I will discuss how precise star formation histories, including details on the earliest star formation events, and the pulsational properties of RR Lyrae stars can provide important insight into the origin of the dwarf galaxy types and on the nature of the building blocks of large spiral galaxies. First, based on precise SFHs of Local Group dwarf galaxies, I will show that they can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event, and slow dwarfs that formed a small fraction of their stars at an early epoch and have continued forming stars until the present time (or almost). These two evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal vs dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower density environments than fast dwarfs. Following this result, we propose that the nature of a fast or slow dwarf galaxy is imprinted early on as a consequence of conditions impacting their mass assembly history. At a later stage, interaction with a large host galaxy may play a role in the final removal of the gas. (Gallart et al. 2015, ApJ 811, L18) Second, I will discuss the role that dwarf galaxies may have played in the formation of the Milky Way and M31 halos using RR Lyrae stars as tracers of their ancient stellar component. (Fiorentino et al. 2015, ApJ 798, L12; Monelli et al, 2015, in prep)