If there is a high reward or many benefits for the individual that initiated the cooperative behavior, mutualism should be selected for. When researchers investigated the co-evolution of cooperation and choice in a choosy host and its symbiont (an organism that lives in a relationship that benefits all parties involved), their model indicated that although choice and cooperation may be initially selected for, this would often be unstable.[4] In other words, one cooperative partner will choose another cooperative partner if given a choice. However, if this choice is made over and over, variation is removed and this selection can no longer be maintained.