[Below is the original script. But a few changes may have been made during the recording of this audio podcast.]

Humans have been genetically modifying crops for millenia the old-fashioned way—selective breeding. But new techniques that insert foreign genetic material, say bacterial genes to produce insecticide in a corn plant, have raised health and environmental concerns. And that has prompted European countries, most recently Germany, to ban genetically modified, or GM, crops.

Proponents argue that GM crops can help feed the world. And given ever increasing demands for food, animal feed, fiber and now even biofuels, the world needs all the help it can get.

Unfortunately, it looks like GM corn and soybeans won't help, after all.

A study from the Union of Concerned Scientists shows that genetically engineered crops do not produce larger harvests. Crop yield increases in recent years have almost entirely been due to improved farming or traditional plant breeding, despite more than 3,000 field trials of GM crops.

Of course, farmers have typically planted, say, GM corn, because it can tolerate high doses of weed-killer. And the Biotechnology Industry Organization argues that GM crops can boost yields in developing countries where there are limited resources for pesticides.

But it appears that, to date, traditional plant breeding boosts crop yields better than genetic modification. Those old farmers were on to something.

—David Biello