evolutionary
Group selection A proposed alternative to inclusive fitness sometimes known as kin selection is the concept of group selection. In this type of evolutionary scenario, small groups of organisms of the same species are effectively acting as single perhaps colonial organisms. It is the reproductive success of the group rather than individuals within the group , compared to other groups of the organism that is the basis of selection. Groups that display cooperative and altruistic traits have a selective advantage over groups that do not. Again, the mathematical analysis is similar and it has been claimed that mathematically group and kin selection are equivalent .169 The costs of a trait must be offset by the benefits, but now the key factor is membership in a particular group and typically, members of a group tend to be related to one another . The life cycle of the bacterium Myxococcus xanthus provides an example of this type of behavior. When environmental conditions are harsh, the cells aggregate into dense, 100 m diameter, fruiting bodies, each containing ~100,000 stress resistant spores. When the environment improves, and prey becomes available, the spores are released en mass and return to active life. They move and feed in a cooperative manner through the release of digestive enzymes, which because they are acting in a quorum mode, can reach high levels.170 A well-coordinated group is expected to have a significant reproductive advantage over more anarchic collection of individuals.