The Selfish Gene

by Richard Dawkins

Imagine we have a population in which all the females are coy, and all the males are faithful. It is an ideal monogamous society. In each couple, the male and the female both get the same average pay-off. They get +15 for each child reared; they share the cost of rearing it (−20) equally between the two of them, an average of −10 each. They both pay the −3 point penalty for wasting time in prolonged courtship. The average pay-off for each is therefore + 15 − 10 − 3 = + 2. Now suppose a single fast female enters the population. She does very well. She does not pay the cost of delay, because she does not indulge in prolonged courtship. Since all the males in the population are faithful, she can reckon on finding a good father for her children whomever she mates with. Her average pay-off per child is + 15 − 10 = + 5. She is 3 units better off than her coy rivals. Therefore fast genes will start to spread. If the success of fast females is so great that they come to predominate in the population, things will start to change in the male camp too. So far, faithful males have had a monopoly. But now if a philanderer male arises in the population, he starts to do better than his faithful rivals. In a population where all the females are fast, the pickings for a philanderer male are rich indeed. He gets the +15 points if a child is successfully reared, and he pays neither of the two costs. What this lack of cost mainly means to him is that he is free to go off and mate with new fem...