The policing behavior was described as "selfish" because suppression of the cheaters directly benefited the evolved populations themselves rather than being self-sacrificial for the benefit of others. That being said, the selfish police actually do strongly benefit cooperator cells in at least one social context. In mixed groups that include three players -- the evolved cells, the cheater and the ancestral cooperator -- the ancestor produced far more spores than it did when it was mixed with only the cheater.
The evolving populations might have gained the ability to suppress cheaters by a variety of mechanisms, Velicer said.
For example, the descendants of the ancestral cooperator might have evolved a general anti-competitor trait that generically harms a variety of potential competitors to a similar degree, but this did not occur. Rather, the cooperator lineages evolved behaviors that are particularly harmful to the non-evolving cheater. "We would like to investigate the molecular basis of cheater suppression," Velicer said, "in particular whether it is due to the positive production of a compound that is uniquely detrimental to the cheater or some other mechanism."
The scientists competed the strains that evolved to deal with the cheater against their cooperative ancestor, both with the cheater present in the same group and without the cheater. They found that most evolved populations strongly outcompeted their ancestor only when the cheater was present. This result showed that much of the adaptation that took place during the evolution experiment was a specific evolutionary response to the presence of cheater cells.
In an intriguing reversal of fate, some of the replicate populations that evolved from the cooperative ancestor actually became cheaters themselves, but of a new kind. These new cheaters differed from the non-evolving cheater (the one that was
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