Mutualism

J Evol Biol. 2006 Sep;19(5):1365-76.

The evolution of cooperation and altruism--a general framework and a classification of models.

Lehmann L, Keller L.

One of the enduring puzzles in biology and the social sciences is the origin and persistence of intraspecific cooperation and altruism in humans and other species. Hundreds of theoretical models have been proposed and there is much confusion about the relationship between these models. To clarify the situation, we developed a synthetic conceptual framework that delineates the conditions necessary for the evolution of altruism and cooperation. We show that at least one of the four following conditions needs to be fulfilled: direct benefits to the focal individual performing a cooperative act; direct or indirect information allowing a better than random guess about whether a given individual will behave cooperatively in repeated reciprocal interactions; preferential interactions between related individuals; and genetic correlation between genes coding for altruism and phenotypic traits that can be identified. When one or more of these conditions are met, altruism or cooperation can evolve if the cost-to-benefit ratio of altruistic and cooperative acts is greater than a threshold value. The cost-to-benefit ratio can be altered by coercion, punishment and policing which therefore act as mechanisms facilitating the evolution of altruism and cooperation. All the models proposed so far are explicitly or implicitly built on these general principles, allowing us to classify them into four general categories.



J Theor Biol. 2004 Feb 21;226(4):421-8.

Evolution of mutualism through spatial effects.

Yamamura N, Higashi M, Behera N, Yuichiro Wakano J.

Mutualism among species is ubiquitous in natural ecosystems but its evolution is not well understood. We provided a simple lattice model to clarify the importance of spatial structure for the evolution of mutualism. We assumed reproductive rates of two species are modified through interaction between species and examine conditions where mutualists of both species, that give some benefit to the other species with their own cost, invade non-mutualists populations. When dispersal of offspring is unlimited, we verified the evolution of mutualism is impossible under any condition. On the other hand, when the dispersal is limited to neighboring lattice sites, mutualists can invade if the ratio of cost to benefit is low and the intrinsic reproductive rate is low in case where the parameter values are symmetric between species. Under the same conditions, non-mutualists cannot invade mutualist populations, that is, the latter are evolutionarily stable. In case of asymmetric parameters, mutualists tend to invade if the average value of costs to two species is low or that of benefits is high, and if the intrinsic reproductive rate is low for one of the two species. A mechanistic explanation of why mutualists increase when the dispersal is limited is given by showing that mutualist pairs of the two species at the same lattice site rapidly increase at the initial phase of the invasion.


J Theor Biol. 1994 Oct 21;170(4):393-400.

Genetics of mutualism: the evolution of altruism between species.

Frank SA.

Conditions are analyzed under which natural selection favors an individual to help another species at a cost to its own reproduction. Traditional models for the evolution of altruism between species focus on the genetic relatedness between the original donor and the recipients of return benefits from the mutualistic partner species. A more general model is analyzed here that focuses on the synergistic effects between partner species caused by genetic variability. The model shows that the spread of altruism is enhanced by spatial correlations between species in the genetic tendency to give aid to partners. These spatial correlations between species are similar to the kin selection coefficients of relatedness that determine the course of social evolution within species. The model also shows that natural selection and ecological dynamics can create genetic correlations between neighbors of different species, even when the initial spatial distributions of the species are uncorrelated. Genetic correlations between species may play an important role in the origin and maintenance of altruism between species.

Department of Ecology and Evolutionary Biology, University of California, Irvine 92717.