The calculus of looping sequences is a formalism for describing theevolution of biological systems by means of term rewriting rules. Inthis paper we enrich this calculus with a type discipline whichpreserves some biological properties depending on the minimum andthe maximum number of elements of some type requested by the present elements. The typesystem enforces these properties and typed reductions guarantee thatevolution preserves them. As an example, we model the hemoglobinstructure and the equilibrium between cell death and division: typedreductions prevent undesirable behaviors.
