Iowa State University
USDA-ARS North Central Regional Plant Introduction Station
Pioneer Hi-Bred International, Inc.
Crow Canyon Archaeological Center

Development of a research proposal for integrating molecular and anthropological approaches to understanding the co-evolution of maize and human cultures
--Deborah A. Muenchrath, Peter Bretting, J. Stephen Smith, and Karen R. Adams

Agriculture is embedded in the natural ecosystem and the human social system. It is the bridge between them. Norman Borlaug, 1990
The co-evolution of maize and humans in the Americas enabled both species to flourish over millennia. Their interrelationship is reflected in the maize and maize-based cultures found from Mesoamerica through the southwestern United States. Maize seed dispersal and maintenance depends on humans, and maize productivity influences human population sizes and migrations. Thus, the development of human cultures and the evolution of maize are closely intertwined.

Ancient, as well as contemporary, maize-human relationships hold lessons pertinent for germplasm and resource stewardship. Understanding the co-evolution of maize and associated human cultures may provide critical insights for charting future agricultural and societal development. Such an understanding may be achieved through innovative research that synthesizes the knowledge and methods of various disciplines and perspectives.

To discuss and explore collaborative, interdisciplinary approaches to the study of the interrelationships between maize evolution and human cultural development, a workshop was organized. It was sponsored by Pioneer Hi-Bred International, Inc. and hosted by the USDA-ARS North Central Regional Plant Introduction Station and Iowa State University, August 29-31, 1994 at Ames, Iowa. The workshop convened thirty individuals interested in maize and human cultures, including researchers from a variety of disciplines, and specialists in cultural heritage conservation and in germplasm management. Participants came from the United States and Mexico, and were affiliated with academia, industry, governmental agencies, tribal offices, museums, and non-profit germplasm conservation organizations.

Prior to the workshop, selected participants submitted background papers which summarized issues and common research methods of their respective disciplines. These compendia briefed all participants on archaeology and ethnobotany, plant germplasm management and breeding, molecular markers and genetic characterization of maize, and evolutionary interpretation of DNA data. At the workshop, displays illustrated the various approaches. Speakers introduced the concerns, challenges, and potential contributions, as well as limitations, of the various fields:

Participants toured North Central Regional Plant Introduction Station fields to view the phenotypic diversity exhibited among sixty maize landraces native to the United States and northwestern Mexico. They also visited the Station's seed storage facilities to learn more about maize germplasm management systems.

Participants gathered in two discussion groups, moderated by Drs. John Doebley and Peter Bretting. The groups' tasks were to: (1) identify areas of mutual interest across disciplines, (2) establish long-term research objectives, (3) explore approaches and technologies to address those objectives efficiently, and (4) outline specific research projects. Both groups determined that a descriptive database on modern and historic maize and an inventory of archaeological maize collections were required for future research. In addition, specific research issues, hypotheses, and appropriate technologies, materials, and sampling strategies were considered.

I. Geographic Focus. As conceived in this workshop, studies will focus initially on the maize and cultures of the southwestern United States and adjacent northwestern Mexico. This region has an extensive archaeological record, including a number of uncharred maize collections, continuity between ancient and contemporary indigenous cultures and agricultural systems, and connections with central Mexico, maize's center of origin. The project will eventually expand to other regions of the United States, particularly those encompassing the progenitor races of the highly productive Corn Belt Dents: the Northern Flint and Southern Dent races. Companion studies will trace maize phylogenies between Mexico and the United States.

II. Molecular Analysis. The criteria for identifying optimal molecular technologies emphasized that they: (1) be in the public domain, (2) be cost-effective, and (3) provide phylogenetic information. It was determined that molecular data on extant cultivars, experimentally-deteriorated specimens, and archaeobotanical specimens from ample collections should be analyzed molecularly to determine the feasibility and utility of the technologies before applying them to scarce archaeobotanical materials. Technologies for amplifying and preserving DNA from such archaeobotanical materials were discussed.

III. Archaeological Questions. Specific archaeological questions that would be more tractable to study by the approaches discussed include:

  • What patterns in maize genetic diversity occur over time on local and regional levels?
  • Did maize diversity in the southwestern U.S. result from several waves of introductions, or from in situ selections and divergence following an initial introduction? If there were a series of introductions, do these correspond with other evidence of trade connections?
  • What is the relationship of Utah-area Fremont Dent with other southwest maize?
  • When shifts in maize morphology occurred (e.g., decrease in ear row number), were there concurrent shifts in genetic patterns?
  • Do maize genetic changes correspond to changes in human material culture?
  • What is the relationship between the degree of maize genetic diversity and the periodic human population dispersals and aggregations observed in the ancient southwestern U.S.?
  • Can human migrations be traced through the distribution patterns of specific maize genes (allele distributions)?

  • The answers to the preceding questions have implications for modern germplasm and environmental management, plant breeding, and genetics.

    IV. Perspective of Maize-Based Cultures. A proposal to include the knowledge systems of indigenous peoples was presented by Ricardo Salvador. Dr. Salvador discussed the information about maize and human cultures that is encoded in the knowledge, languages, and traditions of Native Americans. Integrating these knowledge systems with those of the scientific community will enhance interpretations and understanding of human-maize relationships. Indigenous people should be consulted and included as an integral part of the planning and implementation of any research program examining maize evolution and human cultural development.

