Maize for the Gods: Unearthing the 9,000-Year History of Corn

The complete story of maize in Native American culture. Starts with the firm identification of teosinte as the sole origin for the genetic packages of landrace varieties that were eventually found in cultivation in the New World. There are several varieties of teosinte (Zea mays) and a related genus Tripsacum, but elaborate DNA analysis shows that corn is derived almost entirely from Z mays subspecies parviglumis growing in the Balsas River region of southwestern Mexico, with a slight admixture of subspecies mexicana growing at higher elevations and introducing a genetic component into varieties suitable for those locations. The specific genetic modifications that served to make the transition include genes that: 1) convert the bundle of seed-bearing spikes with the two rows of hard kernels in a readily shattering teosinte seed head into a multi-rowed set of kernel pairs exposed on a hard cob and surrounded by a sheath of leaves to make the husk; and 2) force the plant to drop its multi-stemmed form to maintain a single central “trunk” with a pollen-bearing tassel at its top. Various lines of evidence are used to show that the genetic signature of corn first diverged from the wild teosinte about 9000 years ago, first miniature corn cobs show up at archaeological sites in Mexico about 6000 years ago, and isotope signatures in human remains indicate that corn became a staple diet for people only about 3000 years ago. The transition to heavy reliance on a corn diet is tied to the formative period of the Olmec culture. The stable carbon ratio gets complicated by the heavier isotope content of seafood to produce a signal that looks like C4 carbon uptake, but the ambiguity can be eliminated by considering the stable nitrogen ratio where the heavier isotopes are concentrated in the food chain. The primary reliance on corn applies only north of Mexico because people to the south continued to have other sources of starch (primarily manioc and potato) available in quantity. Corn makes its appearance in Arizona and New Mexico about 4000 years ago, and is accompanied by processing equipment and effigies suggesting continuity with Mesoamerican cultures that went before. Corn processing is described as either the grinding of hard corn kernels, or the pulverizing of soaked and boiled corn to make tortillas, tamales, and porridge. The reliance on a diet of corn is shown to require processing with nixtamalization – soaking corn in alkaline solution to improve the availability of nutrients. This was almost always done using the ashes of trees such as juniper or oak, and ceramic colanders at archaeological sites are attributed to the processing of corn – either to rinse off the lime or to expose the boiled corn to alkaline wash. Eastern woodland Indians used wooden mortars and receptacles to pulverize the corn mixed with wood ash before boiling after the use of corn arrived sometime after 1000 CE. Although not stated explicitly, the author seems to suspect that teosinte was originally domesticated for the sugar-rich juice that could be squeezed from its stems in the production of fermented beverage rather than for its meager and hard-shelled seeds.

A fascinating and detailed history of how one of the most important world food crops came into existence. It is up to date with the current state of the science. Not too complex for the nonscientist to grasp but not so basic that an expert like myself was bored.

This is a good introduction to the paleo botany field and useful for anyone studying early agriculture or the history of the indigenous Americans. I am not an archeologist and realize their standards might be different than those of a physical scientists, but it does seem to me that this field often makes inferences on the basis of limited data without identifying alternate hypotheses. The material on isotopic analysis is especially problematic. We have trouble interpreting stable isotope results for modern crops with basically unlimited opportunities for sampling and evaluative variability and uncertainty. Drawing inferences about the