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The World Health Organization now says the weed-killer glyphosate, better known as Roundup, probably causes cancer. Most corn and soybeans produced in the U.S. are treated with glyphosate.

But, Americans don't eat much corn — not unless you live on Fritos, or maybe Coca-Cola, which is sweetened with corn syrup. We instead eat animals that eat corn: cows, pigs, chickens. Maybe we’re consuming glyphosate when we eat a nice, juicy steak or an Egg McMuffin.

If we ended up switching away from chemicals like the Monsanto-marketed Roundup — say, if all our animal feed were organically grown — how much would our eggs and milk cost? 

To start with: Organic corn costs more. From $11 a bushel to almost $14, according to the U.S. Department of Agriculture, with conventional corn selling for less than $4

But animal feed is a relatively tiny part of the cost of our food. You know how many eggs you get from a bushel of corn? More than 200 eggs, which is less than two cents worth of corn per egg. Triple that cost, by using organic corn to feed the chickens, and you're only at six cents.

Higher feed prices do not tend to push up grocery bills, says Bruce Babcock, an economist at Iowa State University who studies corn.

"We did run this experiment where we doubled the price of corn," he says, and he’s not talking about an experiment in the lab, this was in the real world. The price of corn goes up and down, and you can see what grocery prices do.

"It wasn’t so long ago that we had $8 corn, not $4 corn," he says, "and people hardly noticed at the supermarket."

So, why did I pay almost five bucks for a dozen organic eggs yesterday? I asked David Bruce, who runs the egg program at the Organic Valley co-op. His members sold $50 million worth of eggs last year.

He says, organic producers do have other costs — and the distributor and the store both take a cut of my $5. But basically, he says, I paid that much because I wanted them — and so did a lot of other people.

"Demand is outstripping supply," he says. "You know, we’re filling orders at 60 percent," meaning, if a distributor asks for a 100 cases, a farmer can only send 60.

If the whole world went organic, there would be more supply — more organic corn, more organic chickens — and price would probably come down.

Follow Dan Weissmann at @danweissmann