The description above provides two alternative schemes for deciding a probability distribution that defines the likelihood of each individual in the population being selected for reproduction. In an ideal world, the mating pool of parents taking part in recombination would have exactly the same proportions as this selection probability distribution. This would mean that the number of any given individual would be given by its selection probability, multiplied by the size of the mating pool. However, in practice this is not possible because of the finite size of the population, i.e., when we do this multiplication, we find typically that some individuals have an expected number of copies which is noninteger – whereas of course in practice we need to select complete individuals. In other words, the mating pool of parents is sampled from the selection probability distribution, but will not in general accurately reflect it, as was seen in the example in Sect. 3.3.