Frank, S. A. 1995. Mutual policing and repression of competition in the evolution of cooperative groups. Nature 377:520-522.

One outstanding problem in evolutionary theory is how competition among lower-level units is suppressed in the formation of higher-level evolutionary units. For example, the key problem of early evolution is how small, individual replicators formed cooperative groups of sufficient complexity to allow accurate copying of the genetic material. The puzzle is why parasites did not subvert the formation of cells by obtaining benefits from the group without contributing to shared traits that enhance reproduction. These parasites would outcompete other replicators within the cell, disrupting reproductive fairness among subunits and destroying the functional coherence of the group. A similar problem arose at a later evolutionary stage with the orderly mendelian segregation of subunits (chromosomes) within cells, and reproductive fairness continued to be a problem in the evolution of insect and human societies. Here I present a simple model to show how reproductive fairness evolves among subunits to create functional coherence and higher-level units. Self-restraint, which evolves according to the kin selection coefficient of relatedness, is not sufficient: mutual policing and enforcement of reproductive fairness are required for the evolution of increasing social complexity.