New perspectives on the origin and evolution of new world domesticated plants: Summary

Abstract

It is quite apparent from the papers given at this symposium that molecular biology is now making great contributions to our understanding of the origin and evolution of crop plants. I should point out, however, that the more traditional approaches still have something to offer as was exemplified by Newstrom's paper on the chayote. I do not intend to examine all of the papers in any great detail; rather I prefer to see how some of them relate to two more general topics-(l1) the diffusion of crops between Middle America and South America and (2) the beginnings of domestication in eastern North America. In 1965 I reviewed all of the major crops of the Americas (Heiser 1965) and additional information was incorporated in later papers (Pickersgill and Heiser 1977; Heiser 1979). Although studies in the last two decades have given us a much better understanding of the early history of some of the plants, most of what I wrote in 1965 still holds. Surprisingly few of the crops of Mexico reached South America in prehistoric times and even fewer had penetrated Mexico from South America, particularly so if we accept an independent domestication of some crops in the two areas, such as species of beans (Phaseolus vulgaris L. and P. lunatus L.) which I suggested in 1965. Evidence for such has been presented here by Gepts. For some crops it was difficult to determine if their movement from one area to the other occurred in the preor post-historical period, and this is still true for some of them. Maize (Zea mays L.) is nearly always central to any discussion of prehistoric American agriculture, so it is most appropriate that I begin with it. In 1965, although it was clear that maize had one origin in Middle America, the question of a separate origin in South America was still maintained as a possibility. Bonavia and Grobman (1 9 89) still hold to a separate South American origin of maize, but I think that it is clearly one of the few Middle American plants to have reached South America from Middle America in prehistoric times. As Doebley has told us in this symposium, maize is derived from teosinte and moreover, as a result of his studies, we can now be fairly certain as to which of the teosintes gave rise to it. Some people, however, are still proposing that a wild maize was the progenitor (see Goodman 1987). Recently Lathrap (1987) has stated that among the "proto-crops" that flowed from tropical South America north were cotton and cacao. He cites Pickersgill and Heiser (1977) for cotton but, as they point out, there is no evidence for an interchange of the cultivated cottons (Gossypium hirsutum L. and G. barbadense L.) between Mexico and Peru in prehistoric times. For cacao he cites Marcos (1 9 73). However, I would still maintain my 19 65 assignment of the domestication of cacao to Middle America. My principal sources at the time were Sauer (1 9 51) and Cuatrecasas (1 964). The extensive and most valuable review of the early literature by Patiiio (1 9 63) also supports this position. Although wild Theobroma