  We study Dirac spinors in Bianchi type-I cosmological models, within the
framework of torsional $f(R)$-gravity. We find four types of results: the
resulting dynamic behavior of the universe depends on the particular choice of
function $f(R)$; some $f(R)$ models do not isotropize and have no Einstein
limit, so that they have no physical significance, whereas for other $f(R)$
models isotropization and Einsteinization occur, and so they are physically
acceptable, suggesting that phenomenological arguments may select $f(R)$ models
that are physically meaningful; the singularity problem can be avoided, due to
the presence of torsion; the general conservation laws holding for
$f(R)$-gravity with torsion ensure the preservation of the Hamiltonian
constraint, so proving that the initial value problem is well-formulated for
these models.
