  A recent survey of the Galaxy and M31 reveals that more than 90% of dwarf
galaxies within 270 kpc of their host galaxy are deficient in HI gas. At such
an extreme radius, the coronal halo gas is an order of magnitude too low to
remove HI gas through ram-pressure stripping for any reasonable orbit
distribution. However, all dwarfs are known to have an ancient stellar
population (\geq 10 Gyr) from early epochs of vigorous star formation which,
through heating of HI, could allow the hot halo to remove this gas. Our model
looks at the evolution of these dwarf galaxies analytically as the host-galaxy
dark matter halo and coronal halo gas builds up over cosmic time. The dwarf
galaxies - treated as spherically symmetric, smooth distributions of dark
matter and gas - experience early star formation, which sufficiently heats the
gas allowing it to be removed easily through tidal stripping by the host
galaxy, or ram-pressure stripping by a tenuous hot halo (n_H = 3x10^{-4}
cm^{-3} at 50 kpc). This model of evolution is able to explain the observed
radial distribution of gas-deficient and gas-rich dwarfs around the Galaxy and
M31 if the dwarfs fell in at high redshifts (z~3-10).
