical vegetal remains found in Bat Cave in New Mexico in 1948. This ma- 

 terial which covers a period of approximately three thousand years (from 

 about 2000 B.C. to a.d. 1000) has been described by Mangelsdorf and Smith 

 (1949). It reveals three important things: (1) that primitive maize was both 

 a small-eared pop corn and a form of pod corn; (2) that there was an intro- 

 gression of teosinte into maize about midway in the sequence; (3) that there 

 was an enormous increase in the range of variation during the period of ap- 

 proximately three thousand years resulting from teosinte introgression and 

 interracial hybridization. 



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