Archeologists Date Farming in N. America to 2000 BC : Prehistory: Evidence suggests the early aboriginal peoples of eastern North America were more advanced than believed, and that the area was one where agriculture developed independently.

Archeologists have found evidence that the prehistoric Indians of eastern North America began growing several kinds of wild plants for food as long as 4,000 years ago, and they were farming their own native crops for hundreds of years before maize, or corn, was first brought here from Central America.

The new evidence establishes the region as one of the half-dozen areas of the world where agriculture is now thought to have originated independently. The findings, which rely on technological advances that can measure the age of single seeds and can detect subtle changes in plants produced by domestication, challenge a longstanding belief that early North Americans learned farming techniques from their more technologically advanced southern neighbors, who are known to have domesticated corn and squash.

“It appears now that eastern North America was largely independent from any substantial cultural influence from Mexico or other parts of Central America,” said Bruce D. Smith, an archeologist at the Smithsonian’s National Museum of Natural History who described the new findings in a recent issue of the journal Science.

The plants that these early farmers domesticated include sunflower; lamb’s-quarter or goosefoot, a common farm and garden weed; sumpweed or marsh elder, a cousin of the sunflower that grows in boggy ground; and Cucurbita pepo, a hard, baseball-sized gourd, that was the ancestor of today’s acorn squash. All were grown for their edible seeds, although Smith said the gourds were also used as containers.

By about 250 BC, the archeological evidence suggests the repertoire of seed crops had expanded to include “little barley,” maygrass and erect knotweed, a plant that Smith said survives today only on an island in Lake Erie.

The transition from simply gathering wild seeds to saving and planting them, and from there to growing substantial quantities for food spanned several thousand years. Smith said the plants themselves probably helped things along because all were opportunists likely to spring up unaided in the disturbed ground around early settlements.

“Initially, it doesn’t appear to have been a very deliberate or high-energy input by humans at all,” he said. “You could almost ask, ‘Who’s running the show, the plants or the people?’ ”

When a patch of sunflowers or wild gourds cropped up near a settlement, the initial response of the inhabitants was probably to pick the seeds and perhaps to keep the patch weeded, Smith suggested. “From there, it’s a relatively small step, but a very important one, for people to save some of the seeds they harvested over the winter and to try to expand the stands of plants that were already growing there,” he said.

For sunflowers, gourds, marsh elder and lamb’s-quarter, Smith and other researchers have been able to determine roughly when eastern woodland Indians took the critical step of sowing seeds and, in effect, domesticating the wild varieties.

They can tell because when a plant is cultivated, certain environmental factors promote changes in its seeds’ size and structure. Seeds that germinate quickly and produce tall seedlings tend to do best. They beat out slower-growing plants and are the ones that farmers harvest to eat and to plant again.

This selection process--a human-powered version of natural selection--favors certain traits in the plants. Selection makes a plant evolve larger seeds with thinner coats, characteristics that are not advantageous for wild varieties. When these traits are found, they are taken as signs of domestication.

Archeologists’ ability to find, date and examine prehistoric seeds has been dramatically enhanced in recent years by new technologies, some quite simple. One technique is water flotation, in which dirt from ancient settlements is dumped into a barrel of water and plant material floats to the top where it is skimmed off. The method has allowed archeologists to recover seeds much more efficiently than the old method of sifting the dirt.

More sophisticated is a technique called accelerator mass spectrometry, which allows researchers to use much smaller amounts of material than were formerly needed to obtain radiocarbon dates for seeds, bones and other organic objects from ancient settlements. By measuring the amount of a radioactive form of carbon, which is present in all living things, they can estimate the age of a seed weighing one-thousandth of a gram with a margin of error of about 100 years either way.

By measuring seeds and looking for such changes with a scanning electron microscope, Smith and other researchers have found evidence that inhabitants of settlements in west-central Illinois, Kentucky and east Tennessee were growing sumpweed, gourds, sunflowers and lamb’s-quarter by about 2000 to 1500 BC.

It took more than a thousand years for inhabitants of eastern North America to move from small-scale gardening to raising crops to store for later consumption. Based on evidence such as the finding of large amounts of edible seed at settlement sites, as well as storage vessels and primitive farm implements, Smith dated the appearance of such early food-producing economies to between 250 BC and AD 200. In settlements of that period, he said, “all of a sudden in different areas of the east you start to find a lot of these seeds.”

Smith said cooking seems to have made an advance at around the same time, with the development of ceramic vessels that people could use to boil seeds and make gruel or stew. Earlier cooks had to be content with simply parching seeds in a fire to break the tough outer coating so they could be chewed and digested.

Learning to grow seed crops probably helped aboriginal North Americans get through the winter, but it did not turn them from hunter-gatherers to farmers overnight, Smith said. Centuries after farming arose, they were still using seed crops mainly to supplement a diet that depended chiefly on wild animals, waterfowl, fish, and nuts, seeds or berries from wild plants.

Maize, once thought to be the plant that brought farming to North America, actually was a latecomer. It arrived in the area around AD 200, but for unknown reasons, it did not become a staple crop until about six centuries later, he said.

One traditional explanation is that the woodlands of central and eastern North America provided such abundance and variety for so long that the drudgery and dietary monotony of farming could be resisted longer than elsewhere.