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Cooperation is a key driver in the evolution of multicellular organisms as well as societies. Molecular biologist Gad Shaulsky at Baylor College of Medicine in Houston, Texas, teamed up with evolutionary biologists to find 'cheater' mutations — those that enable some strains to benefit from the cooperation of others — in the social amoeba Dictyostelium discoideum, an organism that alternates between a unicellular and a multicellular form (see page 1107). They found cheater mutations in more than 100 genes. Shaulsky tells Nature that even cooperative species sometimes cheat to survive.

Your early work was on cancer — how did you get into the social dynamics of amoeba?

While working on the tumour-suppressor gene p53 as a student, I became interested in communication between cells. I was curious to know why some cells risk foregoing their own survival to become part of a multicellular structure. To answer this question, I needed a social organism that can form chimaeras — organisms that combine DNA from two or more genetically distinct individuals. In conditions of starvation, multicellular chimaeras of the normally unicellular Dictyostelium form, in which spores (live cells) and stalk cells (dead) arise from genetically equitable mixtures of two or more strains.

How did the work on cheating come about?

In 2000, before we collaborated, two of our co-authors at Rice University discovered that one Dictyostelium strain makes more than its fair share of spores within chimaeras — in other words, it cheats. Rice is only across the street from Baylor, but we didn't team up until later that year, when we were all at a meeting in Scotland. We decided to search for cheater mutations and, to our surprise, found more than 100 genes involved in cheating — which suggests frequent opportunities for cheating in natural populations.

Is this subterfuge unique to amoebae?

No. The large number of genes we discovered indicates a long evolutionary history of social competition.

Can Dictyostelium shed more light on sociality?

Yes. Of the organisms whose genomes have been sequenced, there are no other social eukaryotes that are also amenable to genetic modification. Evolutionary biology is a field with many robust theories, and we want to test them at the molecular level. The molecular details of these mechanisms almost certainly differ between species, but the concepts will probably be the same. We think Dictyostelium will become the E. coli of social evolution for the coming decade.