Archaeologists writing agriculture's history are gaining new insight from ancient food remains. They are tracing the progress of crop domestication through genetic changes recorded in DNA samples. This new perspective has already punctured the notion that agriculture was slow off the mark in the Americas. As recently reported research in northern Peru illustrates, agriculture's roots run back some 10,000 years in the Americas, just as they do in the Middle East.
Meanwhile, studies of DNA from ancient and modern cultivated wheats and their wild relatives trace the domestication of this wonder plant over thousands of years. They reveal how wheat's genetic nimbleness allowed breeders to adapt it to a variety of environments to the point where it now supplies 20 percent of humanity's food calories.
The impression that the Americas were agricultural laggards was an illusion created by insufficient data. A review of research into agriculture's origins published in Science last month quotes paleobotanist Tom Dillehay of Vanderbilt University in Nashville, Tenn., who points out that archaeologists "were misled by what was not preserved and what we could not see." Now they are finding fossil remains of ancient crops under old grindstones, hut and hearth floors, and in other once-inhabited places. Dr. Dillehay and colleagues described a wealth of such discoveries in the June 29 issue of Science, which also carried the overall research review.
The researchers conclude that their findings in Peru "provide evidence for early use of peanut and squash in the human diet and of cotton for industrial purposes and indicate that horticultural economies in parts of the Andes took root about 10,000 years ago." The researchers add that the evidence of trade and social complexity they are finding show that this also developed "in the Americas nearly as early as it did in the Old World."
Botanists distinguish between cultivating wild plants and domesticating them. You can cultivate wildflowers in your garden. But they won't be domesticated until breeders change their physical characteristics. Ancient farmers cultivated wild wheat.
Then they began selecting plants for characteristics they valued. Stronger stalks made harvesting easier. An ability to hold on to seeds so the wind did not disperse them made for higher yields.
Jorge Dubcovsky and Jan Dvorak at the University of California in Davis reviewed this long domestication of wheat as it is reflected in the DNA of wheat samples from various ages. They pointed out earlier this month in Science that one central fact stands out: Wheat has what these botanists call a "dynamic genome" that makes it ideal for domestication.
It's all too easy to breed the original genetic diversity out of a wild plant to the point where it's hard for breeders to adapt their favorite crop variety to a changing environment. A new insect pest or a shift from a wet to a dry climate can make a particular variety useless. The DNA record shows that wheat has overcome such so-called genetic bottlenecks by easily reincorporating some of the genetic diversity of its wild ancestors by interbreeding. It also can quickly rewrite its own genome.
The story of humanity's shift from hunter/gatherer to farmer is a tapestry of interwoven threads representing environmental, social, and botanical changes. Scientists are beginning to trace the botanical thread in unprecedented detail.