  Brane Gas Cosmology (BGC) is an approach to unifying string theory and
cosmology in which matter is described by a gas of strings and branes in a
dilaton gravity background. The Universe is assumed to start out with all
spatial dimensions compact and small. It has previously been shown that in this
context, in the approximation of neglecting inhomogeneities and anisotropies,
there is a dynamical mechanism which allows only three spatial dimensions to
become large. However, previous studies do not lead to any conclusions
concerning the isotropy or anisotropy of these three large spatial dimensions.
Here, we generalize the equations of BGC to the anisotropic case, and find that
isotropization is a natural consequence of the dynamics.
