Corn's Slow Path to Stardom: Archeologists Rewrite the History of Maize - and New World Civilization
Raloff, Janet, Science News
From humble origins as a lowland tropical grass, corn developed into the western world's preeminent grain. Wherever this "gift of the gods" was introduced, it edged out native crops to become an indispensable part of the diet. Because its unparalleled yields allowed communities to grow far beyond what hunter-gatherers or nascent agriculture could feed, most archaeologists viewed corn as having largely fueled pre-Columbian growth --and civilization- throughout the Americas.
But new findings are drastically altering researchers' notions about the time frame over which that revolution occurred. Moreover, new dates for corns emergence from Mesoamerica do not support the widely held view that corn -- or maize, as this grain is called outside the United States - suddenly exploded into stardom wherever it appeared. Indeed, the dogma that this cereal fostered the settlement of nomads by launching agriculture is going the way of myth. Archaeological evidence now suggests that most of the ancients who first embraced maize were already horticulturists -- even farmers.
Corn, while unique in the strength of its impact and the complexity of its domestication, no longer appears unique in the speed at which it moved from botanical curiosity to dietary staple.
When Columbus reached the New World, corn was the most widely grown plant in the Americas, observes Frances B. King, a paleoethnobotanist at the University of Pittsburgh. The grains range extended from what is now southern Canada to lower South America. Some tribes cultivated it at sea level, others at elevations exceeding 11,000 feet.
"Columbus had no way of knowing that maize was far more valuable than the spices and gold he had hoped to find, or that it represented - as it still does today -- the most remarkable plant-breeding accomplishment of all time," King maintains.
Through human intervention, this versatile plant has developed into several hundred races, orvarieties. Their heights vary from 2 to 12 feet, and their maturity ranges from little more than 2 months to almost a year. Their ears vary not only in color - from blue and maroon to yellow and white - but also in size, from 1 to 18 inches. Some maizes thrive in areas receiving more than 170 inches of rain per year, others where annual precipitation averages just 5 inches.
Unlike other cereals, maize bears little resemblance to its wild ancestors. In fact, it deviates from the appearance of its immediate ancestors more than any other cultivated plant known, says Dolores R. Piperno of the Smithsonian Tropical Research Institute in Balboa, Panama.
By backcrossing a number of corn varieties in the 1930s, cereal breeder Paul C. Mangelsdorf of Harvard University attempted to "arrive at some sort of model of what that [progenitor] maize was supposed to look like," says archaeologist Nikolaas J. van der Merwe, also of Harvard. The suspected parent -- some extinct, pod-bearing popcorn - wrapped each seed in a chaff-like glume, the same type of wrapper that encases individual wheat seeds, Van der Merwe says.
Though this theory of corns ancestry won some following among archaeologists for several decades, "I don't think Mangelsdorf was ever very widely believed among geneticists," says John Doebley, a plant biologist at the University of Minnesota in St. Paul. And in the early 1970s, even archaeologists abandoned Mangelsdorf's hypothesis in favor of one initially proposed in 1939 by Nobel laureate geneticist George Beadle.
The shift occurred because several new lines of genetic evidence emerged to point, as Beadle had, to teosinte - a decidedly non-extinct Mexican grass - as corns most likely ancestor, Doebley says.
In fact, paternity and maternity tests conducted in the late 1980s by Doebley and his co-workers show that just a few genes control most of the traits distinguishing corn from teosinte (pronounced tay-o-SIN-tay). "I would say that five is a good number," Doebley says. …