In the slime mold example, a mutation in a cell adhesion gene caused the mutants to behave selfishly in a lab setting and usually end up producing spores in capsules. Why is the cell adhesion gene considered an example of a "green beard" gene?
In nature, the "selfish" allele is the most successful.
In nature, the "selfish" allele is excluded from joining the aggregation.
In nature, the mutant is no longer selfish.