 A more interesting situation arises when the heterozygote is superior in fitness to both of the homozygotes, i.e., \(w_{12} \gt w_{11}\) and \(w_{12} \gt w_{22}\)—a phenomenon known as heteroygote superiority. Intuitively it is clear what should happen in this situation: an equilibrium situation should be reached in which both alleles are present in the population. Equation (2) confirms this intuition. It is easy to see that \(\Delta p = 0\) if either allele has gone to fixation (i.e., if \(p = 0\) or \(q = 0)\), or, thirdly, if the following condition obtains: