Growing meat without growing animals.

Read Daniel Engber's " Science" column on the fake-meat prize.

Two years ago, I proposed a compromise between carnivores and vegetarians: We couldn't change our craving for meat, but we could change the way we sated it. The solution was to grow meat in labs, the way we grow therapeutic tissue from stem cells.

Looks like I might get my wish.

People for the Ethical Treatment of Animals has just offered a $1 million prize to anyone who develops a commercially viable "in vitro chicken-meat product." The catch is that the product can't contain or entail the use of "animal-derived products, except for starter cells obtained in the initial development stages."

The idea is simple: Instead of growing a chicken embryo into a bird and cutting meat from it, you skip the bird part and grow the meat directly from the embryo.

If you don't believe this can be done, read up on the blood vessels, livers, bladders, and hearts we've already grown in labs. Check out this month's International In Vitro Meat Symposium. Scan the latest updates on "cultured meat" R&D.

It's no freakier or more far-fetched than what you've been hearing from politicians about stem cells and what they can do for people. Scientists aren't even allowed to try a stem-cell experiment in people till it works in animals. That's all PETA is asking for: "animal stem cells that would be placed in a medium to grow and reproduce."

To put it crudely, if you can grow a hunk of flesh for transplant, you can grow it for food.

If this idea repels you as a carnivore, imagine how it feels to a vegetarian. PETA co-founder Ingrid Newkirk tells the New York Times that the prize offer caused "a near civil war in our office" and that "we will have members leave us over this." Newkirk observes, "In any social cause community, there are people who strive for purity."

She's right. I've seen civil wars like this one in other communities. In the case of the abortion-rights movement, I wrote a book about it. Pragmatists thought they could broaden the movement's appeal by changing its language and arguments. Purists worried that these changes would narrow the movement's agenda. Both sides were right. This is an important lesson in politics: Message, constituency, and agenda are related. The broader your message, the broader your constituency, and the narrower your agenda. You have to choose your trade-offs.