Brans--Dicke scalar--tensor theory provides a conformally coupling of the
scalar field with gravity in Einstein's frame. This model is equivalent to an
interacting quintessence in which dark matter is coupled to dark energy. This
provides a natural mechanism to alleviate the coincidence problem. We
investigate the dynamics of this model and show that it leads to comparable
dark energy and dark matter densities today.Comment: To appear in Pramana Journal of Physics, 201