Cooperative societies can be very successful, but they also have a vulnerability that can be devastating: They can be destroyed by cheaters who mooch off the labors of others without donating any of their own. If cheaters become too common, the few remaining cooperators can’t carry out all the work the society needs to survive.

Dr. Archetti and his colleagues have found evidence that cancer cells cheat one another, too. They reported their research this week in Proceedings of the National Academy of Sciences.

The cheating they discovered takes place in pancreas tumors. Scientists have long known that some of these cancer cells gain a mutation that causes them to make a growth-stimulating chemical called IGF-II. In many cases, these tumors contain other cells that don’t produce IGF-II. Dr. Archetti and his colleagues wondered if the nonproducers were taking advantage of the producers.

To find out, the researchers mixed together the two types of cells in the lab and observed their growth. The scientists found that nonproducer cells thrived on the IGF-II made by the producer cells, growing faster than they would on their own.

Yet the producer cells got no advantage from being in the mixture, suggesting that the nonproducers really do cheat.

To see how harmful this relationship could be, the scientists reared the mixed cells under different conditions. Sometimes, the cheaters wiped out the IGF-II producers, the scientists found.

One way to let the cheaters win was to rear the cells in a rich broth of nutrients and growth factors. The cheating cells grew quickly. The IGF-II producing cells, by contrast, lagged behind. They were using up energy to make unnecessary growth factors, which they could have used to grow fast. Over time, the cheating cells completely took over the population, the scientists found.