Modelling the individuals that constitute a population is an extreme form of disaggregation. It is being increasingly recognised as a highly effective approach, for two main reasons. First, it enables the modeller to capture interactions critical to system behaviour that are lost in any more aggregated approach. Second, it frequently is much easier to construct individual-based models, since the behaviour of and interactions between individuals are frequently quite simple, but can lead to complex patterns of behaviour of the whole population (e.g. ant colonies).
If you have a fixed number of individuals, then you can use Simile's fixed-membership submodel. If, as is likely to be the case, the number of individuals in the population changes dynamically, then you would use Simile's population submodel, adding the three symbols needed to specify the initial number of individuals in the population, the way in which new individuals are created, and the way in which individuals are killed off.