General Models: Specific Models: Examples in text:

Directed Reciprocation X undertakes a significant cost to benefit Y, and Y in turn reciprocates that benefit back to X. Operates within or between species. (Trivers 1971)	Partner Fidelity Feedback: X and Y are associated for an extended series of exchanges that last long enough that a feedback operates: the effect of benefits transferred from X to Y returns and enhances the fitness of X. Thus, by failing to cooperate, individual X ultimately curtails its own fitness. (Bull and Rice 1991, Nowak and May 1992, Frank 1994, Doebeli and Knowlton 1998, Simms and Taylor 2002 )	-Vertically transmitted symbionts, optimal virulence evolution, ant-acacia mutualism.
	Partner Choice: Either individual X1 or X2 receives a benefit from Y, depending on Y’s choice. Y chooses to interact with the X individual that offers greater fitness returns. (Darwin 1859, Eshel and Cavali-Sforza 1982, Noë 1990, Bull and Rice 1991, Peck 1993, Noë and Hammerstein 1994, Batali and Kitcher 1995, Frank 1995, in press, Wilson and Dugatkin 1997, West et al 2002b)	-Squid-light organ symbiosis, legume-rhizobium symbiosis, yucca-yucca moth symbiosis, image-scoring in reef fish, allogrooming in impala.
Shared Genes X benefits X1 with which X shares alleles through descent from a common ancestor. Operates within species only. (Hamilton 1964a,b)	Kin Choice: X recognizes and directs benefits to more closely related X1 as opposed to more distantly related X2 based on phenotype(s) of X1, X2. (Hamilton 1964a, Eshel and Cavalli-Sforza 1982, Reeve 1989, Queller 2000)	-Exclusion of non-relatives in tunicates, GP9 locus in fire-ants, M-factors in beetles, cell adhesion genes in social amoebae.
	Kin Fidelity: X directs benefits to X1 base upon X1’s context dependent spatial association with X. This proximity denotes shared genes with X. (Hamilton 1964a, Eshel and Cavalli-Sforza 1982, Reeve 1989, West 2002a)	-Parental care in birds, coinfection in clonal microbes, aposemat-ism in familial groups of aphids.
Byproducts X benefits Y as a byproduct of an otherwise selfish act of X. Operates within or between species. (West-Eberhard 1975, Brown 1983)	One Way: An act of X benefits Y as an automatic consequence (byproduct) of X’s self interested action. (West-Eberhard 1975, Brown 1983, Connor 1995a)	-Vultures and lions, carrion feeders.
	Two Way: Both X and Y each benefit the other as automatic consequences (byproducts) of their own selfish actions. Includes synergism: actions or coordinated behavior that are automatically more fitness-enhancing when performed in groups. (Hamilton 1971, Queller 1985, Connor 1995a)	-Predator dilution in bugs, selfish herds, Mullerian mimicry, unrelated helpers at the nest, ant colonies founded my multiple queens.
	Byproducts Reciprocity: Y evolves to enhance its benefit to X, which in turn increases the byproducts it receives from X. The byproduct from X does not evolve, but the effect of Y on X does. (Connor 1986)	-Honeyguide-man mutualism.