But the lead researcher says modern methods of directly changing the genetic make-up of crops are better.

Professor John Doebley explains how he revealed the ancient farmers' acheivements

The ancient farmers took a wild Mexican grass called teosinte and, by selective breeding, transformed it into maize, the second most grown crop in the world.

However, Professor John Doebley pointed out to BBC News Online: "It took between 300-1000 years of breeding to fix the gene."

Surprising diversity

What surprised the US scientists led by Professor Doebly was that this process did not weed out all but a few varieties of maize. In fact, maize is more genetically diverse than many wild plants.

The trick, discovered by the team at the University of Minnesota and Rutgers University, was that the neolithic farmers breeding programme only fixed one part of the gene controlling the shape of the plant.

The "teosinte branched1" gene determines how many side branches a plant grows. If fewer, shorter, side branches grow then more, larger ears of corn are produced.

The breeding did not alter the part of the gene which determines what protein is produced, but the "regulator" part of the gene which controls how much of the protein is made. By creating plants which made more of the protein, the farmers gained a plant with fewer branches.

Complete transformation

The genetic transformation achieved by the neolithic farmers precisely changed just five regions of DNA to completely change a plant from a wild grass to a productive crop.

Despite this Professor Doebley believes the genetic engineers who today directly change the DNA of crops have advantages.

"Certainly, modern scientists using transgenic approaches can be very precise," he says. "They can manipulate a single base pair. They can take an existing gene and reduce its level of expression. So I think they can be more precise than these ancient peoples."

"The new approaches will accelerate the rate at which improved crops are produced. Within a decade now, one can have a significant change in a crop that would have taken many hundreds of years before."

However, the campaign group, Friends of the Earth (FOE), told BBC News Online that: "Traditional methods have worked for thousands of years and have not caused any harm yet."

"There is a big difference between crossing types of maize to get a stronger variety of maize and taking genes from other species.

"At the moment, scientists do not know what happens when they insert foreign genes into a crop plant. To say it is precise is simply not true," says FOE's Adrian Bebb.