Historians still squabble over whether there really was a "first" American Thanksgiving. But a handful of documents give us a hint at what might have been served: likely roasted venison and fowl—probably turkey and a number of other wild birds—dried Indian corn, wheat, barley, and fish. The local diet also included lobster, eel, nuts, squash, beans, and berries.

Today's Thanksgiving feast similarly celebrates the bounty of nature, though many of the varieties of corn, squash, and other fruits and vegetables Native Americans and European settlers farmed no longer exist.

Four centuries later, we have come to depend increasingly on only a handful of commercial plant varieties for our food supply. And we see signs everywhere of what some observers call the sinking ark of agricultural biodiversity (agrobiodiversity).

As we sit at the table to give thanks, most of us eat the same commercial variety of turkey—the Broad-breasted White (BBW)—fed with genetically modified corn and soy meal in giant turkey mills. Our stuffing is made from a handful of wheat, corn, and soy varieties cultivated with tractors and fertilizers and bred to resist pests, plagues, and drought. And when you pass the potatoes, you're probably passing one of the three kinds that, since the 1970s, have made up three-quarters of the U.S. potato crop.

In the United States, of 7,000 apple varieties that were grown by the 1800s, fewer than a hundred are cultivated today. More than nine out of ten of the varieties in the official U.S. Department of Agriculture seed list of 1903 were no longer available by the 1980s.

This genetic erosion is common throughout the planet as a result of changing agricultural practices. Wherever we look, we see the rise in uniformity of agricultural plant varieties and a loss of genetic diversity, with many traditional varieties and wild relatives of today's crops simply disappearing.

Over the millennia that humans have engaged with agriculture, about 7,000 plant species have been cultivated or collected for food. But today, according to the United Nations' Food and Agriculture Organization (FAO), fewer than 150 species are under commercial cultivation and only 30 species provide 95 percent of human food energy needs. In fact, just four of them—rice, wheat, maize and potatoes—provide more than 60 percent of human dietary energy supply.

The narrowing of crop diversity has accelerated to frightening proportions in recent decades as a result of three processes: the introduction of commercial, scientifically hybridized plant varieties (mainly since the mid-twentieth century); the expanded use of certain high-yielding varieties as part of the Green Revolution in agricultural production of the 1960s and 1970s; and the expansion of industrial agriculture.

Growing genetic uniformity poses a variety of possible threats to the human food supply. As awareness of the problem has grown over the past three decades, governments, international organizations, and businesses across the world have begun to store available genetic material in gene banks—vaults where scientists conserve seeds away from their original habitats in specially designed buildings at temperatures below freezing.

But are these seed arks enough to stave off a potential food catastrophe? And what other ways are there to ensure human food security? In the long term, keeping farmers on the farm cultivating a wide diversity of locally adapted crops may be the best solution.

The Perils of Declining Food Crop Diversity

A number of risks accompany the loss of genetic diversity in agriculture, including crop disease, pests, climate change, and the rising human population.

Cultivating large areas with one or two high-yielding crop varieties can be disastrous when that crop falls victim to disease. To take one recent example: In Brazil, the world's largest producer and exporter of oranges and orange juice, the genetic uniformity of the country's sweet orange trees has left the citrus industry susceptible (since 1987) to a bacterial disease that causes economic losses that were as high as $250 million U.S. dollars in 2000.

The most famous case of the disastrous outcomes of monoculture is probably the Irish potato famine. European colonizers introduced the potato to European cuisine, and it became the main staple crop in the cold, rainy climate of Ireland. Irish farmers planted primarily one potato variety, the Lumper potato, which was exposed to a deadly fungus in 1845.

Because of genetic uniformity, the fungus contaminated and wiped out much of the potato crop. In the following decade, the famine killed approximately one million people and resulted in the emigration of another million from Ireland.

These days, a major new risk is at the door. A virulent cereal stem rust (Ug99) now attacks previously resistant genes worldwide. The fast mutating fungus, first identified in Uganda in 1999, has now spread across Sub-Saharan Africa, North Africa, and the Middle East. Scientists predict that Ug99 will infect other areas, including North America, in less than ten years.

Because of the spread of monocultures and the narrowing of wheat's genetic basis, almost 90 percent of the world's wheat is defenseless against Ug99. Not only local farmers but also commercial breeders and scientists have to find and develop adaptive traits, which is only possible when we have agrobiodiversity.

Agrobiodiversity conserves multiple food species, ensures genetic variability within species, and preserves diverse farming techniques and knowledge. It allows farmers to switch quickly from one crop variety to another when a certain strain no longer produces good results in the local environment.

In the Peruvian Andes (in contrast to Ireland), where potatoes were first domesticated about 13,000 years ago, Incas cultivated several potato varieties as insurance against crop failures. Today, Andean farmers still cultivate multiple potato types in different shapes, colors, and flavors for reasons of culture, diet, and food security.

Heterogeneous genetic characteristics provide several benefits such as agronomic qualities like resistance to pests, diseases and drought, and adaptations to abiotic stresses such as salinity tolerance.