    V. Handbook on Maize Diversity. It was proposed that the information obtained through the research program be compiled into a comprehensive handbook on the indigenous maize races of the United States. Such references are currently available on the maize of Mexico, Cuba, Peru, and other Latin American countries. The version for the U.S. maize races would describe extant and ancient maize, and their relationships to each other and to non-U.S. maize. Descriptions of extant races would include ecogeographical, ethnographic, morphological, agronomic, physiological, molecular, and elemental data. Descriptions of ancient maize races would consist of morphological and molecular characterizations, as well as information from the archaeological record regarding the associated human culture. Interpretive sections would also be included. Such a reference would be useful to many fields of study. Additionally, an electronic version might be developed, which would contain a more complete database; this could be updated more rapidly and frequently and it would aid searches for specific information. Presently, we lack sufficient data to write such a volume. The research projects under consideration would contribute much of the necessary data, so that an ultimate outcome of the research program may include a handbook on U.S. maize.

    VI. Training Program. In addition to the scientific goals, a major programmatic objective is to train students in an interdisciplinary fashion. Students will be involved in each phase of the project. They will broaden their perspectives and knowledge, and develop new skills. Anthropology students will develop skills in agroecology, biology, and molecular biology; biology students will become more familiar with anthropological approaches. Core labs will be established at two or more universities for interdisciplinary training. Students will also serve as interns at other facilities as needed. A special effort will be made to include Native Americans and Hispanic students.

    In the final workshop session, moderated by Deborah Muenchrath, participants convened in a single group to draft conclusions and outline research initiatives. The research program proposal that emerged provides a stepwise, multi-disciplinary approach to the study of the co-evolution of maize and human cultures that will be significant to several disciplines. This research program will address issues relevant to archaeology, genetics, germplasm management, maize evolution, and plant breeding. It will examine modern, historic, and ancient maize and cultures and their evolution and relationships through time and across geographic areas. It will uncover patterns in both the genetic diversity among maize races and the connections among maize and human cultures. It will also contribute toward the conservation of indigenous human cultures and biological resources. It will provide technical and interdisciplinary training for students of anthropology, archaeology, molecular biology, genetics, genetic resource management, and agroecology. The program also will contribute data for development of a comprehensive, cross-disciplinary database and reference handbook on maize native to the United States. Table 1 summarizes expected outcomes.

    While the specific organization and funding details for such a comprehensive research program remain to be developed, its scientific basis was outlined during the workshop. Important elements of the research plan were identified and a timetable drafted (Table 2 A & B).

    Some initial elements of the project that are fundamental to subsequent research are already in progress, such as the development of suitable molecular technologies. An inventory of archaeological maize collections is essential for identifying the appropriate materials for morphometric and molecular characterizations. Results from initial morphometric and DNA analyses should help focus the larger, integrated, and multi-disciplinary research program.

    The workshop identified six specific technical areas of research:
    1) Develop microsatellite or simple sequence repeat (SSR) technology as a "fingerprinting" tool. Current elite inbred lines and segregating populations are now under analysis to develop and map SSR loci. As this technology is perfected, it will be incorporated into the proposed project.
    2) Obtain morphometric and SSR characterizations of extant races of maize in the United States, beginning with southwestern materials.
    3) Develop techniques for extracting DNA from archaeological maize specimens in suitable amount and of sufficient quality for SSR profiling. Evaluate the potential of conserving ancient DNA by amplifying the entire DNA extract.
    4) Apply SSR technology to archaeobotanical specimens to generate data to address taxonomic, phylogenetic, and cultural questions.
    5) Investigate the potential for elemental chemical analysis to match archaeobotanical specimens with their production locality.
    6) Investigate the genetic and physiological bases for maize adaptation to arid and high-elevation environments using quantitative trait loci (QTL) mapping.

    From this research, the following research data would emerge:

  • Morphometric and DNA descriptions of extant cultivars, which would contribute to generating a new or more comprehensive understanding of the genetic variability in extant races;
  • DNA descriptions of archaeobotanical specimens applicable to specific phylogenetic questions; and
  • Data and methodologies for further investigation of cultural, biological, and genetic issues.

  • A comprehensive study will demand cooperation and coordination among many researchers and organizations to utilize resources efficiently and to analyze data effectively. During the project, responsibilities and leadership will shift as the research emphases shift. Nevertheless, a team composed of researchers with expertise from one or more of the disciplines involved will serve as a steering committee to provide coordination and continuity among the studies. The project will involve a partnership among academia, government (U.S. and Mexico), industry, and cultural and non-profit organizations.

    Funding for this project will be sought in several phases. Initially, funding will be requested from private organizations and foundations to develop an inventory and database of archaeological materials, to compile relevant literature on extant maize cultivars into a database, and to develop a detailed project plan. Development of appropriate molecular and elemental analysis methodologies will be on-going and may be funded in the form of preproposals for obtaining the preliminary data necessary to demonstrate the feasibility and relevance of these approaches to the overall project. Although the components of the project have their own merit per se, multi-agency funding will be sought from NSF, DOE, and USDA to support a single, integrated research initiative. Funding to establish the student-training labs may be sought separately from other project elements.

    We welcome inquiries, comments, or suggestions on the proposed research initiative. Please direct comments to Dr. Peter Bretting at USDA-ARS North Central Regional Plant Introduction Station, Agronomy Hall G214, Iowa State University, Ames, IA 50011-1010. 

    Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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