Landrace-based genetic materials available for plant breeding or biotechnology programs have already been purposely manipulated by traditional cultivators over centuries and even millennia (Ucko and Dimbleby, 1969; Struever, 1971; Altieri and Merrick, 1987). Although archaeological debates continue over precisely where and how nomadic hunters and gatherers finally began the conscious planting of seeds, roots, or tubers and thereby ushered in the "Agricultural Revolution," the outcome of early farmers' efforts cannot be denied (Hobhouse, 1985; McCorriston and Hole, 1991). The historic tendency for preindustrial agricultural communities has been to foster and increase landrace diversity, rather than decrease it (Harlan, 1995). As long as 8 to 12 thousand years ago, "primitive" farmers had already successfully experimented with invading wild "weedy" species in their settlement clearances and domesticated the first crops (Harlan, 1975). Not only did prehistoric cultivators give humanity the major food crops and animals which nourish us today, they simultaneously created their own specialized knowledge systems about the food, fiber, and medicinal values of thousands of plant and animal species (Schery, 1972; Fowler and Mooney, 1990). While modern science has been appreciative of and concerned about the supply of the genetic raw material provided by farmer curators, much less interest has been shown in the local knowledge or management strategies which underpinned in situ landrace development in the first place (Naz-area-Sandoval, 1990).
De Candolle (1885) and later Vavilov (1926; 1949) were the first to observe that the density of interspecific and intraspecific variation of crop species was found in "centers of domestication" which tended to be in the ecologically complex mountainous regions or areas of marked dry-wet seasons in Africa, Asia, and Latin America (Rhoades and Thompson, 1975). Due to a variety of causes, major ancient civilizations — such as the Andean, Mesopotamian, Mesoamerican, Indus, and Chinese — evolved near these centers in close association with diverse plants and animals. In complex ecological settings under conditions of human population expansion, the coevolution of human culture and plant populations led to a level of people-plant interdependency so high that some modern crops — such as maize — cannot even reproduce themselves without purposeful human intervention (Iltis, 1987). The historical and ethnographic records are rich with data on how cultural knowledge intertwines with the biological to the degree they cannot be separated and still maintain dynamic evolutionary-ecological systems (Nazarea, 1998a). This detailed knowledge not only focused on production but also storage, processing, cooking, and utilization qualities needed for the survival and rejuvenation of crops and humans (Nazarea-Sandoval, 1992). As a result, domesticated crops can be understood as culturally created and conceived human artifacts — valued for multiple qualities such as utility, taste, color, shape, and symbolism (Zimmerer, 1991). Indeed, foods or other materials derived from crops or animals are not just calories for the human body but are integral parts of daily social and cultural lives (Brush, 1992).
The original diversification of crops in the centers of domestication was further enhanced after the Age of Discovery when plants were transferred by explorers between the Old and New Worlds (Hobhouse, 1985). In their new homes, migrating plants were further manipulated by curious cultivators and horticulturists who tested the exotic materials, selected those that did well, and then integrated them into their local farming and gardening systems. However, problems in the transplanted plants soon became evident. Since only a small amount of the genetic variability found in the agroecosystems of domestication made it to the new environments, resistance to disease and pests was often lacking and collapse under the onslaught of disease or pests was devastatingly frequent (Rhoades, 1991). The most famous documented case is that of the widespread potato crop failure in mid-19th-century Europe due to late blight (Phytophtera infestans), a fungus likely introduced from the Americas. Most of Europe had come to depend on a few varieties; in Ireland there was total dependence on a single variety. Combined with political exploitation by the British government, the unfortunate timing of the crop failure led to the deaths of millions of Irish (Woodham-Smith, 1962). A few years later, the grape crop on mainland Europe succumbed to a minute, aphidlike insect (Phylloxera vitifoliae) accidentally introduced from wild American grape stock (Vitis labrusca) (Olmo, 1977). These two incidents spurred a tremendous interest on the part of European scientists to understand not only the nature of disease (plant pathology was born of these efforts), but also the relationship among the centers of genetic origin, natural range of variation, and disease resistance. Although neither Mendelian genetics nor the theory of disease was understood by the 1870s, European farmers appreciated that "renewed" seed stock from the regions where the crops originated brought bloom back to their crops. In the case of postfamine potatoes, a single small Andean tuber direct from South America fetched its weight in gold, thereby creating a potato seed craze as intense as the tulip craze in Holland in earlier times (McKay, 1961). Likewise, European and American plant scientists came to appreciate the link between the well-being of their farmers' crops and the genetic diversity in the homelands of the crops themselves.
