  where \(W_{iA}\) is type \(i\)’s fitness in situation \(A\). This sort of calculation assumes that the effects of the various situations are additive. More complex situations can be modeled, of course, but additive matrices are the standard. It should be noted, however, that matrix-driven evolution can exhibit quite complex behavior. For instance, chaotic behavior is possible with as few as four strategies (Skyrms 1992).