HYBRIDIZATION IN THE EVOLUTION OF MAIZE 177 



Prehistoric Mestizos,^ thirteen in number, are races which are believed to 

 have arisen through hybridization between Ancient Indigenous races and 

 Pre-Columbian races and hybridization of both with a new entity, teosinte. 

 The term })rehistoric rather than pre-Columbian is used for this grouj) be- 

 cause, although all are prehistoric in the sense that there is no historical evi- 

 dence of their origin, it is not certain that all are pre-Columbian. 



Modern Incipient races are those which have come into existence in the 

 post-Columbian period. These races, of which four are recognized, have not 

 yet reached a state of genetic equilibrium. They are recognizable entities but 

 are still changing. 



The seventeen races comprising the two last groups all appear to be prod- 

 ucts of hybridization, either between races in the first two groups, or between 

 these races and teosinte. In several cases, secondary and even tertiary hy- 

 bridization seems to have occurred. 



That a race is the product of previous hybridization seems highly prob- 

 able when the following four kinds of evidence are available. 



1. The race is intermediate between the two putative parents in a large 

 number of characteristics. 



2. The putative parents still exist and have geographical distributions 

 which make such hybridization possible and plausible. 



3. Inbreeding of the suspected hybrid race yields segregates which ap- 

 proach in their characteristics one or the other of the two putative parents — 

 in some cases both. 



4. A population quite similar to the race in question can be synthesized 

 by hybridizing the two putative parents. 



Wellhausen el al. (1951) have presented all four kinds of evidence for the 

 hybrid origin of a number of the present-day Mexican races. They have pre- 

 sented similar but less complete evidence for the remainder. 



The variety Conico, for example, which is the most common race in the 

 Valley of Mexico, is clearly the product of hybridizing the ancient Palomero 

 Toluqueno with the exotic Cacahuazintle. Conico is intermediate between 

 these two races in many characteristics. The two putative ancestral races still 

 are found in isolated localities in the Valley of Mexico. The race is interme- 

 diate in its characteristics between the two suspected parents. Inbreeding 

 yields segregates which almost duplicate in their characteristics one of the 

 parents — Palomero Toluqueno. Segregates approaching the other suspected 

 parent, Cacahuazintle, also result from inbreeding but this parent is never 

 exactly duplicated. Obviously the race has become something more com- 

 plex than a mixture of equal parts of two earlier races. Nevertheless the 

 crossing of Palomero Toluqueno and Cacahuazintle still produces a hybrid 

 which in many respects is scarcely distinguishable from the suspected hybrid 

 race. The data in Table 11.1 show that Conico is intermediate between Palo- 



1. Mestizo is the Latin-American term for a racial hybrid. 



