The point behind using a set of problems connected with memorising sequences of numbers is that we don't believe in rewarding organisms in our model who perform in a pleasing manner directly with reproductive success, rather we prefer to pay them for their services, and then charge them for reproductive facilities at a later date. There are essentially two main methods of implementing such a scheme, one involves offering the organisms a precious material, or scarce vitamin, essential to reproduction in payment for their services. The other is to pay organisms for their services in e-money and then extract payments from them when they attempt to reproduce. We have chosen the second alternative over the first on the grounds that it simplifies our model. Paying organisms with e-money allows them more choose concerning when they reproduce, provides a medium of exchange for trade within the model and encourages parasites within the model.
Parasites are important for the evolution of sex.