is agreed that the highly developed tribal civilizations of West 

 Africa arose in connection with yam cultivation. Alexander and 

 Coursey {!)- have collected the sparse information about yam 

 domestication and have drawn a fairly detailed picture of what 

 might have happened during the course of domestication. 



The succulent tubers of yams were probably encountered 

 many times by primitive food-gathering peoples roaming the 

 forests of Africa. (Indeed, wild yams are still sought.) Among 

 the many kinds of yams, they were able to distinguish the poison- 

 ous species, which they detoxified by soaking the macerated tuber 

 in water. In spite of the risk associated with them, they have 

 continued to be prized even in modern times, although the con- 

 venience of the nonpoisonous forms has probably led to their more 

 frequent use. 



Domestication might have occurred at the homesite. Tubers 

 carried there and saved for later consumption might have sprouted 

 and developed new plants, or the woodier head pieces that are 

 often discarded might have sprouted. The idea for planting yams 

 could have come from the observation that plants near the home 

 are more convenient to use. 



On the other hand, Coursey and Coursey (10) have sug- 

 gested that the beginnings of yam cultivation might be found in 

 religious sanctions against the out-of-season use of the tuber. 

 Such sanctions effectively prevented the premature use and de- 

 struction of plants before propagation could be achieved. Further 

 steps in protecting yams were then considered. It is probable that 

 the cultivation of the yam, which requires a minimum of 6 months, 

 was associated with the establishment of villages. These, in turn, 

 made stable agriculture possible. 



D. rotundata appears to be a fairly ennobled species. Although 

 sexual fertility has declined, it has not been lost completely, as in 

 the case of D. alata. Wild forms are not definitely known, but 

 many cultivars look like the wild D. praehensilis Benth. and other 

 related species. It is highly probable that during domestication of 

 D. rotundata a sporadic exchange occurred between the cultivated 

 and wild forms. Through occasional hybridization with wild forms, 

 the cultivated types were enriched and their evolution was 

 encouraged. On the other hand, D. cayenensis is definitely a more 

 primitive species. Wild forms can be found as far west as Sierra 

 Leone and are used as food without cultivation. 



The development of improved strains may have been an 

 unconscious process. Generations of planting from the better culti- 

 vars followed by frequent outcrossing is probably the most effi- 

 cient technique for long-term plant breeding. But the historical 



2 Italic numbers in parentheses refer to items in "Literature Cited," p. 35. 



2 



