When a polycrystalline fiber is heated for some time, grains change shape and may evolve to one of two equilibrium configurations: isolated spheres, or truncated spheres that remain connected. To which configuration do the grains evolve? How long does this evolution take? These are global questions, and call for a global way to look at the phenomenon. The fiber is a nonequilibrium structure. The free energy consists of the surface and grain-boundary energies; it is the reduction of this energy that drives the diffusive flux of atoms on the surfaces and the grain boundaries. We describe the grain shape using two generalized coordinates, the grain length and the dihedral angle. The free energy is expressed as a function of these coordinates. In the space of the free energy and the coordinates, the energy function is represented by a surface, or a landscape. A point on the landscape represents a nonequilibrium state in general, and the bottom of a valley represents an equilibrium state. We use a variational principle to assign a viscosity matrix to every point on the landscape. The approach leads to a set of ordinary differential equations that govern the evolution of the generalized coordinates.