GROUP SELECTION. “Two types of interactions have been evidenced: negative interactions (also termed interfering interactions) by which some genomes affect negatively the replication of other genomes of the same ensemble, and positive interactions (akin to classical complementation) by which genomes reinforce each other to achieve a higher replication rate. The result of these interactions is that evolution operates at the level of the population, a process often called ‘group selection”.”
http://www.sciencedirect.com/science/article/pii/S0042682215001580