A Turkish wheat landrace collected in 1948 was found to carry genes for resistance and tolerance to various disease causing fungi. Plant breeders in the United States have used these genes to breed wheat varieties that are resistant to a range of diseases. These genes became a parent of many of the wheat cultivars now grown in the northwestern United States.

A dwarf wheat landrace from Japan was introduced to the United States in 1946. It was used as a donor of dwarfing genes, which increased production by improving nitrogen uptake. Similarly, Zerazera sorghums from Ethiopia have provided resistance to downy mildew for many inbred lines in the U.S. and Mexico.

Agrobiodiversity also provides a foundation for food security, livelihoods, and insurance by sustaining agriculture in the face of global environmental threats such as climate change. Climate change could, for example, make it impossible to grow a certain crop over a large area where it is now cultivated. Meanwhile other plant varieties that might have flourished under the changed conditions have been lost to monoculture itself. The absence of crop diversity certainly renders humanity less adaptable to changes in climate.

Of course, the rapidly growing human population makes food security an ever more acute problem. With the world's population recently passing seven billion—and with a larger portion of those humans now demanding a diet rich in meat—a restriction in the global food supply would mean a human catastrophe. [Read Origins for more on food systems and rising population.]

Rising Malthusian fears that agriculture cannot keep up with a rapidly expanding population have worsened with the threat of climate change and new diseases. Policymakers have been slow to address the threats posed by the genetic erosion of agriculture, often demanding more evidence and questioning its implications for food security.

The issue before us is how to use, conserve, and sustain agrobiodiversity, while we depend increasingly on a limited number of commercial varieties for our food supply.

A Brief History of Seeds and Hybrids

First as gatherers, then as farmers, humans have long relied on plants for food security and self-sufficiency.

Agriculture represents a critical interaction of people and nature. For millennia, farmers have carefully selected and bred new crop varieties from semi-wild relatives of crops in order to optimize their yields in local conditions.

Food security in many parts of the world still depends on the availability of such locally adapted crops. Farmers in isolated areas of Turkey, for example, still cultivate the semi-wild relatives of wheat cultivated 8,000 years ago. Corn (maize) biodiversity in Mexico still endures despite pressures on farmers for modernization.

At the same time, humans have long moved genetic resources (in the form of seeds) from one place to another through migration and trade.

Agricultural crop seeds were exchanged on the Silk Road. In the so-called Columbian Exchange that followed in the wake of Columbus's "discovery" of the Americas, European colonizers transformed agriculture both in the colonies and in Europe by bringing seeds, animals, germs, and other goods from one continent to the other.

Yet, for all humanity's long history with agriculture, the twentieth century witnessed the rapid creation of hybrid seed varieties and modified crops, which quickly spread across the globe. Seed manipulators are no longer farmers experimenting with different strains and species on their farms, but scientists employed by agribusiness to produce new genetic varieties in their laboratories.

With the development of Mendelian genetics in the nineteenth century and the rise of a seed industry as part of modern agriculture, seed breeding has become both a scientific and commercial activity.

In the United States, hybrid corn (maize) was produced as early as 1909. By the mid-1920s, public agricultural research institutions and land-grant colleges were training farmers to produce their own hybrid seeds. The development of hybrids enabled an increase in farm output, but also allowed breeders to assert control over the seed supply.

The U.S. Plant Patent Act of 1930 enabled patents of new plant varieties, increasing the commercial impetus for companies to gain control over seeds and to tackle pressing agricultural dilemmas.

For example, one of the oldest adversaries of wheat and barley is stem rust, caused by a fungus that affected crop cultivations for centuries. It contributed to major crop losses in the United States in the 1930s and 1950s.

In the 1950s, a number of stem rust-resistant genes were described, cataloged, and collected from several wheat varieties from Europe and the Middle East to create new resistant wheat varieties in the United States. These were then cultivated widely, from Africa to Europe, and from China to the United States. The incidence of stem rust was reduced almost to insignificance by the mid-1990s.

Between 1940 and the 1950s, as seed companies stepped into the crop hybridization process—and produced new, high-yield, resistant varieties—their profits tripled.

Technology transformed agricultural research and development. Seeds became not an outcome of farmers' ingenuity but a private commodity. New varieties of seeds could no longer be saved or traded, but had to be purchased by farmers.

Protection of the scientific knowledge of modern seed production promoted further innovation in seed science, but mainly protected the rights of private companies—sidestepping farmers in the seed development process.

Thus, "progress" in agriculture has often been premised on a distinction between "modern" crop varieties, including high-yielding, certified, and now genetically engineered crops, and farmer-saved or semi-wild relatives of crops also known as traditional varieties.

These modern crop varieties reflect the mentality of recent agriculture that lionizes a technological-fix approach. It relies on a simple assumption: If we increase food supply through increased yields, we will address hunger and food security.

This narrow focus on "progress" through modern varieties has facilitated the further loss of diversity on the farm and at the dinner table.

The Green Revolution

With the belief that these new, modern, commercially protected varieties and techniques were the way of the future, it only made sense for the businesses that produced them that they should export their products to the rest of the world.