Although the importance of genetic material from the centers of diversity and domestication remains highly appreciated by geneticists and crop scientists, there is less awareness of the curator role of extant farmers or pastoral communities and their knowledge which makes it possible for this valuable diversity to be maintained in situ and passed on to the global human family. Historically, most governments have seen marginal tribal and peasant communities as practicing a backward, primitive agriculture ripe for "modernization" through information and technology (Rogers, 1969). As industrial developments in Europe, North America, Japan, and the cities of the Third World attracted wage labor from the countryside, planners and agricultural scientists sought ways to provide cheap and abundant food for the growing urban areas. This cheap food policy, which has intensified in the post-World War II era, meant that the potentially productive agroecological zones (flat, fertile, and hydrologically favorable) were to become targets of planned agricultural change to make them more productive through genetic uniformity and mechanization of the agroecosystem for the purpose of achieving higher yields. One outgrowth of this simplification of the agricultural landscape was the renowned "Green Revolution," which combined scientific plant breeding with input packages for favorable environments (Plucknett et al., 1987). The dramatic increases in world food supply witnessed in the 1960s and 1970s are directly traceable to these crop improvement programs which focused on increasing the productivity of plants though breeding for high response to inputs such as fertilizer (Mellor and Paulino, 1986).
The role ascribed by scientists to local cultivators and their communities during the Green Revolution was that of recipients of "technological" packages of improved seeds, fertilizers, and other inputs, as well as infrastructure development. "Transforming traditional agriculture," as Nobel Peace Prize-winner Theodore Schultz (1964) called the effort, was promoted as the motor for global growth and the most efficient exit from agricultural stagnation and famine. Farmers were seen as individual rational decision makers who only needed to be provided the necessary inputs and knowledge by governments and scientists to get the job accomplished. Hence, breeders made selections and crosses from advanced breeding lines derived from landraces. These lines were tested on experiment stations or controlled farm conditions, and, after a dozen or more years, these materials were released to farmers through certified seed programs, extension efforts, and other mechanisms (Duvick, 1983). Rather than breed for local conditions, breeders aimed for broad adaptability of high-yielding fertilizer-responsive varieties in irrigated, fertile zones. Feedback from farmers in on-farm trials rarely provided information on the suitability of selection for specific locations. The seeds were delivered to farmers largely through the patron-client extension model which focused on the individual farm enterprise, not the community or social groupings of farmers (Duvick, 1986).
The "success" of the Green Revolution was double-edged. Signficant increases in food production were achieved in a short time, leading to the alleviation of food shortages and famine in critical areas (Mellor and Paulino, 1986; Plucknett et al., 1987). However, with this success (along with other forces such as urbanization, out-migration, grazing) and as farmers responded to markets, growth, and development programs by adopting a few high yielding varieties, many landraces were abandoned. Concern over genetic erosion by national and international agencies has led to the creation of a global network of ex situ gene banks and living collections where landraces and wild materials are kept in short- and long-term seed storage (Plucknett et al., 1987). Fewer resources, however, have been given to support in situ conservation by native communities, and even less attention has been aimed at preserving the knowledge of local peoples regarding plants, a critical legacy just as vulnerable to erosion (Nazarea, 1998a).
This historical ecological-evolutionary trajectory of traditional in situ management of landraces underscores the following points:
1. The often controversial proposal to maintain the dynamic evolutionary management of landraces within traditional landscapes is based on the historical reality of marginal farmers as folk curators;
2. Despite the tendency of modern agricultural science to separate the genetic "resources" from the local knowledge base, both are essential components of in situ maintenance of diversity and, by extension, a well-supplied ex situ system; and
3. Despite the loss of diversity in the "favored" environments, rich gene pools still exist in many farming communities which survive along the margins of the world economic order. These marginal rural populations are often seen — even by conservationists — as a threat to biodiversity in protected areas and surrounding buffer zones. Our approach is to see them as part of the solution.
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