Why sexual reproduction? Why four bases?

In nature, the process of sexual reproduction is found to be much more prevalent than the other processes of reproduction. To justify this preference, we present here a model for computer simulation of the process of survival in a colony of organisms, taking into account food and space restriction and invasion by some disease. The algorithm associates with each individual a complementary pair of strings. Each string is a sequence of several “base” units and each base unit can be of four types. We have computed the fluctuation of population for three processes of reproduction and find that the fluctuation is the lowest for sexual reproduction and this might justify the predominance of the same. We have also repeated the simulation for the case when each base unit can be of only two types. The fluctuation of population is now more and the average population is less, which indicates that it is better to have four (rather than two) types of bases.