Evolution of Multiple Sexual Preferences by Fisher's Runaway Process of Sexual Selection

The evolution of multiple female preferences by Fisher’s runaway process is investigated. The main factor determining the evolutionary equilibrium is the joint cost of female choice. Multiple preferences evolve when the joint cost of two preferences is little more than the maximum of either cost alone. However, as the joint choice cost increases, one preference tends to dominate. Other preferences persist but are much weaker. The dominant preference is the one which gives the female the greatest Fisherian benefit (more attractive male offspring) relative to the cost of choice. The genetic mechanism controlling preference and the male trait are not crucial in determining equilibrium. Only when the joint cost becomes extreme will all but one preference be lost. Fisher’s process readily explains the presence of multiple sexual ornaments.