  We review the emergence of the ten-dimensional fermionic closed string
theories from subspaces of the Hilbert space of the 26-dimensional bosonic
closed string theory compactified on an $E_8\times SO(16)$ lattice. They arise
from a consistent truncation procedure which generates space-time fermions out
of bosons. This procedure is extended to open string sectors. We prove that
truncation of the unique tadpole-free $SO(2^{13})$ bosonic string theory
compactified on the above lattice determines the anomaly free Chan-Paton group
of the Type I theory and the consistent Chan-Paton groups of Type O theories.
It also predicts the tension of space-filling D-branes in these fermionic
theories. The derivation of these fermionic string properties from bosonic
considerations alone points towards a dynamical origin of the truncation
process. Space-time fermions and supersymmetries would then arise from bosonic
degrees of freedom and no fermionic degrees of freedom would be needed in a
fundamental theory of quantum gravity.
