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PEOPLE first cultivated maize much earlier than previously thought, say
archaeologists who鈥檝e been studying the oldest cobs unearthed so far from caves
in southern Mexico. The prehistoric specimens suggest that maize鈥檚 wild
ancestors were domesticated at least 6500 years ago. But we may never know where
the first corn grew.

Maize is one of the world鈥檚 most important crops. And researchers think
ancient Central Americans created it by breeding desirable traits into a wild
annual grass called teosinte. The grass produces wheat-sized clusters of grain,
which explains why the oldest cobs found are no bigger than a small pencil.

Ten years ago, scientists used radiocarbon dating to show that cobs from a
cave in the Tehuac谩n valley were 5500 years old, leading some
archaeologists to suggest that maize originated in the region.

Now cobs have been found in caves at Guil谩 Naquitz two hundred
kilometres to the south (see map)
that are even older. Dolores Piperno of the
Smithsonian Tropical Research Institute in Panama and Kent Flannery, curator of
the Museum of Anthropology at the University of Michigan in Ann Arbor, say the
maize was harvested 6250 years ago. But people must have been planting teosinte
even earlier, Piperno says. 鈥淭he cobs are tiny, but they are completely
诲辞尘别蝉迟颈肠补迟别诲.鈥�

Bruce Benz, an archaeologist at Texas Wesleyan University in Fort Worth,
compared the cobs with modern teosinte. He discovered that careful breeding had
produced a plant with densely packed kernels lacking the protective sheaths
found in the wild grass.FIG-mg22781001.JPG

Exactly how long it took ancient Meso-Americans to breed these changes into
teosinte is anyone鈥檚 guess, says Edward Buckler, a geneticist at North Carolina
State University in Raleigh. Modern maize has at least five regions of DNA that
are different from teosinte. Each controls a trait, such as kernel size, and at
least two had already changed by the time of the cave specimens. This would have
taken hundreds of years, says Buckler. 鈥淏ut you could easily imagine it
stretching out for 5000 years or more,鈥� he says.

Genetic data suggests that maize鈥檚 wild ancestor is a subspecies of teosinte
found in the wet lowlands of the Central Balsas Valley, 400 kilometres
north-west of Guil谩 Naquitz. So it may have been domesticated there
first. Buckler agrees. The caves are in an area too dry for teosinte to grow, he
says. But ancient cobs are less likely to be preserved in wetter areas, so we
may never find remnants of the first maize. 鈥淲here you find archaeological
records is not necessarily where things happened first,鈥� he says.